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
www.nal.usda.gov/fnic/etext/000054.html
Sportscience, an interdisciplinary site for research on human physical
performance
www.sportsci.org
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