People have strong feelings about carbohydrate, despite the fact it is neither good nor bad. The positive and negative effects of carbohydrate on health, performance, and recovery come from when, why, and how much people consume. For endurance athletes, carbs are an essential fuel for performance and recovery. To understand this critical component of sports nutrition, here’s a guide to optimizing carbohydrate intake before, during, and after training – and in your everyday diet.
What are Carbohydrates?
Along with fat and protein, carbohydrate is one of the three macronutrients humans rely on for energy intake. Monosaccharides are the basic building blocks that create everything from the simplest sugars to the most complex carbohydrates. The three monosaccharides are glucose, fructose, and galactose. These can be combined to form disaccharides maltose (2x glucose), sucrose (fructose + glucose), and lactose (glucose + galactose). All forms of sugar are eventually broken down to glucose before being oxidized in mitochondria to liberate energy for working muscles. Glycogen, the storage form of carbohydrate found in muscles and the liver, is a polymerized chain of glucose.
Carbs in an endurance athlete’s daily diet
There is no perfect macronutrient composition that works for every athlete at all times of the year. The amount and percentage of energy intake from carbohydrate changes throughout the year, based on the volume and intensity of training. As a starting point, endurance athletes should aim to consume about 50% of total daily caloric from carbohydrate. From there, carb intake should increase up to 10% as training volume and/or intensity increases, or decrease by about 10% as training volume and/or intensity decrease.
Fruits, vegetables, and grains make up the primary sources of carbohydrate. Ideally, athletes should consume carbs from whole foods rather than highly processed ones. Fresh fruits and vegetables are nutrient dense, in that they deliver substantial amounts of vitamins, minerals, fiber, and water with their carbohydrate energy.
Concentrated carbohydrate sources are more calorically dense, meaning they deliver a lot of carbohydrate energy in a relatively small volume of food. Bread, pasta, rice, and potatoes are examples of concentrated carbohydrate foods. Both nutrient dense and calorically dense carb sources have a place in an athlete’s diet.
How athletes use carbs
Humans burn all three macronutrients for energy; the amounts and percentages of each vary based on energy demands. The vast majority of energy for muscular work comes from breaking down fat and carbohydrate. At rest and during activities of daily living, almost all energy is supplied through aerobic metabolism of fat.
As the rate of energy demand increases, the percentage of carbohydrate in the fuel mix increases. The “Crossover Concept” describes the inverse relationship between fat and carb utilization with increased exercise intensity. Moving the crossover point to the right means you can sustain a higher exercise intensity at a 50/50% mix of fat and carbs.
Most energy for high intensity efforts comes from anaerobic glycolysis, which exclusively breaks down carbohydrate for energy. At maximum intensity the contribution from carbohydrate approaches 100%. As a result, we often consider carbohydrate as an endurance athlete’s high-performance fuel. Race-winning efforts are fueled by carbohydrate, as is the training that creates race-winning fitness.
Pre-Ride Carbohydrate Intake
To execute high-quality workouts, cyclists benefit from starting with full glycogen stores and normal blood glucose levels. In other words, you want carbohydrate on board. This is particularly important before moderate-intensity endurance rides, moderate/hard group rides, and high intensity interval workouts and races.
Starting a workout with full glycogen stores depends on your daily nutrition strategy, as muscle glycogen replenishment can take 24 hours. Your pre-ride carbohydrate intake aims to top off glycogen stores and/or boost blood glucose levels.
To eat enough for a great workout, but not so much that you suffer gastric distress, remember this formula: 1 gram of carbohydrate per kilogram of bodyweight for each hour before training/racing, up to a maximum of 4 hours or 4 g/kg. In other words, 4 g/kg four hours out, reducing to 1 g/kg an hour or less before the start.
Along with reducing the g/kg of carbohydrate in a pre-ride meal or snack as your workout approaches, you should also reduce the complexity of the carbohydrates consumed. Complex carbohydrates and meals that contain substantial amounts of fat, protein, and fiber work when you have 2-4 hours for digestion. As the workout approaches, prioritize simpler carbohydrates. Pre-ride snacks within 60 minutes of training should be almost entirely carbohydrate.
Carbohydrate intake during rides
Consuming carbohydrate during rides improves power output, delays glycogen depletion, and provides fuel for high intensity efforts late in the ride. Rides shorter than about 75 minutes can be entirely fueled by glycogen stores. However, some research indicates oral carbohydrate rinses can improve performance during short, high intensity workouts. For rides longer than 75 minutes, athletes should start consuming carbohydrate in the first 15-20 minutes and continue through the end of the session.
The amount of carbohydrate cyclists should consume per hour depends on exercise intensity. The standard sports nutrition recommendation of 30-60 grams of carbohydrate per hour of aerobic exercise is based on the fact most people can only absorb about 1 gram of carbohydrate per minute.
Through training and by consuming a mixture of sugars, athletes can increase absorption to 90 grams of carbohydrate per hour. Recent research suggests this could even extend to 120 g/hr.
However, just because you can eat more doesn’t mean you need to. Most cyclists perform best by consuming carbohydrate calories equal to about 20-30% of their hourly energy expenditure. In other words, at a moderate endurance intensity of 600 Calories per hour, aim to consume 120-180 food Calories of carbohydrate per hour. Carbs contain 4 Calories per gram, so 120-180 Calories equals 30-45 grams of carbohydrate.
Carbohydrate intake after rides
Post-ride carbohydrate intake aids recovery by accelerating muscle glycogen replenishment. Maximizing the rate of glycogen replenishment is most important when the rest interval between training sessions or competitions is shorter than 24 hours. When this is the case, athletes benefit from recovery drinks that are carbohydrate-rich and contain some protein. The exact percentage of carb:protein in recovery drinks is less crucial than having “mostly carb, less protein”.
Proactive glycogen replenishment strategies are less necessary when athletes have at least 24 hours of recovery time. That doesn’t mean the 60-minute post-workout “glycogen window” is useless. (Update on “nutrient timing” and the glycogen window.) The glycogen window is an opportunity to maximize glycogen replenishment. But if you miss the window, it’s not a disaster. You can fully replenish muscle and liver glycogen from your daily diet within 24 hours.
For most time-crunched cyclists who train 3-5 times a week for a total of 6-10 hours per week, the best post-workout carbohydrate advice is: eat a normal-sized, balanced meal containing carbs, fat, and protein within 60 minutes after your training session. After particularly long or strenuous rides, consider a carbohydrate-rich recovery drink immediately, followed by the aforementioned meal within about an hour.
What about post-workout protein? Read this.
Additional Carb Considerations
In addition to the general recommendations for carbohydrate intake before, during, and after cycling, here are some more advanced considerations.
Carbohydrate Availability Training
Athletes and coaches sometimes manipulate carbohydrate availability to target substrate utilization during training. Common methods to train with low carbohydrate availability include “Train Low” and “Sleep High, Train Low”. The goal is to start rides with mostly depleted glycogen stores to prioritize fat oxidation. You can read more about Train Low methods for cycling here.
At the opposite end of the spectrum, athletes should prioritize high carbohydrate availability prior to interval workouts. This includes moderate-intensity aerobic intervals like Tempo and Sweetspot Tempo, and high-intensity intervals above lactate threshold. Carbohydrate matters for these workouts because success depends on achieving and sustaining target power outputs.
Bonking is an endurance training term that refers to a profound depletion of glycogen from exercise. It results in loss of power, nausea, disorientation, and loss of coordination. Eventually, it leads to an inability to continue exercising. Bonking is different than exhaustion. It’s not a matter of overexertion, but rather undernourishment.
Fortunately, athletes can rapidly reverse the effects of bonking by consuming a relatively small amount of carbohydrate. The response time to carbohydrate ingestion can be as short as 10 minutes. Although athletes may start feeling a little better quickly, full recovery of performance capacity may take 30 minutes or more.
Because the response time to carb ingestion is so rapid, athletes can prevent bonking if they recognize the symptoms. Signs of glycogen depletion leading to bonking include feeling hungry or “empty”, reduced ability to focus, lightheadedness, and a sudden reduction in sustainable power output.
Ketogenic and Low Carb Diets for Endurance Athletes
In the general population, low carbohydrate diets gained popularity for promoting weight loss, improving insulin sensitivity, and a host of real and imagined health benefits. A deep dive into low carb diets is beyond the scope of this article, but we mention them here because we don’t recommend extremely low carb lifestyles – including ketogenic diets – for endurance athletes.
Some athletes can achieve weight loss and/or improve athletic performance through training gains while following a ketogenic or low carb nutrition strategy. However, that’s largely because they started with significant room for improvement. Even suboptimal training or moderate caloric restriction would have resulted in similar improvements.
For most athletes – even elite athletes – long-term ketogenic and low carb lifestyles result in lost opportunities to maximize athletic performance. For more on this topic, read this on ketogenic diets and this on fat-adapted athletes. Although the latter is directed at ultrarunners, the concept applies equally to cyclists.