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Carbohydrate-Loading Diet

Carbohydrates are the most efficient fuel for energy production. They can also be stored as glycogen in muscles and the liver, functioning as a readily available energy source for prolonged, strenuous exercise. For these reasons, carbohydrates may be the most important nutrient for sports performance. Emphasizing grains, starchy vegetables, fruits, low-fat dairy products, and carbohydrate-replacement beverages, along with reducing intake of fatty foods, results in a relatively high-carbohydrate diet.

Why do people follow this diet?

A carbohydrate loading diet (also known as carbo-loading) is a strategy used by endurance athletes to increase muscle glycogen reserves in order to improve performance. Glycogen is the body’s storage form of glucose, the chief energy source for the body. When carbohydrates are consumed, the body changes much of them into glucose. Glucose that is not needed immediately is stored as glycogen in the muscles for later use. Normal levels of muscle glycogen are more than enough to maintain exercise lasting less than 75 minutes. However, intensive training in endurance sports lasting longer than an hour depletes muscle glycogen stores, increasing the need for carbohydrate intake to assure normal levels of blood glucose and sufficient muscle glycogen reserves.

What do the advocates say?

Research has found that carbohydrate loading diets improve endurance athletes’ performance. Carbohydrate loading can be accomplished in two stages: the depletion stage and the carbohydrate loading stage. On day one of the depletion stage, the athlete trains to exhaustion in his or her sport in order to deplete muscle glycogen in specific muscles. The athlete must engage in the sport during this stage because carbohydrate loading only occurs in the specific muscles exercised. For the next three days, a high-fat, low-carbohydrate diet (60–120 grams carbohydrate) is consumed while the athlete trains moderately. During the carbohydrate loading stage, the diet is switched to a high-carbohydrate intake (400–600 grams carbohydrate) for the next three days, while training time is reduced. This will result in muscle glycogen “packing,” increasing the muscle glycogen to a new, higher level.

Following a less stringent, modified carbohydrate loading diet can eliminate potential problems with the classic carbohydrate loading diet. The modified carbohydrate loading plan is followed for six days prior to competition. It requires the athlete to consume a 50% carbohydrate diet for the first three days and then increase to a 70% carbohydrate diet (or 4.5 grams per pound of body weight) for the last three days before competition. The athlete begins training at a high aerobic intensity; then training time is gradually reduced on successive days.

What do the critics say?

Some problems associated with the classic carbohydrate-loading diet include increased blood cholesterol and urea nitrogen levels, which may cause problems for people susceptible to heart disease, diabetes, or kidney disease. The glycogen depletion stage may cause vitamin and mineral depletion, ketosis, the loss of lean tissue, and a reduction in training capability leading to a negative effect on performance.

Are there any groups or books associated with this diet?

Nancy Clark’s Sports Nutrition Guidebook by Nancy Clark, RD. Campaign, IL: Human Kinetics, 1997.

USDA Food and Nutrition Information Center, Fitness, Sports and Sports Nutrition, Associations/Organizations
http://www.nal.usda.gov/fnic/etext/000054.html

Sportscience, an interdisciplinary site for research on human physical performance
http://www.sportsci.org

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