Carbs & Exercise
Just the Facts
Why we need carbohydrate for exercise
Carbohydrate plays a crucial role in exercise by providing fuel to produce adenosine triphosphate (ATP) for working muscles. Carbohydrate is unique in that it can be stored in muscles and liver as glycogen for an internal source to fuel exercise, and can also be consumed during exercise to be utilized during endurance activities. With limited stores of carbohydrate in the body—about 500 grams in muscle, 80 grams in liver, and 5 grams in the blood—active individuals need a carbohydrate-rich diet for optimal exercise performance.1
Carbohydrates are not only needed for exercise, but also for the brain and central nervous system. Under normal circumstances, glucose is the only fuel the brain uses to produce ATP and, at rest, about 60% of the glucose found in the blood is metabolized by the brain. That is why is crucial to maintain normal blood sugar concentration during rest and during exercise.
Consuming carbohydrate supports high-quality training. Intake of carbohydrate is not a one-size-fits-all approach; the goal is to have enough carbohydrate available to support exercise. That means that active individuals need different amounts of carbohydrate depending on exercise intensity and duration. A person training for a triathlon needs more carbohydrate than a person who walks a couple of miles every day.
Carbohydrate intakes to support exercise
Active individuals need to consume 50-65% of their total daily calorie intake as carbohydrates. The recommended2 carbohydrate intake is to consume:
- 3-5 g/kg/BW/day* or 1.36-2.27 g/lb/BW/day for low intensity or skill-based sports
- 5-7 g/kg/BW/day or 2.27-3.18 g/lb/BW/day for moderate-intensity exercise for approximately 60 min/day
- 6-10 g/kg/BW/day or 2.72-4.54 g/lb/BW/day for high-intensity endurance exercise for 1-3 h/day
8-12 g/kg/BW/day or 3.63-5.45 g/lb/BW/day for extreme commitment and multiple training session > 4-5 h/day (*g/kg/BW/day = grams of carbohydrate per kilogram of bodyweight each day)
Intake should be individualized to meet the demands of the training or competition. Daily carbohydrate intake depends on training and exercise goals and the concept of carbohydrate availability is used to describe having enough carbohydrate when needed, and less when exercise training is reduced. Therefore, the timing of carbohydrate intake throughout the day should be adjusted up or down.
The concept of carbohydrate quality is often used to encourage the consumption of foods that are naturally rich in both carbohydrate and nutrients. Grains (breads, pasta, cereals, rice, etc.), fruits, and vegetables, including potatoes, beans and peas, as well as some dairy products (milk, yogurt, and kefir) provide carbohydrate along with micro-nutrients that are commonly under-consumed in a typical American diet. The Dietary Guidelines for Americans identifies under-consumed or “gap” nutrients as dietary fiber, choline, potassium, magnesium, calcium, and vitamins A, D, E, and C.
Low carbohydrate intake hurts exercise performance
There are some who advocate for a low-carbohydrate diet for exercise, but research shows that it can hurt, not help, performance. Researchers at the Australian Institute of Sport recruited elite race walkers in a real-life race performance setting to study the effects of a ketogenic low carbohydrate, high fat diet versus a diet with high carbohydrate availability. After three weeks of intense training, the ketogenic diet impaired performance and reduced race speed. In contrast the high carbohydrate diet supported performance.3
The bottom line is that for anyone engaged in regular exercise, adequate carbohydrate intake is required to sustain the capacity for exercise and high-intensity activity. When glycogen stores in muscle reach a critically low level, exercise intensity markedly decreases and performance is impaired. When liver glycogen stores are depleted, blood glucose declines, creating a low blood sugar or hypoglycemia that impairs both physical and mental function.
1 Murray B & Rosenbloom C. Fundamentals of glycogen metabolism for coaches and athletes. Nutrition Reviews. 2017; 76:243-259.
2 Thomas DT, Erdman KA & Burke LM Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and American College of Sports Medicine. J Acad Nutr Diet. 2016; 116;501-528.
3 Burke LM, Ross ML, Garvican-Lewis LA, et. Al. Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. J Physiol. 2017;595:2785-2807. https://physoc.onlinelibrary.wiley.com/doi/abs/10.1113/JP273230
Questions & Answers
Why are carbohydrates under-consumed by active adults?
Active adults often do not consume sufficient carbohydrate to replenish muscle and liver glycogen stores. The reasons include misinformation about carbohydrate nutrition and inadequate understanding of basic sports nutrition concepts. Carbohydrate is unique in that it is used to fuel endurance or aerobic exercise and it is the only fuel that can be used without oxygen, or anaerobically, for intense, all-out effort, like sprinting or jumping. Without sufficient carbohydrate, exercise feels harder, skills and concentration decreases, and fatigue sets in more rapidly.
How many carbohydrates should an active person consume?
It depends on the intensity and duration of exercise, but an active person’s diet should contain 50-65% of their total daily calorie intake as carbohydrates. For those involved in activities such as recreational golf, baseball, or softball, 3-5 g/kg/BW/day or 1.36-2.27 g/lb/BW/day is recommended. For those involved in moderate-intensity exercise for an hour each day, more carbohydrate is needed. Aim for 5-7 g/kg/BW/day or 2.27-3.18 g/lb/BW/day.
How many carbohydrates should be eaten before exercise?
If the exercise last longer than 60 minutes, it is best to eat a few hours before exercise to give the body time to digest the meal and deliver the carbohydrate to working muscles. If you can’t eat before exercise, a small carbohydrate-rich snack of 25-30 grams of carbohydrate can help power you through exercise. Examples include a mini-bagel, 2 fig cookie bars, medium apple, 1 cup of oatmeal, 17 mini-pretzels, a toasted English muffin, or a small blueberry muffin.
Are carbohydrates needed during exercise?
If exercise lasts for 1 to 2.5 hours, 30-60 grams of easy to digest carbohydrates (such as a beverage or gel) can be taken to provide an additional source of fuel to supplement glycogen stores.
How many carbohydrates should be eaten after exercise?
If a meal will be eaten with a within hours of exercise, include carbohydrate with the meal. If the exercise event is an all-day or multiple day tournament (such as tennis or soccer matches), consume small carbohydrate-rich snacks in the hours after exercise. A peanut butter and jelly sandwich with a fruit cup will provide ample carbohydrate for speedy refueling.
Is carbohydrate loading needed for exercise?
Carbohydrate loading is a method to supersaturate the muscles with stored carbohydrate, called glycogen. It can be beneficial for events that last greater than 90 minutes, such as running a marathon or cycling race. For most active people, carbohydrate loading is not needed if they eat a carbohydrate-rich diet in the weeks leading up to an exercise event. One downside of carbohydrate loading is that the extra stored glycogen also stores extra water, making some athletes feel heavy or bloated.
Should athletes eat only low glycemic index foods for better performance?
Glycemic index, an indicator of how a food affects blood sugar levels, has not been shown to improve performance across a variety of different types of exercise. However, the glycemic index can be used as a tool to choose carbohydrate foods for specific exercise situations. For example, foods with a high glycemic index (such as sports drinks, some breakfast cereals, and bread) can help maximize muscle glycogen stores more rapidly than low glycemic index foods (such as milk, yogurt, pasta) when there is limited recovery time between workouts. Glycemic index is a tool that can help athletes fine tune their diet, but should not be used exclusively to plan diets for active people.