Carbohydrates and Fitness: Helping Athletes Reach Optimal Performance

Even the most talented athletes can't reach their potential without proper nutrition. Whether your client is training for a big event, or just wants to be more active - eating smart every day is important. This carbohydrate fact sheet is a nutritionist's guide to athletes' commonly asked questions about eating for performance.

What diet is best for me?

• Physically-active people should eat a carbohydrate-rich (55-65% of energy), adequate protein (10-15% of energy), and low fat (25-30% of energy) diet - similar to the recommendation for average healthy people. However, athletes generally need more calories to maintain energy levels.
• Carbohydrate-rich foods are often an easy way for athletes to get the extra energy they need. In addition, carbohydrate intake is directly related to the amount of glycogen stored in the muscle. It only takes 2-3 hours of moderate exercise to deplete muscle glycogen stores. To maintain glycogen stores, it's important for athletes to eat a diet high in carbohydrate every day.

Why is carbohydrate important?

• Carbohydrate is a vital source of energy needed for normal brain functioning, maintenance of glycogen stores, and sparing of muscle breakdown for energy. A supply of muscle glycogen is essential, both to prolong aerobic metabolism and to fuel anaerobic metabolism.
• An increase in dietary carbohydrates (600 grams per day) can raise the glycogen content of the muscle by two to three times the normal level. Sports scientists agree that increased glycogen stores in the muscle can increase sports performance by sustaining high-intensity endurance exercise.

What type of carbohydrate is best?

• Both simple and complex carbohydrate are effective in increasing muscle glycogen stores and both are important components of an athlete's diet.
• Perhaps a better indicator, rather than the type of carbohydrate, is the glycemic index which categorizes carbohydrate by the effect the food has on a person's blood glucose.
• Although using the glycemic response of foods can be very helpful, it is important to remember that people greatly vary in their response to different foods and that the glycemic index of mixed meals differs from when the food is eaten alone.

What should I eat before an event?

• A pre-event meal helps to build glycogen stores and prevent hunger before and during the event. Consuming 200-350 grams of carbohydrate three to six hours before endurance exercise can help to improve performance. It is important to note that although some studies show that consumption of any carbohydrate food prior to exercise will cause a transient decrease in blood sugar levels early in exercise (1); this hypoglycemia does not adversely affect the performance of most individuals (2,3,4).
• A combination of both high and low glycemic index foods before an event assists in maintaining blood glucose levels throughout exercise and prolongs endurance (1).

What should I eat during an event?

• Eating carbohydrate during a long-duration event (greater than two hours) of moderate to high intensity helps performance. Depleted glycogen stores can cause fatigue and poor performance. About 30-75 grams of carbohydrate, from foods such as candy or a glucose drink, should be eaten each hour throughout the event to maintain normal blood sugar levels as well as to provide an active source of energy for exercising muscles.
• During an event, high glycemic index foods should elevate blood glucose initially, while moderate and low glycemic index foods should maintain blood glucose throughout the exercise and delay fatigue (5).

What should I eat after an event?

• Eating immediately after exhaustive exercise conserves lean tissue and helps rebuild glycogen stores. 100 grams of carbohydrate consumed immediately after exercise and 100 grams again about one to two hours later are recommended.
• After exercise, carbohydrate foods with a high glycemic index have been shown to promote more rapid glycogen synthesis than lower glycemic index foods (6).