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What are the nutritional needs of athletes?

"Eat to compete" has become something of a rallying cry among both amateur and professional athletes. Health food stores and sports shops offer a variety of ergogenic (performance-enhancing) vitamin supplements and concoctions of ingredients such as amino acids, bull testicle extracts, ginseng, and bee pollen. Do these products really enhance athletic performance? Nutrition researchers insist they do not.

The same principles of moderation, variety, and balance that characterize good nutrition for the general population also apply to athletes. Contrary to popular belief, vitamins and minerals do not provide energy, but they are necessary in adequate amounts to properly metabolize the body's real sources of energy — carbohydrates, fats, and protein. Still, athletes require more of certain nutrients than their sedentary counterparts.

Why is nutrition important to athletes?

Without an adequate reserve of energy, an athlete simply cannot perform at his or her peak ability. The human body has about 600 groups of muscles, which are made up of millions of tiny elastic fibers. Depending upon the sport, a conditioned athlete may double his or her muscle mass. Working and maintaining this increased muscle mass requires extra calories. The type of exercise determines what sort of energy reserve is needed. Glucose (blood sugar), which is most readily derived from carbohydrates, is the body's major fuel. Fatty acids can also be burned directly, or converted to glucose. Protein is used mostly to repair and maintain muscle tissue, but it also can be converted to glucose to meet energy needs.

Muscle tissue holds small reserves of fatty acids and glycogen (the stored form of glucose), which can be called upon during a workout. All-out physical effort, such as sprinting, quickly exhausts these reserves, and the muscles then must call upon liver stores of glycogen and fatty acids from body fat. Glucose can be burned with oxygen (aerobically) or without oxygen (anaerobically), but fatty acids can be burned only aerobically. During intense exercise, the lungs simply cannot

keep up with the muscles demand for oxygen; hence, stored glycogen and blood glucose are burned.

During less intense, sustained exercise such as long­distance running, the muscles can burn more fat, sparing the body's body's reserve of glycogen. A pound of stored body fat can provide enough energy to run about 35 miles; in contrast, the body's glycogen reserves are exhausted after about 2 hours.

How much nutrition do athletes need?

First and foremost, an athlete needs extra calories to ensure a steady supply of energy. For example, a sedentary person who weighs 140 pounds needs about 1,680 calories (12 calories per pound) each day, compared with 2,560 to 3,600 calories (18 to 20 per pound) for a competitive athlete.

In addition, a competitive athlete may have increased needs for some vitamins and minerals, including:

• Iron, which is needed to make hemoglobin, the pigment in red blood cells that carries oxygen. Some athletes have an increased turnover of red blood cells, and may require extra iron to make hemoglobin. Women athletes are particularly vulnerable to iron-deficiency anemia because they lose blood during menstruation.
• B vitamins, which are needed to convert carbohydrates, proteins, and fats into energy.
• Calcium, which is essential to maintain bones. Lean women athletes (e.g., gymnasts and ballet dancers) may need extra calcium, because they often do not produce enough estrogen to maintain strong bones.
• Fluids and electrolytes (sodium, potassium, and magnesium), which are needed to replace those lost in heavy perspiration.
• Carbohydrates (sugar and starchy foods), which are converted to glucose. Many athletic trainers advocate carbohydrate loading — consumption of high-carbohydrate

meals — for several days before competition. This increases glycogen and is of the greatest benefit before endurance events. It also increases the amount of body water.

What happens if athletes don't get enough nutrition?
An undernourished athlete lacks the needed energy reserves. Some sports, such as diving, gymnastics, and ice skating, require that participants be excessively lean. Too little body fat can result in serious metabolic disturbances. Women who lose too much body fat often cease to menstruate; young girls who are too thin may have delayed puberty and poor growth.

What happens if athletes get too much nutrition?
Like anyone else, athletes who consume more calories than are burned gain weight. Athletes require some body fat, but too much fat reduces their ability to perform.

Should athletes take supplements?
In general, adequate nutrition can be obtained from a balanced diet. Some supplements promoted to athletes are potentially harmful, especially amino acids, high-dose B vitamins, and iron.

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