An active lifestyle requires energy. The body uses up energy by keeping muscles moving, temperature stable and organs functioning. The body replenishes this lost energy by digesting food. The more energy is used by physical activity, the more food is needed. As a result, athletes may need to eat more than people living a more sedentary lifestyle.
Basal Metabolic Rate
The body uses up calories by carrying out wide variety of functions. The amount of energy used up in basic functions such as maintaining temperature and working the heart and other organs is called the basal metabolic rate (BMR). A number of formulas exist for calculating BMR, but as a rough guideline, it is approximately equal to the individual's weight in kilograms per hour. An 80 kg male therefore expends roughly 80 calories every hour, for a total of approximately 1920 calories per day. Females spend slightly less than males of equal mass; the approximate BMR is .9 times the weight in kilograms per hour.
Other Activities
The BMR describes the minimum amount of energy required for the body to keep functioning. However, all other physical activities also use up energy. Even an individual who lives a very sedentary lifestyle burns calories walking, lifting objects and making other small movements. An individual who engages in daily exercise uses up much more. Using more calories than are taken in is the key to weight loss, but for athletes who want to maintain a stable weight, the number of calories eaten in a day has to roughly match the number used up.
Calculating Calorie Requirements
The number of calories needed in a day for a male athlete are thus equal to his BMR plus the number of calories burned by physical activity. The U.S. Department of Agriculture recommends 3000 calories a day for a physically active male between 18 and 35. For a more precise figure, each activity can be counted. If the 80 kg athlete from the previous example spends an hour running cross-country, he will burn 720 calories, while 30 minutes of running practice will burn another 400. Adding these to his BMR of 1920 gives a total of 3040, excluding common activities like walking or cycling. If he were a boxer, 30 minutes of training with a punching bag would burn 240 calories, while 30 minutes of sparring would burn another 360 and an hour of heavy weight training would burn 480, for a total of 3000 calories including BMR.
Other Nutritional Considerations
While a steady supply of energy is necessary for athletic activity, athletes have other needs as well. Many foods are high in calories but lack any other nutritional value. Sugary snacks and soft drinks are good examples of this type of food. Athletes should eat a balanced diet including proteins and carbohydrates, with fresh fruit and vegetables to provide vitamins and minerals. A moderate amount of fat is also necessary, although saturated fats are best avoided.
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