By Chris Carmichael,
Founder and Head Coach of CTS
The difference between fueling performance with carbohydrate and consuming too much added sugar is one of the more confusing aspects of nutrition for athletes. Too much added sugar in your diet can be harmful to your health, but consuming carbohydrate – including simple sugar – can be beneficial to athletic performance. This leads to a dilemma for some athletes who want to fuel high performance and simultaneously reduce sugar intake. Thankfully, you can accomplish both.
When we talk about consuming carbohydrate, it includes everything from whole fruits and vegetables, whole grains, processed grain, table sugar (sucrose), and monosaccharides like fructose and glucose. But when doctors, dietitians, and government agencies warn about the health risks associated with consuming large amounts of sugar, they are not talking about all carbohydrates. Excess consumption of added sugar, sometimes referred to as “free sugar”, is the problem, and it is associated with increased risk for obesity, insulin resistance, Type II diabetes, cardiovascular disease, and other health problems.
When a food contains ‘added sugar’ it means sugar that was not naturally present in a food or ingredient and was added during preparation or cooking. And in packaged foods it’s everywhere. Nearly 75% of pre-packaged foods and drinks contain added sugar, although finding it can be somewhat difficult because it goes by dozens of names. High-fructose corn syrup is an obvious one, but “cane juice crystals”, “muscovado”, and even “brown rice syrup” sound a lot healthier.
Why added sugar is a problem
The issue isn’t which plant created the sugar, it’s how that sugar has been refined, concentrated, and stripped of the nutrients and fiber that originally accompanied it. Here’s why:
- Increased energy density: adding sugar increases the number of calories in the same volume of food. This makes it very easy to consume more total energy than you think you are.
- Throws off nutrient balance: there is a lot of naturally occurring sugar in fruit, but it also has fiber and micronutrients necessary for utilizing sugar and a variety of other necessary functions. The fiber slows the absorption of sugar and helps you feel full before consuming way too much.
- Can damage your liver: overconsumption of sugar, particularly fructose, contributes to the development of non-alcoholic fatty liver disease. As obesity rates in the United States have increased, so has the prevalence of NAFLD, but lean people can develop it also.
- Leads to insulin resistance: because the absorption of added sugar is fast, blood sugar levels spike quickly, leading to a rapid release of insulin to remove the sugar from your bloodstream. Over time this can lead to insulin resistance, which happens when you have to produce more and more insulin before muscles, fat tissue, and the liver will respond and take in sugar. Over time, insulin resistance contributes to the development of Type II diabetes.
- Messes with hunger hormones: Leptin levels affect perception of hunger. When you have lots of leptin in the bloodstream, you feel less hungry. When leptin levels are low, your brain thinks you are running low on energy and ramps up your appetite. Consuming a lot of added sugar can lead to leptin resistance, whereby high levels of leptin in the blood no longer signal satiety and you either eat more before feeling full or feel hungry sooner after finishing a meal.
Why training with sugar is not a problem
I’ve lost track of how many times I’ve encountered lightheaded, slightly confused cyclists who clearly need to eat and who respond to the offer of a gel or a carbohydrate gummi with, “Oh, I don’t eat sugar.” If you want to minimize the amount of added sugar you consume outside of exercise, that’s great. During prolonged exercise, and to a lesser extent immediately before and after exercise, simple sugar is useful, effective, and doesn’t come with the risks and problems mentioned above.
Many of the aforementioned problems associated with sugar are tied to consuming it at rest. Your body needs to do something with the energy you consume, and when you’re not active enough to burn it, your muscles are already full of glycogen and/or you don’t have much muscle available to store it, blood sugar levels stay elevated longer and more carbohydrate is stored as fat.
During exercise, carbohydrate metabolism is different. As muscle cells use glucose to produce energy, the amount of glucose they transport from the blood into the cell increases, without the need for insulin. As exercise reduces blood glucose levels, insulin secretion decreases and glucagon secretion increases. Glucagon does the opposite of insulin, helping liberate glucose from its storage form (glycogen) in muscle cells and the liver to increase blood glucose levels. The point of that abbreviated physiology lesson is to say that during exercise the sugar you ingest doesn’t lead to a spike in insulin or contribute to liver damage or leptin resistance.
After exercise, when muscle and liver glycogen levels are low (or at least not completely full), you have capacity to quickly store sugar as glycogen, whether that sugar was ingested as table sugar or a banana or a potato. Exercise also increases muscle mass (compared to sedentary individuals) and increases the amount of glycogen you can store in muscles. Importantly, exercise also increases insulin sensitivity, which means less insulin is required to make muscle cells respond and move glucose from the blood into the muscle.
Manipulating carbohydrate availability in training
Although exogenous carbohydrate is effective for improving performance during prolonged exercise that involves hard efforts (like interval workouts and bike races longer than an hour), there are times when training with low carbohydrate availability can be beneficial. You can read more about the “Train Low” concept in this article.
Added Sugar is for Exercise Only
You don’t have to avoid added sugar or simple sugar during exercise, but that doesn’t mean you can or should only consume added sugar or simple sugar while exercising. Complex carbohydrates and foods that contain fiber, fat, and protein are all parts of a sound sports nutrition strategy.
Early on in long endurance events, or when intensity is relatively low, sandwiches, bars, rice balls, and other solid foods are great for providing sustained energy because the carbohydrate is absorbed into the blood stream more slowly, and those foods are more filling to help you from feeling hungry.
During more intense exercise and later in long endurance events, when muscle glycogen is nearly or entirely depleted, carbohydrate gels and chewables, as well as other concentrated sources of simple sugar get into the bloodstream and into muscle cells fast. Better yet, because fructose and glucose utilize different pathways, you can increase the amount of sugar you can process per hour, from 60 grams/hr up to 90 grams/hr, by consuming sports nutrition products that contain both (think more doors, less waiting).
When added sugar doesn’t serve a useful function, which is pretty much anytime more than an hour before or after exercise, you are better off prioritizing whole foods without added sugar.