Can a marathoner, cross-country skier, weight lifter, or competitive swimmer eat to win? A diet of 60% or more carbohydrate, 18% protein, and 22% fat should be adequate to support frequent, strenuous activity.

Macronutrients

As the source of immediate energy, carbohydrates are the athlete's best friend. Athletes should get the bulk of their carbohydrates from vegetables and grains in frequent meals, because the muscles can store only 1,800 calories worth of glycogen.

Many people erroneously believe that an athlete needs protein supplements. Excess dietary protein, however, can strain the kidneys in ridding the body of the excess nitrogen, dehydrating the athlete as more water is used in urine. The American Dietetic Association suggests that athletes eat 1 gram of protein per kilogram of weight per day, compared to 0.8 grams for nonathletes. Athletes should not rely solely on meat for protein, because these foods can be high in fat. Supplements are only necessary for young athletes at the start of training, under a doctor's supervision. Too little protein in an athlete is linked to sports anemia, in which hemoglobin levels decline and blood may appear in the urine.

The body stores 140,000 calories of fat, so it is clear why no one needs to replenish that constantly with fatty foods. Athletes should use low-fat milk and meats.

Water

A sedentary person loses a quart of water a day as sweat; an athlete may lose 2 to 4 quarts of water an hour! To stay hydrated, athletes should drink 3 cups of cold water 2 hours before an event, then 2 more cups 15 minutes before the event, and small amounts every 15 minutes during the event. They should drink afterward too. Another way to determine water needs is to weigh in before and after training. For each pound lost, athletes should drink a pint of water. They should also avoid sugary fluids, which slow water's trip through the digestive system, and alcohol, which increases fluid loss.

Vitamins and Minerals

If an athlete eats an adequate, balanced diet, vitamin supplements are not needed. Supplements of sodium and potassium are usually not needed either, because the active body naturally conserves these nutrients. To be certain of enough sodium, athletes may want to salt their food; to get enough potassium, they can eat bananas, dates, apricots, oranges, or raisins.

A healthy pregame meal should be eaten 2 to 5 hours before the game, provide 500 to 1,500 kilocalories, include 4 or 5 cups of fluid, and be high in carbohydrates, which taste good, provide energy, and are easy to digest.