Should Endurance Athletes Go Keto? Ketosis and Ketogenic Diets for Endurance Athletes in 2020
When it comes to weight loss and endurance performance, dietary ketosis is a strategy everyone asks about. On the surface, ketosis or a ketogenic diet offers everything an endurance athlete could dream of: endless energy, freedom from bonking, and an efficient pathway to weight loss. The diet has been all over mainstream magazines, it’s the subject of several books, and the supplement companies have jumped in with new products and a ton of marketing dollars. So, is it time for cyclists, triathletes, and runners to go Keto?
First, a refresher course on what a ketogenic diet is. To achieve dietary or nutritional ketosis you need to severely restrict carbohydrate intake (fewer than 50 grams of CHO/day) so the body transitions to using ketones for fueling muscles and the brain. Ketones are produced from fat, which is why nutritional ketosis is so appealing to sedentary people as a weight loss solution. It’s appealing to athletes because we have a virtually unlimited reserve of fat calories to pull from but can only store 1600-2000 calories worth of carbohydrate in muscles, blood, and the liver. An athlete fueled by ketones would be theoretically “bonk-proof”, since bonking is the result of running low on blood glucose.
Dietary ketosis for athletes is a hotly contested subject. Proponents point to the metabolic advantage of relying on fat instead of carbohydrate, and critics point out the physiological limitations of eliminating carbohydrate as a fuel for performance. You’ll find bias in both groups, either because scientists and coaches (including me) have been in the high-carbohydrate camp for many years, or because there’s a lot of money to be made by creating a market for new media and supplements around a new high-fat dietary strategy. I recognize my historical bias toward carbohydrate, but have tried to look at the science objectively. Here’s the short conclusion I’ve come to:
Both dietary ketosis and the use of exogenous ketone supplements have limitations that make them difficult to recommend to most athletes. Athletes are better served by periodizing carbohydrate availability in order to maximize training quality and performance outcomes.
And here’s how I arrived at that statement:
Ketosis doesn’t IMPROVE endurance performance
If you do everything right, you may be able to achieve similar performance levels during steady state endurance exercise following a high-carb (50-65%CHO) diet or a low-carb, high-fat (LCHF) diet (70-80% Fat, <5% CHO). This means you may be able to sustain a submaximal pace equally well using either strategy. The LCHF strategy has been shown to increase the utilization of fat for energy, especially in long-term (20 months) fat-adapted athletes (Volek, 2015). However, the oxygen cost for exercise increases while exercising on a LCHF strategy (Burke, 2016 and 2020). It takes approximately 8% more oxygen to liberate energy from fat compared to carbohydrate, which means relying primarily on fat reduces economy.
To win races you have to do two things. You have to be able to go fast in training to induce the stress necessary to stimulate positive adaptation, and second, you have to be able to go fast at crucial times during competition. However, Burke’s findings in 2016 showed that despite nearly doubling the oxidation of fat for fuel during competition, a LCHF dietary strategy made elite racewalkers slower compared to racers using a high-carbohydrate strategy.
Updated Findings from Burke 2020
Twenty-six world-class racewalkers attended a 3.5-week training camp, during which a High Carb (HCHO) group consumed 60-65% carbohydrate and the Low Carb (LCHF) consume 75-80% fat and fewer than 50 grams of carbohydrate per day. Diets were energy matched and all athletes performed the same workouts. Athletes completed a 10k performance test at the beginning and end of the training camp, and the HCHO group improved their 10k performance by 4.8% (2:14 faster) while the LCHF group slowed by 1.6% (1:26 slower). The HCHO group increased their relative economy, meaning they could maintain a given pace at a lower percentage of their maximal aerobic capacity (VO2 max).
Read full text of the study here. Amby Burfoot also wrote a very good piece on the study that’s available on podiumrunner.com.
Some critics of Burke’s 2016 study claimed that the benefits of adapting to a LCFH diet would allow an athlete to improve performance by returning to a diet with high carbohydrate availability during final preparation for competition, the idea being that the combination of high carbohydrate availability and improved fat oxidation would enhance performance. So, for the 2020 study, following the training camp all subjects consumed a high-carbohydrate diet during a two-week taper leading into a 20km racewalk competition.
Some athletes from both groups achieved personal bests in the 20km competition, indicating the training camp and taper were effective. For the HCHO group, performance level in the 20k was improved from the start-of-camp test and similar to their end-of-camp 10k level. The LCFH group, who trained for 3.5 weeks using a low-carb diet and then tapered and raced with high carbohydrate availability, bounced back from their poor end-of-camp 10k results to achieve a performance gain over their start-of-camp test that was similar to that of the HCHO group. In other words, the training worked and the performance detriment from the LCHF diet disappeared after the reintroduction of carbohydrate, but no additional performance benefit was gained.
One of the primary goals of endurance training is to increase the pace or power an athlete can sustain at any given percentage of his or her maximum aerobic capacity (VO2 max). Dietary ketosis or a LCFH dietary strategy makes an athlete utilize more oxygen to go the same pace, meaning that during steady state exercise you are operating at a higher percentage of your VO2 max for no performance improvement. When it comes time for high-intensity efforts that are necessary to win races (even for ultra-endurance cyclists, iron-distance triathletes, and ultramarathon runners), this reduction in economy lowers your maximum power/pace at VO2 max. Diet ketosis and LCHF will increase fat oxidation during exercise, but the ability to improve fitness and competitive outcomes depends on more than your ability to burn fat.
Ketosis is physiologically limiting
Without stored and exogenous carbohydrate during competition, you have very little fuel available for anaerobic glycolysis, the metabolic shortcut that rapidly produces energy by partially burning carbohydrate to meet elevated energy demands during short, high-intensity efforts. Ketones can be converted to acetyl-coA and metabolized aerobically in mitochondria, but you miss out on the turbocharged boost from anaerobic glycolysis. You also miss out on the lactate produced from anaerobic glycolysis, but lactate isn’t the enemy it was once thought to be. It is partially-burned carbohydrate that gets broken down to usable energy.
The reason I say you’ll have little carbohydrate available for anaerobic glycolysis instead of no carbohydrate is because an athlete in ketosis can still produce glucose in the liver via gluconeogenesis. In plain English this means athletes in ketosis have limited capacity for high-intensity efforts that rely on carbohydrate for fuel. (It is intriguing to note the amount of available glycogen increased in the long-term fat-adapted athletes in Volek’s study with elite ultrarunners.)
Adapting to a HCLF diet also has the effect of impairing glycolytic pathways by downregulating enzymes necessary for burning carbohydrate during high intensity efforts. As a result, the thought is that the oxidation of carbohydrate is limited even when there is plenty of carbohydrate available.
Almost all endurance sport are actually intermittent-intensity sports rather than steady state intensity activities. While long cycling event may have a moderate overall intensity, there are periods of high-intensity within it. Even ultramarathons and Ironman triathlons – long considered to be low-intensity, long-duration events – feature periods of intensity above lactate threshold. For competitors, hard efforts are required to drop rivals and build winning margins. Whether you are going for the win or trying to set a PR, you will achieve your best performances in events that feature intermittent high-intensity efforts by optimizing your ability to use all fuels and by providing your body with adequate supplies of all fuels.
Ketosis may prevent gastric distress
On the positive side, athletes in ketosis can perform well at a steady endurance pace, and can do so for many hours while consuming far fewer calories than carbohydrate-dependent competitors. As a result, ketosis may be a good solution for athletes who consistently struggle with gastric distress during ultradistance events. During exercise lasting 9-24+ hours, changes in blood volume, heat stress, and hydration status can slow or halt gut motility. This is a problem when you are consuming large amounts of energy and fluid because food that stays in the gut too long creates the gas, bloating, and nausea that make athletes drop out of races. In fact, GI problems are the leading cause of DNFs in ultramaraton events, so the prevention of gastric distress could potentially make dietary ketosis a reasonable solution for some ultradistance athletes.
For the record, CTS Coach Jason Koop, author of Training Essentials for Ultrarunning, disagrees with me on the paragraph above. He believes strongly that fat adaptation/dietary ketosis is not a good idea for ultrarunners because it is physiologically limiting and because the gut is trainable. He agrees ultraendurance athletes in ketosis might be less vulnerable to GI distress, but points out that GI distress is most often the result of poor planning and inadequate training (both physical and nutritional). In that context, ketosis is a complicated solution to a relatively simple problem, and an ultimately inferior solution in terms of maximizing physiological performance.
Ketosis is very disruptive to training
If carbohydrate is available it is the go-to fuel for muscles and the brain. Only in carbohydrate’s absence will the body transition to producing and using more ketone bodies for energy. This is evolutionary biology. When sugar from plants was available to our ancestors they could gorge on it, use some for energy and store the rest as fat. During times when there were no plants to eat, their carbohydrate stores ran out and they transitioned to ketosis to fuel themselves from their stored fat. To achieve ketosis voluntarily – instead of through inadequate insulin production – you have to essentially eliminate carbohydrate from your diet.
Initially, you will have neither enough carbohydrate nor ketones to fuel your brain. While you are always producing ketones, it takes time (up to 2-3 weeks) for your body to increase production to the point you are relying on them as a primary energy source. During the first week people often experience the “keto flu”, which is not an infection but rather a set of symptoms reminiscent of the flu: Headache, foggy brain, fatigue, irritability, nausea, difficulty sleeping, and constipation. Training performance will definitely suffer (and lifestyle performance may suffer as well). Your power output will be lower than normal. Your running pace will be slower than normal. Perceived exertion will go up, at all intensity levels (this was noted in Burke 2020). Recovery from training sessions will be hindered.
Once you are adapted to fueling yourself primarily on ketones for day-to-day living, you still need to adapt to performing optimally as an athlete fueled by ketones. This can take months, during which time your only progress will be in fat adaptation, not aerobic development, the ability to produce power, or the ability to achieve faster paces.
If you are going to try ketosis as an athlete, the best time to experiment would be a period of general aerobic endurance training. For summertime athletes in the Northern Hemisphere, this typically means fall or winter. It would be a mistake to try making this transition during a period of important, race-specific, high-intensity training.
Weight loss from dietary ketosis is primarily from caloric restriction
Exercise studies of athletes who have adapted to ketosis show they burn more fat at a given exercise intensity than when they were carbohydrate-fueled, but not that they can produce more work (go faster) (Zajac, 2014). When athletes get faster after adapting to ketosis, or even after a period of ketosis followed by a return to an “all fuels” strategy, weight loss is often a big contributing factor to the increase in speed. That’s not a bad outcome, but they lost weight primarily due to caloric restriction. Diets that severely restrict or eliminate food groups cause people to pay a lot of attention to all food choices. This increased focus dramatically reduces mindless eating, and the consumption of junk food, alcohol, and excess sugar. It typically leads to increased consumption of fresh, whole foods. In the case of ketosis, it leads to increased consumption of whole food sources of protein, fat, and vegetables. That’s a good outcome, too, but caloric restriction is still the primary reason people lose weight while following a ketogenic lifestyle. Some of the acute weight loss is also due to the fact you store 3 grams of water with every gram of glycogen stored in muscles. So, less muscle glycogen also means less stored water.
From a performance standpoint weight loss increases VO2 max (milliliters/kilogram/minute), improves power-to-weight ratio, and lowers the energy cost of locomotion. Even if your ability to produce work does not improve, you will go faster and be more economical when you lose weight. (The LCHF group of Burke 2020 experienced a net loss of economy despite weight loss, but it is important to recognize they were elite race walkers with high VO2 max values and low bodyweight to start with. For the vast majority of athletes, modest weight loss will improve economy and increase VO2 max.) What doesn’t matter is whether you lost that weight through ketosis or through other ways of rebalancing caloric expenditure and caloric intake.
Compliance is a major barrier to sustaining ketosis
Advocates of dietary ketosis paint a picture of a glorious carbohydrate-free lifestyle where you’re not hungry as often and don’t suffer from energy fluctuations. From a health perspective, claims include decreased triglycerides, increased insulin sensitivity and reduced symptoms of Type II diabetes, lower blood pressure, slower growth in cancerous tumors, improved cognitive function, and many more.
I have been working with committed, goal-oriented athletes for more than 30 years. I have also witnessed countless diets rise and fall within the general population. We can barely get goal-oriented athletes to stick with an organized nutrition plan – inclusive of all macronutrients – for more than 6 months. In the general population, even people who experience great results with diets like Atkins (low-carb), Paleo (moderate-carb but no refined grains), The Zone (40-30-30) and Ornish (very high carb, extremely low fat) gradually move back toward 45-55% carbohydrate, 15-20% protein, and 25-30% fat within 12-24 months.
Dietary ketosis requires almost complete abstinence from carbohydrate, limiting intake to less than 50 grams (200 calories) per day for most people. And there are consequences for overconsumption, most notably that you kick yourself out of ketosis! Anecdotally, people who indulge in a slice of their kid’s birthday cake, a beer at the ballgame, or a banana in an aid station report feeling terrible afterward. For some, this negative feedback provides greater motivation to avoid temptations that knocked them out of previous diets. For the vast majority of athletes and sedentary people, even with good results the restrictive nature of the dietary strategy is too high a barrier for long-term compliance.
Ketosis is a competitive disadvantage
If eating a banana during a workout or competition will diminish your performance, there’s something wrong with your sports nutrition strategy. That’s not my bias toward sugar talking, but rather 40+ years of experience as an athlete and coach that has shown me that the best prepared athletes are those who are the most adaptable. To be a successful athlete you have to be able to perform using the fuel available and the equipment you have, in the environment provided. Courses change at the last minute, aid stations run out certain foods, your support crew can get lost, or your special food can fall out of your pocket. If you can’t immediately change your strategy to match the reality of your situation, you are at a competitive disadvantage.
Ketosis will be corrupted (already happening)
There may be some merit in a LCHF diet for disease prevention/mitigation, and it can be a lifestyle that promotes the consumption of whole foods and very little packaged food. But can the most vulnerable populations that would benefit most stick with it? If Atkins was too hard to stick with in its original form (more protein, fat, and fresh vegetables; less sugar and processed food) and was rapidly corrupted by packaged food manufacturers, how is it realistic to expect the overweight and/or chronic disease populations to adopt and stick with a much more intensive strategy?
Experience also tells me nutritional ketosis will be corrupted by supplement and packaged food industries the same way Atkins, Paleo, Zone, and other have been. The common pattern linking the rise and fall of popular named diets begins with a strategy that focuses on whole foods and somehow restricts energy intake. The strategy works, people feel great and lose weight. Foods and supplements are developed to make compliance more convenient, but these shift people back to old habits of consuming fewer whole foods. The packaged foods and supplements contribute to increased caloric intake, people regain weight, and once the positive results have disappeared their compliance diminishes and they return to their normal food choices and eating behaviors. As soon as you see “keto-cookies”, it’s over.
Exogenous Ketone Supplementation
From a sports science perspective, exogenous ketone supplementation was the most promising development from this round of high-fat science (this isn’t the first time LCHF has come along). Ketone esters have made it possible to consume ketones in a drink or food and significantly reduce the time necessary to achieve dietary ketosis. They also made the idea of “dual fueling” a compelling idea, in that an athlete could potentially supplement with exogenous ketones and thereby conserve limited carbohydrate stores for high-intensity efforts (Cox, 2014). This supports the fundamental sports science tenant of using training, nutrition, and recovery to maximize your body’s capacity to do work.
Unfortunately, current research indicates exogenous ketone supplementation is rarely effective as an ergogenic aid. In an opinion published in the December 2019 issue of Sports Medicine, David Shaw et al. state: “No beneficial performance effects during high-intensity exercise have been demonstrated following the ingestion of exogenous ketone supplements that increase blood D-β-hydroxybutyrate concentrations up to ~ 1 mM. Racemic ketone salts and BD (1,3-butanediol) exert no effect on oxygen uptake, blood glucose concentration, lactate accumulation, or RPE at exercise intensities > 70% VO2max, and demonstrate no or negative effects on performance.”
That said, Tour de France teams and national teams have been purportedly utilized ketone supplements on and off over the past several years. Cyclingnews.com examined the use and evidence for efficacy in early 2020. It seems the benefit, if there is one, may be related to recovery during long blocks of racing or training. The cost, however, is still prohibitive for most athletes.
Manipulating Carbohydrate Availability
Matching carbohydrate availability to training goals is a strategy that has been used successfully by amateur and professional athletes for a long time. There are various protocols for it, including “Sleep Low” (Marquet, 2016), but the basic idea is to complete high-intensity intervals and important competitions with high carbohydrate availability. During endurance or general fitness training, exercising with low carbohydrate availability can enhance weight loss and improve the body’s ability to metabolize fat for energy. I’ve written about Train Low before, and it’s a strategy supported by several of the sports scientists I respect, including Louise Burke. In the aforementioned 2020 study of racewalkers, there was a third group that utilized a “Train Low” carbohydrate availability method, and their end-of-camp performances were better than the LCHF group and not as good as the HCHO group.
So there you have it, at least for now. Sports science continues to develop and it is important to be open to new ideas and evaluate them on their merits. If you want to lose weight, ketosis or LCHF works. If you want to train effectively, a mixed diet with high carbohydrate availability for important workouts and competitions is your best bet.
CEO/Head Coach of CTS
Pro Coach and co-author The Time-Crunched Cyclist and Training Essentials for Ultrarunning
References and Suggested Reading:
Burke, Louise M et al. “Crisis of confidence averted: Impairment of exercise economy and performance in elite race walkers by ketogenic low carbohydrate, high fat (LCHF) diet is reproducible.” PloS one vol. 15,6 e0234027. 4 Jun. 2020, doi:10.1371/journal.pone.0234027
Burke, Louise M., Megan L. Ross, Laura A. Garvican-Lewis, Marijke Welvaert, Ida A. Heikura, Sara G. Forbes, Joanne G. Mirtschin, Louise E. Cato, Nicki Strobel, Avish P. Sharma, and John A. Hawley. “Low Carbohydrate, High Fat Diet Impairs Exercise Economy and Negates the Performance Benefit from Intensified Training in Elite Race Walkers.” The Journal of Physiology (2016).
Burke, L. M. “”Fat Adaptation” for Athletic Performance: The Nail in the Coffin?” Journal of Applied Physiology 100.1 (2006): 7-8.
Burke, Louise M. “Re-Examining High-Fat Diets for Sports Performance: Did We Call the ‘Nail in the Coffin’ Too Soon?” Sports Medicine 45.S1 (2015): 33-49.
Cox, Pete J., and Kieran Clarke. “Acute Nutritional Ketosis: Implications for Exercise Performance and Metabolism.” Extreme Physiology & Medicine. BioMed Central, 2014.
Cox, Peter J., Tom Kirk, Tom Ashmore, Kristof Willerton, Rhys Evans, Alan Smith, Andrew J. Murray, Brianna Stubbs, James West, Stewart W. Mclure, M. Todd King, Michael S. Dodd, Cameron Holloway, Stefan Neubauer, Scott Drawer, Richard L. Veech, Julian L. Griffin, and Kieran Clarke. “Nutritional Ketosis Alters Fuel Preference and Thereby Endurance Performance in Athletes.” Cell Metabolism 24.2 (2016): 256-68.
Havemann, L. “Fat Adaptation Followed by Carbohydrate Loading Compromises High-intensity Sprint Performance.” Journal of Applied Physiology 100.1 (2006): 194-202.
Marquet, Laurie-Anne, Jeanick Brisswalter, Julien Louis, Eve Tiollier, Louise M. Burke, John A. Hawley, and Christophe Hausswirth. “Enhanced Endurance Performance by Periodization of Carbohydrate Intake.” Medicine & Science in Sports & Exercise 48.4 (2016): 663-72.
Pinckaers, Philippe J. M., Tyler A. Churchward-Venne, David Bailey, and Luc J. C. Van Loon. “Ketone Bodies and Exercise Performance: The Next Magic Bullet or Merely Hype?” Sports Medicine (2016).
Shaw, D.M., Merien, F., Braakhuis, A. et al. Exogenous Ketone Supplementation and Keto-Adaptation for Endurance Performance: Disentangling the Effects of Two Distinct Metabolic States. Sports Med 50, 641–656 (2020). https://doi.org/10.1007/s40279-019-01246-y
Volek, Jeff S., Daniel J. Freidenreich, Catherine Saenz, Laura J. Kunces, Brent C. Creighton, Jenna M. Bartley, Patrick M. Davitt, Colleen X. Munoz, Jeffrey M. Anderson, Carl M. Maresh, Elaine C. Lee, Mark D. Schuenke, Giselle Aerni, William J. Kraemer, and Stephen D. Phinney. “Metabolic Characteristics of Keto-adapted Ultra-endurance Runners.” Metabolism 65.3 (2016): 100-10.
Zajac, Adam, Stanislaw Poprzecki, Adam Maszczyk, Milosz Czuba, Malgorzata Michalczyk, and Grzegorz Zydek. “The Effects of a Ketogenic Diet on Exercise Metabolism and Physical Performance in Off-Road Cyclists.” Nutrients 6.7 (2014): 2493-508.
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If Keto is so bad why how was Chris Froome able to win the Tour de France while training on Keto? Check out this site: https://www.compeatnutrition.com/tour-de-france-nutrition/#:~:text=Subject%20to%20massive%20media%20scrutiny,period%20between%202007%20and%202013.
I’ve been on a ketogenic diet for over 15 months and I did so because of a spinal cord injury that led me to reduce my 4-5 day heavy lifting routine to a light walking/biking/physical therapy routine. I’ve noticed that I can go in and out of ketosis very fast because of adaptation. I was on a strict LCHF diet for the first six months and then moved to having carbs on 1 or 2 days a week. At this time, I’ve started to use carbohydrates and the insulin surge from them after workouts. Do you have any knowledge of any studies on the affects of training the body to increase its glycogen stores through this kind of metabolic manipulation? I have a background in biochemistry and was a trainer in my youth, and I have been trying to work on an adaptive approach to maximizing glycogen stores for older individuals with disabilities such as mine. The other reason for my change in diet was to increase the effects of medications and reduce the need for larger dosages, which I have noticed from switching to the ketogenic diet. The most effective anti-inflammatory medication has been switching to this diet, since diets high in carbohydrates are highly inflammatory unless your an athlete whose body is a well oiled machine. I think that most people think that this diet is a fad, but it’s more of a natural metabolic state than being bombarded with sugars all day long and creating an environment where the body has to continually be in motion to control this or fast. I think that being able to control the bodies metabolism is better on the bodies joints than increasing hours of running etc. I think that when athletes look at the benefits of this dietary approach is more realistic as we age than peak performance. I have also used this approach with other non athletes and the outcomes are more consistent than a calorie counting approach, at least initially. Fats create a longer feeling of satiety than other macronutrients and they reduces feelings of depression and anxiety that low fat high carb diets are plagued with. I’m not saying that high carbohydrates when training for an endurance event isn’t beneficial, but that it is limited to the athletes in sports where maximal intensity exertion is needed. For the rest of the human race in this modern low effort world we’re all living in, the ketogenic diet is a godsend and when done in a way that teaches the individual more control over their metabolic pathways the better the outcome. I have been part of many lifestyle transitions where a calorie counting approach was used with a 40:30:30 macro ratio, the client almost always had too much prep-work that the diet wasn’t a sustainable lifestyle. So, if performance is key, by all means use the carbohydrate intake recommendations used by the USADA for “Olympic” athletes. But, if you’re aging and are limited in the workouts you can do, start a ketogenic diet that resets your insulin sensitivity and then add in carbohydrates after workouts until you find the amount of carbohydrate that your individual body can handle before it starts to kick you out of ketosis. This way you at least have control over your weight, endurance, and have a lower ROS to heal faster. I think the bias here isn’t looking at the benefits of being able to use different regimens in ones dietary tool box. I hope that you can at least look at the benefits of both types of training lifestyles to be able to create a metabolic machine instead of one that is so dependent on carbohydrates alone for athletic endurance training.
Hi Chris, my husband and I have been eating LCHF (not strictly keto) but no sugars, no grains for almost 2.5 years now. I am 56 and my husband is 60. We are avid cyclists. We are happy on our diet we enjoy being free of the sugar addiction and not taking in all the poisons in the grains. I have not lost weight ( I did initially and then went back to my post menopausal weight that I reached on carbs.)( I cycle better at this weight though it has slowed me down on the climbs(power/weight)(I’m built more like a sprinter than a climber anyway, my husband is stable on his weight (he’s tall and thin and can climb(He can stand for ages on a climb and climb away from me. I can stay with him when he sits and I sit). He is more in ketosis than I am. We both take on more carbs during long distance events, for instance bananas, vegan christmas cake, more fruit. What we’re interested to find out is how does one introduce more carbs (e.g. how many days before, what kind of carbs and how much) to be able to perform better at HIIT for a race or a training week with HIIT, is that possible? Kind Regards
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Keto is like removing RAM from my laptop and just working with the HD. Why we need to remove a energy buffer? What will be the next, the phosfocreatine buffer?… it’s exactly the opposite, the more buffers the better, at least for performance.
Excelente articulo, muy completo 🙂
The problem with being Keto and then deciding on race day to eat carbs, is that your body has actually downregulated its ability to use carbohydrates. Even if the glycogen is available. Also, you’ve not trained your gut to absorb carbohydrates in training. This, is a recipe for disaster, in my opinion.
As mentioned in the article and the comments, fat oxidation for energy has a different oxygen requirement than carbohydrate oxidation for energy.
Is it equitable to compare the VO2 max for individuals using different energy systems?
I’d like to understand if/how VO2 max for a given performance level varies with, or correlates to, the primary energy source.
One of the best articles I’ve read on the subject, encompassing the most current science. As a cycling and certified nutrition coach, I see that keto seems to be a little bit like a religion for some people – those who will faithful follow it by finding an angle (not representative of the whole) that supports their belief. After all, each person creates their own “reality”.
Being lean and strong/fast is hard work – it requires a lifestyle that many are not willing to have. So hard in fact, that these diets gain popularity so quickly.
Just look at the joint position statement by the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine published in the journal Medicine and Science in Sports and Exercise – and read what they have to say about carbs and performance (link below).
For the women athlete, I highly recommend the book The Exercising Female: Science and Its Application (Routledge Research in Sport and Exercise Science)
I am not a scientist or a coach. I have read many endurance books. I read about and gave the keto diet a try believing it would help. I was able to cycle at a normal speed for me for 2.5 hours on only water. However, as time went on my performance suffered. Reluctantly I gave up on the keto diet. I am a nobody. But it does not work for me. My biggest claim for fame was doing 511 miles on the bike in less than 48 hours unsupported at age 66. I did this on a high carbo diet. Thanks for your article.
No comment on using ketosis to lower VLAMAX?
As always. Thanks much!! It’s great to hear a good scientific thorough perspective in this day and age of YouTube entertainment content with half baked side by side comparisons on the same topic (I’m not pointing fingers at any one GCN)…
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Would like to see a similar analysis on intermittent fasting options and effect on performance. great blog posts
We ran a small study on three of our 140.6 athletes going into their second season. We saw that while Keto did seem to help on the shorter 70.3 B and 100 mile bike C races, the longer 140.6 performances were effected across the board.
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I completely disagree. I am an indoor cycling instructor and avid half marathon runner who has seen my level of performance/speed/endurance increase substantially on my 6 months of modified keto diet. I am currently training for a 200 mile bike race in August, and my only concern is what types of food I can carry that are keto friendly that will sustain me.
From what I’ve heard from other keto-adapted long distance athletes, you will need to carry much less than if you were burning carbs for 200 miles. And maybe even just one snack to sustain you half way through because the energy stores you are pulling from are 20x greater than the glucogen stores your competitors are using. Good luck!!
It took me 2 years to realize keto was slowing me down. I was also all excited at 6 months.
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‘As soon as you see “keto-cookies”, it’s over. ‘
Today was the day – I saw the keto-cookies.
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Many articles such as this are well informed but also seem to bash ketosis because it is not perfect. But for every point made about the problems of ketosis, using the same attitude can be said about the problems of eating a high carb diet.
There is no greater glut of products out there than high carb junk.
Ketosis can be targeted and definitely a banana or a carb meal can be used around training time
Ketosis does not have to be 24 hrs a day in order to reap the benefits. It is training the body to run on fat most of the time and have better access to the fat we all carry.
Once an adaptive phase is complete, it is absolutely reasonable to train other systems as well.
If we took the same attitude with high carb diets, in particular the negative side effects of food, health in
the general population , likely that article would have to be longer
high-carb diets do not automatically mean junk carbs… although that can easily be assumed. For athletes, junk carbs are definitely not what they want to be putting into their bodies.
High carbs from whole foods like any and all fruits, vegetables, legumes, grains are the right kinds of carbs to intake which include healthy amounts of fiber and nutrients. That’s the correct way to do high-carb. Not from junk foods like cupcakes, donuts, potato chips, french fries, or even white bread and white rice etc. – absolutely not. confusing this is very common.
What about age groups and the injury recovery effect
The massive rise in diabetes in athletes and youth doesn’t mention causes from the keto diet
Most pioneer drafts on the subject always head towards quality carbs consumption in small values .
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I rewrote your article from my perspective…
Why Every Endurance Athlete Should Go Keto
When it comes to weight loss and endurance performance, dietary ketosis is the strategy everyone is asking about this year. On the surface, ketosis or a ketogenic diet offers everything an endurance athlete could dream of: endless energy, freedom from bonking, and an efficient pathway to weight loss. The diet has been all over mainstream magazines, it’s the subject of several new books. So, is it time for cyclists, triathletes, and runners to go Keto?
First, a refresher course on what a ketogenic diet is. It is a diet where your body produces ketones. The actual number of carbohydrates depends on the person. Some people make ketones with 200 grams of carbohydrates per day, some are required to limit their carbohydrates to less than 20 grams per day. Your fasting insulin and glucagon levels determine the point where the body makes ketones.
It’s appealing to athletes because we have a virtually unlimited reserve of fat calories to pull from but can only store 1600-2000 calories worth of carbohydrate in muscles, blood, and the liver. An athlete fueled by ketones would be theoretically “bonk-proof”, since bonking is the result of running low on blood glucose.
Dietary ketosis for athletes is one of the most hotly contested subjects right now. Proponents point to the metabolic advantage of relying on fat instead of carbohydrate, and critics point out the physiological limitations of eliminating carbohydrate as a fuel for performance. You’ll find bias in both groups, either because scientists and coaches have been in the high-carbohydrate camp for many years. I followed the high-carbohydrate recommendations when I started endurance sports. It nearly ruined my health. May are still on the high-carbohydrate bandwagon, mostly because there’s a lot of money to be made by supplements companies that would lose quite a bit of money if cheap carbohydrates were not used so extensively in endurance sports.
Here’s what I have learned:
The body’s ability to make and use ketones is a decided advantage for the health and performance of any athlete. Athletes are best served by training the body to use fat as its primary source of fuel and to add in carbohydrates only as a supplement to boost performance.
Athletes are better served by prioritizing insulin sensitivity in order to maximize fat oxidation rates to improve health and performance outcomes.
And here’s why….
Increased Fat Oxidation Rates IMPROVE endurance performance.
The study Ken Hetleid highlights the benefits of increase fat oxidation. The study highlights the performance differences between high performing and recreationally trained athletes. The differentiator is their rate of fat oxidation rates. In order for the body to perform well at oxidizing fats it needs to be efficient at burning fat as a primary fuel source. Despite similar rates of perceived exertion (RPE), blood lactate and carbohydrate oxidation rates, the better performance by the well trained group was explained by their nearly threefold higher rates of fat oxidation at high intensity.
What is Ketosis?
What is ketosis anyway? In human beings and most other mammals, acetyl-CoA formed in the liver during oxidation of fatty acids may enter the citric acid cycle or it may be converted to the “ketone bodies” acetoacetate, D-β-hydroxybutyrate, and acetone for export to other tissues. Acetone, produced in smaller quantities than the other ketone bodies, is exhaled. Acetoacetate and D-β-hydroxybutyrate are transported by the blood to the extrahepatic tissues, where they are oxidized via the citric acid cycle to provide much of the energy required by tissues such as skeletal and heart muscle and the renal cortex. The brain uses acetoacetate or D-β-hydroxybutyrate.
It is a pretty handy process. Even the very leanest athlete has about 20 times the amount of energy stored in the form of fat than it does as a glucose dependant athlete. The most efficient athletes can store 2,000 calories of glycogen that needs to replenished frequently, especially if they are not well adapted at tapping into their fat stores.
Why Use Carbs?
The process of using ketones seems great, why do we use the carbs? One reason carbohydrates are emphasised is that there is a process of adaptation to using fat as the primary source of fuel. During this process, a typical athlete’s performance will suffer for 4-12 weeks before it comes back to baseline performance. Most endurance athletes are addicted to carbohydrates and the idea of giving them up seems terrifying.
Another reason for the resistance is the idea that carbohydrates are the primary source of fuel for high intensity exercise. But is that true? In the findings in the above mentioned study show that we don’t actually stop burning fat once we hit lactate threshold. Their bodies produce lactate at certain thresholds.The higher lactic acid induced production of CO2 [through HCO3- buffering] has a large influence on the calculation of carbohydrate and fat oxidation. It creates an overestimation of the carb burning amount and an underestimation of the fat burning. The estimation of fat use with these equations goes so low in fact that it often becomes zero, and then negative. Of course you can’t have a negative negative for fat oxidation, so scientists typically misrepresent present their data because they don’t understand the limitations of the test.
Ketosis prevents gastric distress
Athletes in ketosis can perform well at a steady endurance pace, and can do so for many hours while consuming far fewer calories than carbohydrate-dependent competitors. As a result, ketosis may be a good solution for athletes who consistently struggle with gastric distress during ultra-distance events. During exercise lasting 9-24+ hours, changes in blood volume, heat stress, and hydration status can slow or halt gut motility. This is a problem when you are consuming large amounts of energy and fluid because food that stays in the gut too long creates the gas, bloating, and nausea that make athletes drop out of races. In fact, GI problems are the leading cause of DNFs in ultramaraton events, so the prevention of gastric distress could potentially make dietary ketosis a reasonable solution for some ultra-distance athletes. This is a key benefit of keto-adaptation. Ultra-endurance athletes are able to compete at a higher rate without shutting down their stomachs is a key benefit of keto-adaptation.
Ketosis is not disruptive to training
If you have trained your body to use fat as its go-to fuel for muscles and the brain the absence of carbohydrates is not a problem. This is evolutionary biology. Sugar from plants was not readily available for most of our ancestors for millennium. You don’t see cave paintings of farmers.
If you spend a couple of months during the off season to adapt to using fat as your primary source of fuel you can add in carbohydrates during training and racing occasionally and remain keto-adapted. The key is to keep glycogen stores partially empty. Doing a weekly fasted workout, warming-up fasted and reverting to a ketogenic diet after workouts. This will ensure that your body will continue to produce ketones. During this period, your performance will continue to improve, your health and lifestyle with increase, and your power outputs will continue to rise. Since ketones are a clean burning fuel you will generate less reactive oxygen species. Your recovery will be dramatically improved.
Once you are adapted to fueling yourself primarily on ketones for day-to-day living, you will find out how easy it is to to maintain a high level of fat oxidation and ketone production.
Weight loss from dietary ketosis is primarily from fat and lean mass is preserved
Exercise studies of athletes who have adapted to ketosis show they burn more fat at a given exercise intensity than when they were carbohydrate-fueled, but not that they can produce more work (go faster) (Zajac, 2014). When athletes get faster after adapting to ketosis, or even after a period of ketosis followed by a return to an “all fuels” strategy, improved fat oxidation and weight loss is often the biggest contributing factor to the increase in speed. Even though dietary changes are necessary to maintain keto-adaptation most athletes find the improved performance worth the adjustment.
From a performance standpoint weight loss increases VO2 max (milliliters/kilogram/minute), improves power-to-weight ratio, and lowers the energy cost of locomotion. Typically, athletes who increase their fat oxidation will also see increases in VO2 max. Power typically improves as well. This is a nice combination if you want to go faster and be more economical.
Compliance is not a major barrier to sustaining ketosis
As discussed earlier, using carbohydrates strategically ensures an athlete stays in dietary ketosis. Depending on the period of training the athlete is in it is easy to manage a low carbohydrate/ketogenic diet while training. From a health perspective, studies show that decreased triglycerides, increased insulin sensitivity and reduced symptoms of Type II diabetes, lower blood pressure, slower growth in cancerous tumors, improved cognitive function, and are some of the many benefits of becoming keto-adapted.
Dietary ketosis does not require a complete abstinence from carbohydrates. It is a matter of figuring out your personal limits. Learning how to train to deplete your glycogen stores will help ensure that you are never kicked out of ketosis. The way an athlete trains to maintain ketones ensures that they will not destroy their program is they indulge in a slice of their kid’s birthday cake, a beer at the ballgame, or a banana in an aid station. Learning how your body responds is the way to maintain the health and performance benefits of keto-adaptation. For the vast majority of athletes and sedentary people, the good results of being keto-adaptation is worth the effort.
Ketosis is a Competitive Advantage
Athletes who have taking the time to become keto-adapted have seen huge increases in their fat oxidation rates. This has led to stellar performances in ultra-runners like Zach Bitter, Cyclist like Roman Bardet, and triathletes like Terenzo Bozzone have seen stellar performances by increasing their fat oxidation rates.
Exogenous Ketone Supplementation
One of the best benefits of being keto-adapted is the lack of external fuel sources. A typical keto-adapted athlete consumes less fuel of all forms during training, including water. Some athletes choose to use exogenous ketones. Although this might have some benefit in the form of providing extra electrolytes to the athlete, exogenous ketones are 100% not necessary.
Manipulating Carbohydrate Availability
Matching carbohydrate availability to training goals is a strategy that has been used successfully by amateur and professional athletes for a long time. There are various protocols for it but the basic idea is to follow Maximum Aerobic Function (MAF) heart rate protocols until well keto-adapted. During endurance or general fitness training, exercising with low carbohydrate availability can enhance weight loss and improve the body’s ability to metabolize fat for energy.
CEO/Head Coach of KetoEndurance
Good work Stephanie!
Thanks for your reply! 🙂
Thank you, Stephanie! Exactly what I thought. I couldn’t help but read the original article and think about Zach Bitter winning a 100-miler in 13 hours without consuming a single energy gel or drink.
Nearly everything Chris & Jim say is so wrong! Keto being a competitive disadvantage, not helping for endurance performance, being physiologically limiting – all of it is absolutely unfounded, no matter how many citations they add afterwards. They should be ashamed of still calling themselves coaches while peddling information that will limit their coachees’ performance.
I had a big smile on my face after reading your rewriting of the article.🤓
And if you face the race with the mind of David Goggins … you will blow the high carb competition outta the water eating keto/carnivore 😉
I’m betting you could add some glucose into your blood by eating high amounts of whey protein isolate or small amounts of raw unpasteurized honey for sprints or uphill portions of the race.🤷♂️
I love how you threw his bias back in his face. LMFAO
I had done keto before when I was in great physical shape and training 4-5 days a week in mainly in anaerobic workout with small 20-30min of aerobic exercise on top. I did see a reduction in output, but the affects it had on my health were phenomenal. I have my B.Sc. in Biochemistry and have worked in the field of training athletes and your normal obese American that is addicted to a high carb diet that is killing them. So, when people throw out these articles that are full of bias instead of a well thought out comparative conceptual article with the benefits of both to let the reader to decide what’s best for them.
My story is that when I reached the age of 39, my body started to see some serious medical issues where I had to have my hip replaced and I had developed degenerative disc disease with a spinal cord disease as well. This made it impossible to train the way I had for the last 25 years and so I couldn’t manage my weight through building larger muscles to offset my caloric intake. I had also been put on opiate pain killers to manage the pain that almost led to me taking my own life. In fact this diet saved me.
I had noticed that the ketogenic diet that I was on earlier, before my surgeries, made it possible to decrease the amount of medication needed to produce the affect needed. I wasn’t on the painkillers at that time, but the other medications like antidepressants were reduced to the minimum dosage needed to be effective. Knowing this I started a ketogenic diet and violà my need for increasing amounts of pain medication stopped. Along with the reduction of medication to illicit an effect, my inflammation was reduced so much that my wedding band size had dropped from an 11 to a 9.5. I think that many people look at this as a diet to lose weight, but they are so wrong.
This lifestyle reduces all inflammatory processes involved in the metabolism of glucose from glycogen stores and blood glucose. This is part of the reason that they are studying the use of a ketogenic diet during cancer treatments as opposed to fasting. I can go on and on about how this lifestyle has made my life better, but I won’t. What I will do is talk about how my body has adapted to prefering ketones over glycogen for it’s fuel source. I have implemented a 1 to 2 day a week carbohydrate full day to my diet, mainly to increase the conversion of T4 to T3 to maintain a healthy metabolism. I’m in more control of my bodies metabolism than I have ever been and I don’t have to count calories to lose weight, I just eat smaller portions and increase my activity. It’s so much easier to control cravings and stop snacking through this regimen. Anyways, I appreciate the rebuttal because so many people are stuck in the old ways of eating.
You are spot on with the insulin problem. Carbs are not required in our diet but are needed by the brain and some organs even after adaptation. I am a 59 y.o. 150 watt recreational road bike and recumbent rider. I eat healthy, but include carbs, off the bike. On the bike it is always an empty stomach and water only. If you have a healthy liver and you have been riding long enough clean on water (and electrolytes) only you will quickly transition into ketosis when glycogen is low on the ride.
For myself, I come home from a 60-100 mile ride with a normal glucose level (70-90 mg/dL) and in ketosis (~1.5 mmol/L) and after some catch-up hydration it takes about 3 hours to get hungry. On longer slow rides you will waste away if you do not eat enough, but that is unlikely in our world of gluttony. So using this method my A1C resides at 5.1 which translates to about an average glucose level of 83.5. My take-away is that I can eat healthy with carbs, ride blissfully without them, and still maintain vascular health. Without carbohydrate restriction and supplemental carbohydrate reducing aerobics, my red blood cells would be highly glycated and I would be on a path to insulin gut, diabetes, heart disease and more.
You inspired me to go ride the “Hotter than Hell 100” but I will not push harder than 150 watt on average. More fun that way.
are you eating your carbs primarily after your ride ? what are your carb sources, out of curiosity.
interested in learning more…
Bill, I’m interested to know if you’re diabetic? I am a type 1 diabetic, recently taking up lots of mountaineering and more endurance-oriented activities. I’m considering switching to a keto diet to fuel these, to avoid the complications that come with administering insulin (in response to carbs) while exercising. Changing activity levels drastically changes my short term insulin sensitivity and it cause a lot of both low and high blood sugar situations).
If you are Diabetic, I would love to know your thoughts!
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Good overall read about keto. I do think that too many people jump right into the diet though which may cause GI issues. I’m often a fan of ramping up my fat intake slowly but really good read.
So what do you eat before performing?
Start with basic caloric needs to ask this question. But for me I eat two eggs (change it up during training: boiled scambled, sunny up) with bread, spinach or kale, meat protein, fruit and cheese. Starbucks protein plate in a pinch works out for a pre race meal. Inifinit nutrition, for overall race and if there are hills, supplement with a bar that changes things up for your gut. I used this method for my first Ironman; worked well enough: 11hrs-57min-59sec (1:13 swim; 5:45 bike, 4:40 run). On the run I felt that I supplemented well, but ran out of Infinit at mile 18. Drank gatorade during training for this event and endured the mishap. Ate half a banana, two licks of BASE salt to help with finish line “no cramps” look and helped my recovery.
Awesome post!I love the idea.Thank you for the valuable information on this tips.
The problem with being Keto and then deciding on race day to eat carbs, is that your body has actually downregulated its ability to use carbohydrates. Even if the glycogen is available. Also, you’ve not trained your gut to absorb carbohydrates in training. This, is a recipe for disaster, in my opinion.
He is talking about professionals, high performance athletes! The ones who ride 100 milles in 4 hours ….so this is not really aply to your 5k run in 29 min. You can do that with no carb, ZERO carb, ZERO nothing …
I ride 100miles in 4 hours. I’m 58 and not a professional. I’m open to new ideas so tried the keto approach and can endorse all of the conclusions in this article.
Still it is worth citing professionals. For them being the best is not just a matter of ego, it’s literally a matter of life and death: at least to the point where if they fail they will not live the life they aspire to. The risks they take to both health and reputation by doping are a clear example of this. If keto had any benefits then some professional athletes at least would be early adopters. In fact, to the best of my knowledge, not a single one is. To the contrary those professionals who have experimented with keto have found their performance deteriorates rapidly.
Keto is good if your objective is to do ultra events where duration means the vast proportion of your calories will come from fat in any case and the power demands are low and consistent.
For everything else, if optimum performance in terms of time is your goal, then a balanced approach to nutrition is best.
I call Bs on you riding 100 miles in 4 hours?? you mean you average 25 mph for 4 hours
you have no idea who martin is – why would you assume any random person is lying ? he’s telling you he rides 100 miles in 4 hours. plenty of people do that. look up Ironman race times.
Look up Dan Plews AG win at Kona in 2018. He backs his win up with actual science, not CTS misinformation. Too bad the many many years that Chris has been in the coaching business has made him narrow minded and sucking up to the carbo maffia!
Wow! What a contentious topic! I am a firm believer that everybody’ bodies are a little different. There is no way to prescribe one nutrition plan that will work for everyone. For me, personally, I do better with a lower carb diet (not keto low, though) with most of my carbs coming from vegetables and a few whole grains thrown in. I was diagnosed with Type II diabetes when I was 30 and have managed to control it through diet and exercise, but my body still reacts to sugars a little differently than then next person. My body doesn’t handle sugar or white flour very well at all. The good news is that carbs from vegetables and grains usually are more wealthy in nutrients, which is good for how everything runs and performance.
So, I don’t quite get it. I’m a CTS athlete – a 50 year old age-group triathlete – and I rely on this site among others for good training advice. I’m a happy ketoer – sugars, carbohydrates from grains are sources of both addiction and inflammation for me. While your article is well-sourced it mostly promotes broad, negative viewpoints of LCHF … just review the subheadings … “limiting”, “very disruptive”, “major barrier”, “corrupted”. I get that on raceday sugars are king for fueling but many many people thrive on this type of diet for the remainder of year. That means they reach the starting line happier and healthier. I would think that when your website says “Guiding and Inspiring Athletes From Every Walk of Life to Better Performance” that would include advice that understands that every individual responds differently to diet, and that blanket advice is not that helpful. Cheers, Brad.
I think that some “pro-” keto or whatever tend to get draconian and dogmatic about diets. Actually, I think diets become like religious practices that are impossible to keep – unless that is how you make your living (e.g. clergy, monks, nuns, etc.). Professional athletes and elite amateur athletes are typically positioned with support systems that will enable them to train, sleep, and nutritionally support themselves for any goal or set of goals. One thing I have gotten out of LCHF (having genetics for insulin resistance issues) is more metabolic flexibility. If one is “addicted” to cabs or having roller-coaster blood sugars and energy problems, keto/LCHF is a way to re-correct the problem. But it needs significant vitamin and mineral support. The problem with getting “religious” about training, diet, or even self-help attempts is the problem with extremes. One must push to an extreme here and there to get the adaptive processes to work. But one also needs to work on his or her homeostatic set points. That means, eat, train, and sleep within a degree of their personal normal frequently.
Just my 2 cents.
I agree with you; this was a heavily biased article from the beginning. Even in the early paragraphs, it’s obvious:
“You’ll find bias in both groups, either because scientists and coaches (including me) have been in the high-carbohydrate camp for many years, or because there’s a lot of money to be made by creating a market for new media and supplements around a new high-fat dietary strategy. I recognize my historical bias toward carbohydrate, but have tried to look at the science objectively.”
Really? ‘a lot of money to be made’ is why there might be bias in one group? Not because maybe the lifestyle works (as is obvious for many people)? And not much money to be made by marketing glucose drinks and electrolyte products, etc for carb-based athletic performance?
I found the whole article, while interesting, to be grotesquely slanted and presented as though keto is merely a flawed dietary regime, even while admitting its massive and multiple health benefits for many people. How can a thing that is so good be so bad? Unless you come at it with ingrained bias, of course.
He quotes one coach who disagrees with keto as a dietary regimen during training. Aren’t there some out there who favor it? Why are they not represented? Coach Koop believes keto is not an option because he believes the gut is trainable; and yet
“In fact, GI problems are the leading cause of DNFs in ultramaraton events, so the prevention of gastric distress could potentially make dietary ketosis a reasonable solution for some ultradistance athletes.”
If the gut is so trainable, why are GI problems such an issue?
Also, this statement is patently false:
“To achieve ketosis voluntarily – instead of through inadequate insulin production – you have to essentially eliminate carbohydrate from your diet.” Depending on the individual, the body can tolerate a certain amount of carb and still remain in ketosis.
Also, this is surprising:
“Initially, you will have neither enough carbohydrate nor ketones to fuel your brain.”
What does that even mean? Does the brain starve during this time? It certainly is shocking. I have images of all the brain-dead keto-ized zombies walking around. Oh, wait… that’s not actually a thing…
And this bit:
” While you are always producing ketones, it takes time (up to 2-3 weeks) for your body to increase production to the point you are relying on them as a primary energy source. During this period, training performance will definitely suffer (and lifestyle performance may suffer as well).”
The negativity goes on. Since when did an athlete ever say, ‘Oh, if I have to wait 2-3 whole weeks for an improvement, my training is meaningless, I’m not going to invest that much time in something that will take *that long* and oh, my lifestyle performance may suffer as well? Yikes!’
“Your power output will be lower than normal. Your running pace will be slower than normal. Perceived exertion will go up, at all intensity levels. Recovery from training sessions will be hindered.”
You left out “and your breath will smell and you’ll have trouble finding a mate”.
The negative slant is not unexpected, of course, as the author readily admits to it, but to me it seems like it’s a barely contained rant and goes on and on and on.
Obviously keto is not for everyone. But then, nothing is (not even using carbs for fuel – look at cultures around the world whose diet more closely resembles that of keto).
The author presents a number of things as something to be surprised at, but this only shows that he is unaware of certain aspects of the diet, or that he overvalues certain carb-related regimes and undervalues the corresponding keto regime for the same thing:
“Weight loss from dietary ketosis is primarily from caloric restriction”
That shouldn’t be much of a surprise. When one is consuming a fat-based diet, the energy and nutrition gained is more satisfying and longer-lasting, resulting in the unsurprising need for fewer calories. Part of the beauty of a keto based diet, is, in fact, how easy it is to adhere to. Cravings are greatly reduced because the body is not constantly being put into a state of WANT.
“I have been working with committed, goal-oriented athletes for more than 20 years. I have also witnessed countless diets rise and fall within the general population. We can barely get goal-oriented athletes to stick with an organized nutrition plan – inclusive of all macronutrients – for more than 6 months.”
Why is that an indictment against a keto diet? If you can’t even get people to stick with what you believe to be an optimum, organized nutrition plan, how does it follow that a different plan is worse?
and When you say “In the general population, even people who experience great results with diets like Atkins (low-carb), Paleo (moderate-carb but no refined grains), The Zone (40-30-30) and Ornish (very high carb, extremely low fat) gradually move back toward 45-55% carbohydrate, 15-20% protein, and 25-30% fat within 12-24 months.”
As though the fact that people go back to carbs after a year or two of keto proves that the diet is pointless, you are probably missing something important: that perhaps those people may have lost the weight that they were hoping to lose, and so moved back to what is undeniably an easier diet to adhere to, if only because a carb-based diet, being what’s currently on offer, is simply easier to access.
“Anecdotally, people who indulge in a slice of their kid’s birthday cake, a beer at the ballgame, or a banana in an aid station report feeling terrible afterward.”
Because the population has been told for 70 years that carbs-are-good and fat-is-bad, is it any surprise that what you might find on offer, anywhere you look, is cakes and fruits and beer? If a banana is the only thing on offer at an aid station, then something is wrong. Perhaps a slice of bacon should be offered! (that is just a joke, btw. maybe an avocado or something.) You say that the best athlete is one who’s adaptable. But the circumstances surrounding the athlete’s training are not so much permitting him/her to adapt, as forcing him/her to adapt, to a pre-decided nutritional regimen which is largely hostile to keto and overwhelmingly favorable to carbs, because that’s how it’s been done for decades. It’s not the athlete who refuses to adapt here, it’s the system surrounding what we have come to believe to be good nutrition for human performance, and the poor athlete is given so few options that s/he has no choice but to adapt to the prevailing set-up.
“If eating a banana during a workout or competition will diminish your performance, there’s something wrong with your sports nutrition strategy. That’s not my bias toward sugar talking, ”
Hence, if eating a banana is, in fact, good sports nutrition strategy, that’s only because we have forced it to be so, and it is indeed a bias toward sugar, a bias which is a mirror of the nutritional advice that has dominated the field of human performance and nutrition, and indeed, the field of nutrition for the general population, for some decades.
“To be a successful athlete you have to be able to perform using the fuel available and the equipment you have, in the environment provided.”
Or, in plain English, ‘you’d better be able to extract nutrition from that banana, because that’s all we’re going to give you, and if you can’t get used to that, you have no business being an athlete here’.
Finally, on that same “sauce for the goose” theme,
“Experience also tells me nutritional ketosis will be corrupted by supplement and packaged food industries the same way Atkins, Paleo, Zone, and other have been….. The strategy works, people feel great and lose weight….. The packaged foods and supplements contribute to increased caloric intake, people regain weight, and once the positive results have disappeared their compliance diminishes and they return to their normal food choices and eating behaviors. As soon as you see “keto-cookies”, it’s over.”
Sounds like any diet or nutritional lifestyle, really. And the cookies don’t even need to be keto. As a former athlete myself, I know that cookies are cookies. As soon as you see any cookies at all, it’s over 🙂
Appreciate the time you took to write the article and it’s clear that you are coming from a place where you want the best for your athletes. Keep up the science, it’s worth continuing to learn new things!
just curious if you’ve ever done iron distance triathlons / ultra marathons while on keto ? it seems you’re very much pro keto (or at least very much against someone speaking against it in relation to long distance endurance races). curious if you yourself have raced endurance while purely keto ?
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Would like to see a similar analysis on intermittent fasting options and effect on performance.
Me too. Not only effect on performance in general, but when and how to do it – and how to work IF around competitions, etc.
i would also.
Me too. I know I need carbs but wonder if IF can somehow fit in for some weight loss for a shorter time frame.
I disagree with you on this I have been running for 4 months after an 18 year break from back when I was airborne in the army. I am 43 and after 4 months back on the track I can run a 5k in the 29s and run 5 miles at a 10:40 pace and I have been on a low carb diet for about 4 months. I had 6 carbs the other day and did a 5k in 71 degree weather in 29:42 my personal best so far.
How do you know with certainty that your performance would not improve with the addition of more carbs? Likewise, how do I know that mine would not improve with less? I personally, as an endurance athlete, have no desire to try the keto diet, but the science behind this article is interesting. Great article.
i think the point of the article is geared more towards longer distances and endurance athletes. i’m not sure you could really compare eating strategies for a 5K (you essentially don’t have to eat anything before this race for “fuel”) vs. that of Iron distance, or ultra marathons
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The Ketone Esters that you talk about in your article, our company just launched the World’s 1st Ketone Ester for the public. KetoneAid
Interesting read, I’ve started looking into lchf recently after commiting to a 100mile foot race, my first over the distance, and first ultra for 2 years. I need to shift about 2 stone but the main draw was the reduced reliance on having to eat carbs, as it becomes a real chore over the 24-30hours I expect to be going. After a week of 25-50g carbs i feel good, and have lost the 7lbs of mainly carb-held water. Training has defo suffered as last week easily managed 13miles and this week struggled for 6.5. I understand that there is a difference between ketosis and fat adapted (I believe it can take a month or so).. SO all these articles are excellent in deciding whether it will my work for my very specific goal, or whether I need to up my carbs, or just abandon the experiment due to time constraints.
curious about your experiment. so you initially feel good training low carb (25-50g), then the next week performance suffers ? trying to understand better.
I’m a retired physician. About 20 years ago I utilized the Atkins Diet to take off about 35 pounds that I really didn’t need. What I read in Dr. Atkins’ book and experienced myself was that there is first a rapid loss of 5-7 pounds–mostly water weight–as the ketosis has a diuretic effect. After that, the rate of weight loss slowed a bit.
The single greatest help of the ketosis during the rapid weight loss is that the the ketones are appetite suppressants, so being in ketosis helps one not feel as hungry while one is not treating food, which in turn helps a lot in compliance with the diet. However, what actually happens is that it’s really just basic math–consume fewer calories than you burn, and you’ll lose weight. There is no substitute and no other way. When you stop eating one of the major food groups, your caloric consumption falls, thus the math shows the weight comes off. It’s still 3500 calories per pound of fat regardless of what fad diet one follows. This is true whether it’s Atkins, South Beach, Cabbage Soup, Paleo, or whatever moniker you attach to the diet.
In the end, the ultimate weakness is that any diet that eliminates a major food group is not maintainable long-term for virtually anyone without tremendous self-discipline. This is true whether that food group is carbohydrates or fat or protein. Thus, at some point, the person will stop this “diet”, and will either resume the old dietary patterns (and regain the weight), or will have to change to a new lifestyle of eating to maintain the weight loss.
The other issue is that it’s impossible to exercise enough to overcome poor dietary choices. (Jim Rutledge points this out quite well in another response.) This is all the harder when we’re bombarded with slick marketing of too-readily available energy-dense processsed foods and snacks–especially the tasty ones!
Regardless, there’s no escaping the simple mathematics of the calorie balance. I totally agree with the statement to exercise for fitness and eat for weight management.
You make some great points. The carbs that those in ketosis try to avoid or limit are the breads, pastas and anything that is white or can be white. The body is not a closed system. 1000cals of salmon vs 1000cals of cheese cake will effect the bodies systems differently. While I agree that those in dietary ketosis tend to consume few calories and thus it can lead to weight loss. It is not always the case. Dr. Peter Attia showed this in his personal journey of being in dietary ketosis. Chris Froome and Team Sky have been experimenting with ketosis and exogenous ketones now for 3+ years. The majority of their riding does not require rocket fuel. Fat has become their friend. When necessary they will consume sugar/gels and as they are already fat adaptive and insulin sensitive the sugar acts as the rocket fuel and surprisingly, the effects lasts much longer that the average pro rider, at least that’s what their testing showed. Froome will binge on carbs after a particular hard stage and will consume up to 200grams of carbs. This sugar will go right back to the muscles so he can fight another day.
how did they became fat adapted and also concurrently still tolerate of carb loads ? trying to learn more on the subject.
Hi, as a coach with 5 Spartathlon victories and also course record from this 246Km long running event, I can tell my runners diet is high in carbs. Of course most of the runs are with empty stomach, and some of the long ones with no or minimal carb intake to increase fat burning ability, but specially after training, we are eating carbs.
So periodize training and carb intake as well.
I am interested in the possible inclusion and benefit of exogenous ketone fluids as an additional fuel source for my endurance running training and racing. I have previously made the decision that i neither have the need or the desire to achieve full ketosis for the reasons well articulated in the above CTS article. So, two questions:
1. recommended guidelines/protocols for the inclusion of exogenous ketone fluids?
2. recommended producers/sellers of ketone fluids? Please disclose conflicts/affiliations if you are a producer/seller. THX
A couple years ago I started doing a variation on the “Train Low” idea. On training rides, I also train my metabolism simply by riding as long as is comfortable without eating. My time limit has gradually increased until I can now do a 3 hour hard ride with no food and no discomfort. I do the same when I day hike or snowshoe.
What changes is increased fat use and decreased glycogen use. This is about the same result claimed by the LC advocates. However I eat a HC diet which is also rich in protein. On “serious” or event rides when I want a good result, I eat my usual HC foods right from the start. Actually, I drink a 7:1 maltodextrin/flavored whey protein homebrew and eat little solid food on event rides, brevets, etc. I find I need less of this beverage now than I did before I became “fat-adapted.”
After every ride or workout, I have the usual recommended ~4:1 carb/protein recovery drink.
This adaptive process has not hurt my anaerobic power or anaerobic endurance.
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http://andreobradovic.com/happy-ending/ sorry but I disagree. I am a coach and currently have several clients that were carb a holics like I was. They were also FAT. They are now slim lean and much faster and have less health problems. I have also moved from 25 in my AG to 13th in the country all from being lean and racing on strategic carbs but training largely on a LCHF approach. In the end you can’t say it does not work. If athletes are insulin Resistant and they are FAT then it will help them easily lose excess weight once they adapt they will be healthier and because they have lost excess kgs they will have better pwr to weight ratios and be faster. If people can tolerate a heavy carb approach then great good on them. There is no one size fits all. So maybe go and ask a few people like Dave Scott and other people how they eat… LCHF
To summarize, you eliminated a food group and ate primarily whole foods and lost 22 pounds while continuing to train. Of course you got faster. You used diet to lose weight, but when you want to be competitive you still recognize the benefit of carbohydrate for high intensity. I think you agree with the article more than you disagree with it. – Jim Rutberg, CTS
I transitioned into a keto diet November 2015 while drinking exogenous ketones and it has been very easy to stay with it all Year! I initially started Drinking ketones (and gaining ketosis in less than an hour) because I wanted to get rid of the extra winter weight that comes from not riding much during the off-season. When I dropped all of my gained weight in just a matter of weeks back in December 2015, I started realizing that there were also performance benefits from tapping into my own body fat for fuel!
All last year I fueled my rides that ranged from 40-115 miles (completed 10+ centuries Last year) completely on body fat and Ketones! Absolutely no carbs! My energy during rides is high and consistent with no “bonk”!! On longer rides (80-100mi) I put Ketones in my water bottle and I don’t even get hungry! I also find that I can maintain a higher level of exertion for a longer period of time with little fatigue (because fat fueling requires less oxygen). I notice that during these harder efforts I can maintain a higher heart rate for longer which translates to better performance!! I also notice I recover faster during my rides between hard efforts as well as between workouts! It’s amazing! And I’ve seen the same thing on every ride since starting to use this! Keto diet AND exogenous ketones is AMAZING! It took several months to get used to fueling only on body fat but because I was drinking ketones, my performance never suffered and it only improved after fat-adaption happened!
It sounds like this article was written by someone with no personal experience with fat adaption and using ketones and fat for fuel! I would love to hear you interview Chris Froome and Romain Bardet who are both keto experts!
Regards! Love your other training tips!
exactly totally agree
I’m sorry to say that your comment seems heavily misinformed.
You say that you ‘ wanted to get rid of the extra winter weight that comes from not riding much during the off-season’. Presumably the fact that you actually started training more helped you lose the additional body fat?
You also say ‘I can maintain a higher level of exertion for a longer period of time with little fatigue (because fat fueling requires less oxygen)’. This is simply incorrect as fat actually requires more oxygen to breakdown than carbohydrate. There are multiple studies demonstrating that VO2 is higher as fat utilisation increases.
Finally, your proposal at the end that cyclists such as Chris Froome are keto experts is again simply untrue. I attended a lecture by James Morton (head of performance for team Sky) less than two weeks ago who confirmed that all members of the team follow a periodised carbohydrate rich diet.
We talked about this on FB. I respect the fact you sell Pruvit ketone supplements and you use and believe in the products you sell, but you should include that in your comments. And like Ryan, I have a little trouble with the science behind your statements.
“I notice that during these harder efforts I can maintain a higher heart rate for longer which translates to better performance!!”: How? Heart rate response is affected by hydration status, core temperature, stimulants, fatigue, stress, etc. If anything, producing more power at the same or lower heart rate would be an indication of improved performance. Maintaining a high heart rate for longer doesn’t mean your power output remained high as well, it just means your cardiovascular system was working harder.
I’m glad your performance has improved, but if you lost weight, increased training volume, maybe included some structure, and have been enjoying riding because you feel better, of course your performance (power-to-weight, VO2 max in ml/kg/min) improved. And because of the weight loss you are also better at dissipating heat and have a lower oxygen cost for locomotion, meaning you can go further on less fuel than you consumed before. The exogenous ketones may be helping, but my point is you may be giving the elimination of carbohydrate too much credit for your performance. – Jim Rutberg, CTS
Your comments and they way you CAPITALISE everything make you sound like an infomercial for ketone supplements. Disclosure!
GI has always been my issue. As a hobby nutritionist and scientist I have tried every strategy, being a millimeter man I have worked on percentages amounts per hour bodyweight fluid loss etc. etc. Going LFHC was the single best thing I did to prepare for event over 3 hours. Like so many others I can race and compete all day with maybe 200 calories for an entire 4 hour ride. No doubt, you’re high and will suffer initially until you adapt but then he recovers fine. My power output, heart rate etc. all showed improvement on LFHC. Everyone is different and my gut was always my achilles heal despite tedious attention to detail. No more. I am 56 year old mtn and road rider. My performance and results mostly improved on LFHC but more importantly I felt great and recovered well after events. Once you are keto adapted, you can add carbs back into your fueling for races and events by the way.
Everyone is different metabolically. Laziness with canned workouts and “eat this way” theory are insane at best. Being a type 1 diabetic and listening to the so called experts on what’s best for me always left me struggling to improve. Once I took a step back and looked at my situation, I realized that the LCHF diet was not only a performance enhancer for me but I was able to get off an insulin pump and improve my metabolic function. Now I have been very good at keeping records, to include AIC, Blood pressure, Lactate levels and all I see now Is a slow, consistent improvement. I sleep better, I recover faster, cognitive function has increased, I’m not always wondering have I eaten enough to perform a workout, will I get low while training. All these were of great concern when I showed up at a race with a bar of this, a bar of that, loaded up in my jersey pockets, and whatever was the “craze” for quick energy drink in my bottles. Now I only carry water and just in case flask of energy gel. I can now ride for 3 hours solo, no carbs. I’m 188 lbs, and I’m climbing faster now at endurance then anything I was doing before. I have actually put on weight, what gives? Heart rate overall is lower for any exertion. All I can see now is continually improvement on the horizon. Full disclosure I’m on a 80/15/5 LCHF. Started 12 may 2016. And yes you will see a definite drop off in power and energy level in the first month but I can tell you if your are patient and you figure out “how” much carbohydrates you can tolerate then I believe you are well on your way to make consistent improvements both in health and performance. There is definitely a place for carbohydrate’s in cycling like a crit (1 hr). But lets look at American sports that promote carb’s. How long do they last. Football 1 hour, 4 quarters, 15 min each, Hockey 1 hour, 3 periods, 20 minutes each, Basketball 1 hour, 4 quarters. You ever watch a overtime game, everyone is in slow motion, I thought these were the most highly trained specimen’s in our midst? And how much glycogen stores does “everyone” have? You guessed it enough for 1 hour +/-. So that’s how you are trained into believing a one hour turbo session requires carbs, before during and after. All the best in the new year!!
I’m not type 1 diabetic but i’m on a LCHF “rehab” about a year – not as low as yours, with a 20hs intermitent fasting 2 times per week. I swim, cycling and do resistance training 4/5 times per week and I can say undoubtly that all the results you described happens with me too.
It’s amazing become a non “carb-addicted” and experiences all its benefits – an overall improvement in life and sport performance.
When a I read the article below – an iroman legend sharing his LCHF nutrition daily strategy, it was amazing!!! It gave me strengh to keep punching (going) and stay on focus.
We definitly need much less CHO we think we need.
As an avid reader of Dr Attia and Phinney and Volek I experimented with essentially no carbs for about two months.
From a performance standpoint my ability to do long endurance rides at the top of my endurance zone showed a marked improvement. I could power along for hours with little need for food and much lower water intake, but my top end power definitely suffered. Sprinting and out of the saddle climbing suffered.
Physically I dropped weight even though I was already thin.
Mentally the diet is hard to stay on for more than a few months.
It did force me to rethink everything I eat from a sugar standpoint. I eat far less now.
Same here re riding bikes, I can power along for 200+km without the need to re-fuel, if I choose to.
Mentally, I find this Way Of Eating very easy and straightforward.
I’ve been Low Carb (sometimes Keto, but I hardly every check) for almost 4 years now. So not hard at all!
Also doing Time Restricted Eating every day too. Never any breakfast, 1st meal-time of the day varies according to how I feel. Very occasionally do an extended fast over a day or two or three, but not often at all. Once or twice a year?
Main thing it’s trivially easy to stay super-lean. Which is great (I’m 62).
If only I could be as relaxed about alcohol consumption !! My next ‘challenge’.
We at First Endurance came to these exact same conclusions as Chris in this article. Remembering that we are talking about the benefits to performance in endurance athletes, not the ‘potential’ health benefits to the general public. For endurance athletes the vast majority will seen no benefit from a keto diet. Ultra long distance athletes ‘may’ find that they can perform at an aerobic pace with fewer calories, however if they need to push above threshold levels they will suffer. We feel this benefit may be best reserved for athletes going 20+ hours.
We do feel that spending a few months on a modified Keto diet may benefit the long distance athlete by creating even a slight shift towards using fat as a fuel. Benefits are likely minimal and may only be worthwhile for athletes that have trouble consuming enough calories during long distance exercise. Ultimately glucose/glycogen will be the prefered fuel source when racing and athletes should be prepared by consuming the right sugars at the right times.
Also, keep in mind (didn’t see it mentioned in the article above), that keto diets improve fat utilization *at the cost* of carbohydrate utilization. We can adjust our metabolic profile easily through nutrition, but we need to understand the underlying mechanisms at work. The reason you can’t go hard on a keto diet is not only because of impaired CHO storage, but also because you cannot *access* the CHO due to the PFK reaction in glycolysis being inhibited through high fat oxidation.
I think you are right about performance athletes especially in the younger age groups not having much benefit from strict ketosis. As you age though, the vascular system decline and adipose accumulation that comes with constantly consuming elevated simple carbs will outweigh the desire to be the first to the finish line. There is a sweet spot time period in life for exogenous carbohydrate consumption and that is mostly in our competitive youth. Just my personal experience says that in mid-life, the combined calming effects an empty gut, a state of ketosis, and a mostly aerobic endurance effort are both healthier and more fun than the carbohydrate-centric behaviors that are used in short duration competitions.
I agree with Chris BeHanna’s comment above. LC in the range of 150-200 grams is adequate to fuel most workouts and shift away from the fumes of a high CHO diet. Keto is the extreme low end that has drawbacks that get confused with LC.
One major topic that you did not address was the contribution of a high-carbohydrate diet to heart disease via high levels of insulin. As Jim Fixx unfortunately demonstrated (and as I personally experienced by failing a stress test a few years ago and winning a trip to the cath lab), endurance exercise does NOT offer adequate protection when you are shoveling the wrong things into your mouth.
I’ve adopted a hybrid approach: no grain, very little sugar, and almost never eating starchy vegetables (corn, potatoes, etc.). On an average day, I eat about 100-150 grams of carbohydrate. My lipid profile has become astonishingly good, and my LDL-P (particle concentration, a much better predictor of coronary events than LDL-C), is now just over the lowest-risk threshold. My power at threshold is up dramatically, and I can complete fast, long rides without having to eat along the way (most recently, I finished the Hotter Than Hell Hundred in 4h 47m).
Dr. Peter Attia, himself a triathlete, discusses this at length in his “The Truth about Cholesterol” series on his website, complete with citations to the literature.
What is not realised by a great many people about Jim Fixx is that he was never an endurance athlete of note, but prior to his ‘Road to Damascus’ conversion to distance running, and becoming a much-quoted ‘expert’ with his book, he was a workaholic journalist who smoked several packets of cigarettes a day. Apparently, prior to his death, he never got tested for familial hypercholesterolaemia, (his father died of a heart attack at about age 43); thinking that all his aerobic running was cardio-protective. I think I read that he followed a high-carbohydrate diet, which could’ve messed up his insulin levels and elevated his triglycerides. Due to all the arterial damage from years of smoking, and what seemed to be a compulsive exercise trait, it seems that Fixx died much younger than he should have, however, when considering the very young age of his father at time of death, Jim Fixx may have already suffered extensive cardiac pathology, but may have extended his life with the extensive capillarisation of the heart that aerobic endurance running promotes.Because of his previous smoking history and compulsive endurance exercise habits and possible extended intake of carbohydrate foods, he cannot seriously be cited as the poster boy for the harmful effects of distance running, although now and again his name annoyingly pops up. On the other hand, I know of several accomplished distance runners (one an Olympian and former winner of the New York City marathon) who have developed moderate to severe atrial fibrillation in their 60s, requiring surgical ablation at the A/V node.