Optimal nutrition improves physical activity, athletic performance and recovery from exercise, whether one exercises recreationally or trains as a competition athlete. Consuming adequate food and fluid during, before, and after exercise does several things: maintains blood glucose, maximizes performance, and improves recovery time.
Athletes who do not consume enough food to make the energy their bodies need risk nutrient deficiencies, loss of muscle mass and increase risk of injury and illness. In particular, female athletes who undereat put themselves at risk for low bone mass and ammenorhea. Athletes who desire weight loss should seek professional help to assure a slow weight loss before competition begins.
Athletes do not need a diet substantially different from the U.S. Recommended Dietary Guidelines. However, the intake and timing of carbohydrates, protein, and fluids all affect athletic performance. The following guidelines are advised.
Meeting energy needs is the first priority for athletes, with caloric requirements influenced by many factors such as age, sex, lean body mass, and frequency and intensity of the exercise. Great variation among individuals exists in the energy needed to maintain weight and body composition. Men and women aged 19-50 years who are slightly to moderately active were established by the 1989 Recommended Daily Allowances as 2,200 and 2,900 kcal per day, respectively. However, the male endurance athlete may need as high as 5,000 kcal per day.
The body prefers carbohydrates as an energy source, using blood glucose during the first minutes of exercise. Then the stored carbohydrate form called glycogen becomes depleted to some extent, with a slow walk using up less glycogen than a one-hour jog. In endurance exercise, the energy source shifts to circulating blood glucose provided from the breakdown of fats. A diet consisting of 55%-60% carbohydrate is sufficient for most athletes, with daily recommendations ranging from 6-10 gm/kg body weight, depending on the type of sport, energy expended, sex and environmental conditions.
A practice called carbohydrate loading, which first depletes glycogen stores and then restores them with a 70% carbohydrate intake, is sometimes used in athletes performing exhausting events lasting at least 90 minutes. However, it entails weeks worth of preparation to adjust exercise and diet.
Protein and fat both contribute to the energy pool but in much less amounts. Protein needs of athletes receive a lot of attention but a balanced diet usually meets requirements. Endurance athletes and strength-training athletes do need more protein, 1.2 gm up to 1.6 gm/kg for strength training, versus the usual 0.8 to 1 gm/kg. Few athletes are protein-deficient, because the extra calories eaten due to exercise needs provide adequate protein. Research on individual amino acids supplementation is inconsistent and their use is not advocated.
As for fat, diets containing 20-25% energy from fat are recommended to ensure adequate carbohydrate intake. Because of negative effects on some people's blood lipids, fat intake should not be decreased below 15% of calories.
Vitamin and mineral supplementation is not required if a variety of foods are eaten. Calcium, iron and zinc can be low in the diets of athletes, particularly females. Of these, iron depletion is the most common, and occurs most often in female athletes, long-distance runners and vegetarians.
Fluid intake is probably the most neglected aspect of an athlete's diet. Muscle activity during exercise produces heat, which the body gets rid of through sweat. It is very important that water be replaced to prevent dehydration.
Fluid losses can exceed 2 qts (1.8 L) per hour, especially in humid environments or in sports where padding blocks effective sweating. Performance becomes impaired in dehydration. The amount of fluid needed depends on how much sweat is lost during exercise.
The use of ergogenic aids, products that claim to increase performance or work output, is controversial. Athletes should carefully evaluate products before use.
During exercise, the following guidelines should replace fluid losses and maintain carbohydrate levels. These are especially important for endurance events lasting longer than an hour or in extreme environment.
- Drink small amounts (6-12 oz) of plain, cool water every 15-20 minutes during workouts, as tolerated, particularly if it is hot or humid or during longer exercise.
- For exercise lasting over one hour or in high humidity, a sports drink like Gatorade or PowerAde, which contain 6% carbohydrate (15–20 gm or 8 oz), can maintain blood glucose levels, preserve glycogen stores, and improve performance. Beverages such as undiluted fruit juice contain greater than 8% carbohydrate and may cause intestinal upset.
The following is recommended one to two hours before exercise:
- Exercisers should eat a carbohydrate snack, such as yogurt, cereal, or a bagel one or more hours before exercise if it has been several hours since a meal. Grains, fruits and dairy products all contain high amounts of carbohydrates and help keep a steady blood sugar. People who experience stomach upset or drops in blood sugar called hypoglycemia should avoid carbohydrates immediately before exercise.
- Drink about two cups (14-22 oz) of fluid before exercise.
The following tips help after exercise:
- The athlete should drink adequate fluids to replace sweat losses. The best measurement of fluid loss is weighing before and after exercise. Drinking 16–24 oz of fluid (non-caffeinated, non-alcoholic) for every
- pound (0.45 kg) of body weight lost during exercise is recommended. If the previous meal included sodium, there is no need for an electrolyte drink after a session of moderate duration.
- Eat a high carbohydrate snack or drink some juice, when muscles are geared up to replace expended glycogen. Especially after strenuous competition or training, a snack that also contains some protein will help build and repair muscle tissue.
Vegetarian athletes may be at risk for inadequate energy, protein, and micronutrients intakes, particularly if they eliminate dairy from their diet. Consultation with a registered dietitian is recommended.
While incorrect carbohydrate or fluid intake usually leads to reduced performance, too much dehydration can be deadly. A loss of 5% of body weight due to sweating can result in heat stroke, a severe condition characterized by high fever, collapse, cessation of sweating, and sometimes coma. Hypohydration occurs when athletes dehydrate themselves before competing, such as for a weight category. Hyponatremia (low blood sodium concentrations) can develop from prolonged heavy sweating and failure to replace sodium, or when excess water is retained in the body.
Research over the past 20 years shows good nutrition affects exercise performance. Optimal sport nutrition increases glycogen stores prior to exercise, supplies carbohydrate during prolonged exercise, and assures adequate hydration before, during and after exercise.
Health care team roles
- The training of exercise physiologists includes sports nutrition. Also, athletes can seek consultations with a licensed nutrition specialist or registered dietitian trained in sport nutrition.
- Nursing and other allied health professionals should ask patients about their exercise and nutrition habits, particularly when patients present with unexplained weight loss, bone fractures or nutrient deficiencies.
Carbohydrates—Sugars or starches composed of long sugar chains, which serve as a main energy source.
Endurance athlete—An athlete who trains continuously, for long durations and over an extended period of time.
Glycogen—The main storage form of carbohydrate, which occurs primarily in the muscle and liver
American Dietetic Association, Dietitians of Canada and the American College of Sports Medicine. "Nutrition and Athletic Performance Position Paper." Med.Sci. JADA 32, no.12 (December 2000): 2130–2145. <http://www.eatright.org/adap1200.html>.
American College of Sports Medicine (ACSM). 401 W. Michigan St., Indianapolis, IN 46202-3233. (317) 637-9200. <http://www.acsm.org>.
American Dietetic Association (ADA). 216 W. Jackson Blvd., Chicago, IL 60606-6995. 800/366-1655. <http://www.eatright.org>.
Gatorade Sports Science Institute (GSSI). 617 West Main Street, Barrington, IL 60010, 800-616-GSSI (4774). <http://www.gssiweb.com>.
Nicholas Institute of Sports Medicine and Athletic Trauma (NISMAT) 2001. Lenox Hill Hospital, 100 East 77th Street, New York, NY 10021. 212-434-2000. <http://www.nismat.org>.
Linda Richards, R.D., C.H.E.S.