Meeting Energy Needs

Three nutrients supply energy:

Carbohydrates are the body’s first choice for its energy, therefore, it is the nutrient that athletes need the most. Overweight athletes should decrease fat, not carbohydrates, in their diets. Complex carbohydrates (starches) are more useful than simple carbohydrates such as sugars. Sugars are not helpful because they are used more quickly than is useful for performance.

Fats release more than twice the energy of carbohydrates and proteins. However, fat is not the form of energy the body prefers to use. In addition, it is not very effective unless carbohydrates are also present.

Usually, most people don’t start to use fat as fuel for exercise until the workout is 20 minutes or longer. Fat is not used as a primary fuel until after two hours of exercise. For example, during sprinting, carbohydrates supply the necessary fuel, but during endurance events (such as marathon running), the body burns both carbohydrates and fat. The body obtains more of its energy from fat as the endurance activity continues.

Protein is used by the body much more for growth and repair than for energy. It is not a very good energy source.

The Practice of “Carbohydrate Loading”
In endurance events like a marathon, athletes may experience a feeling known as “hitting the wall.” These athletes have run out of stored carbohydrate energy; it feels as if a brick wall is between him or her and the next step. Normally, there is enough stored carbohydrate to last an hour and a half to two hours of continuous exercise. Thus, for stop-and-start games such as basketball and football, or for events lasting an hour or less, the body has no need for an extra fuel; carbohydrate loading is of little value.

To enhance endurance, “carbohydrate loading” is a dietary practice that packs muscles with higher than normal levels stored carbohydrate energy, called “glycogen.” The athlete eats a diet very high in complex carbohydrates, approximately 65 to 70% of total calories, for four to five days before a sustained event that lasts more than two hours, and then exercising only lightly (if at all) until the event. This practice is common, and it has value, for those athletes who compete for several hours at a stretch, such as:

The last meal eaten before a performance won’t create a magical performance. Carbohydrates are digested quickly; a meal heavy in fat will take longer to digest. Digestion takes approximately three to five hours to complete; performance could suffer if the body has to concentrate on digestion instead of muscular activity.

Protein Needs
Protein is needed to build muscle and tissues. A regular, varied diet provides enough protein to meet an athlete’s needs. At least some of this protein should be from animal sources, such as meat, eggs, and dairy products. Note that the average American diet already includes much more protein than the requirement as stated by the Recommended Dietary Allowances (RDA’s). Consider, for example, a single whole chicken breast; it provides 52 grams of protein, almost the entire (or more than) RDA for the average teenager.

The Practice of “Protein Overloading”
Many athletes assume that more protein will make them more muscular. Athletes, as well as coaches, believe that very high-protein intakes, including protein supplements are needed. Unfortunately, this is a misconception. Exercise, not dietary supplements, builds more muscles.

Research studies show that muscle builders develop their physique through exercise and lifting weights and not because of healthy dietary practices. One of the largest abusers of protein overloading are bodybuilders who think to make their muscles bigger they need to consume large quantities of protein from food. Protein sources include meat, eggs, and protein beverages, especially during the month before a competition. This is not only dangerous, but also self-defeating. To provide the energy needed for the regimen of exercise bodybuilders perform, they need carbohydrates not protein. On a low carbohydrate diet, muscle carbohydrate stores (glycogen) become depleted; consequently, bodybuilders experience chronic fatigue.

There are risks to protein overloading. In addition to the disadvantages of a high-fat, high-cholesterol diet, protein overloading may cause:

The Need for Water
An athlete’s need for water greatly exceeds that of non-athletes. Athletes lose a lot of water through perspiration. The energy released during exercise is heat, and this heat must be disposed of to avoid a rapid and dangerous increase in body temperature; the body cools when sweat evaporates.

Non-athletes lose approximately a quart of water daily from sweating. Athletes involved in strenuous exercise may lose two to four quarts (four to eight pounds) per hour. Even a 3% weight loss from sweating (4.5 pounds for a 150-lb person) causes fatigue and decreased performance. A weight loss of water between 5 and 10% of body weight is serious dehydration. Water loss can lead to:

Sometimes vigorous exercise masks the normal thirst signals. For this reason, it is very important for athletes to be sure to consume plenty of liquids. To determine how much water is needed, an athlete should weigh themselves before and after training and monitor their water intake during the training period. For each pound lost, athletes should drink two cups of water.

The best source of fluid is water. Large amounts of sugary drinks should be avoided. These beverages actually decrease the speed at which water leaves the stomach; they do not re-hydrate the body as quickly as water.

Potassium and Sodium Needs
In addition to water, potassium and sodium are lost in sweat during high-intensity exercise. These nutrients are important for:

While athletes who perspire profusely may need more sodium and potassium, they seldom need special supplements or beverages to get it. Many foods contain these nutrients.

Sources of potassium include:

Sources of sodium include:

The Wrong Track
Performance enhancing properties of certain nutrients have been promoted by health magazines and the sports industry, in particular vitamins C and E, and the B complex vitamins. Unfortunately, large doses of vitamin supplements do not improve performance unless a previous nutrient deficiency existed.

“High energy” athletic beverages may be promoted because they contain vitamin E, certain B vitamins, sodium, potassium and magnesium. There is no scientific evidence that an extra supply of vitamin E and certain B vitamins increases endurance or prevents fatigue. The nutrients athletes need can be supplied by the varied diet they eat.

Salt tablets, or sodium in athletic beverages, are promoted to replace the salt lost from the body through sweat. There is rarely enough salt lost in sweat to require additional salt intake with tablets. There are disadvantages to using salt tablets. Too much salt will:

The best way to replace fluids lost through sweat is by drinking water.

There is no scientific basis for the following foods and additives that have been promoted as having performance enhancing properties, such as wheat germ, lecithin, honey, gelatin, phosphates, bee pollen, and kelp.

Caffeine has been suggested as a performance enhancer, but although some studies indicate it may be helpful in endurance events, it triggers increased urine excretion. Too much caffeine contributes to dehydration.

Iron and Women Athletes
Sports anemia is a condition that may occur in some female athletes. It tends to appear during the early stages of training. The cause is not known for certain, but it is suspected that there are several factors influencing the development of the condition, including:

The best way to avoid iron deficiency leading to sports anemia is to eat plenty of foods that are sources of iron. These include:

Eating Disorders in Athletes
While most people consider athletes to be vigorous and healthy, some athletes restrict their diets. There is alarming evidence of young athletes who suffer from eating disorders, such as anorexia nervosa and bulimia. In fact, some athletes may share some of the characteristics of individuals with anorexia nervosa, such as extraordinarily high self-expectations and tolerance of physical discomfort.

The primary factors that influence eating disorders in athletes appears to be an extreme emphasis on leanness which is both self-imposed and encouraged by coaches in such weight-regulated activities as:

Athletes and coaches need to recognize the dangers of pushing the goal of leanness beyond the point where it may harm performance. Eating disorders can have lethal consequences.

Some bizarre and dangerous eating habits can develop. For example, wrestlers striving to qualify for lower weight classes may try to control their weight by:

Even if daily multivitamin and mineral supplements are taken, deficiencies can occur with such bizarre eating behaviors. In addition, such behavior places a strain on the heart, digestive system, liver, and kidneys.

Back to top


© Copyright (2002) Purdue University, West Lafayette, Indiana, 47907. All Rights Reserved.