Am Fam Physician. 2006;73(11):2069-2074
Children and adolescents often are involved in sports in which weight loss or weight gain is perceived as an advantage. To address counseling issues that physicians may encounter in caring for these patients, the American Academy of Pediatrics (AAP) has released recommendations on healthy weight-control behaviors in young athletes. The full report was published in the December 2005 issue of Pediatrics.
Many athletes attempt to lose weight or body fat with the hope of meeting weight expectations or improving their performance or appearance. Methods include food restriction, self-induced vomiting, overexercising, use of diet pills or nicotine, inappropriate use of prescribed stimulants or insulin, and voluntary dehydration (e.g., fluid restriction, spitting, use of laxatives, diuretics, or saunas). These methods, which may be practiced year-round or only during the sport season, can impair athletic performance and increase risk of injury. They also may result in complications such as delayed physical maturation; oligomenorrhea and amenorrhea; eating disorders; increased incidence of infectious diseases; depression; and changes in the cardiovascular, endocrine, gastrointestinal, renal, and thermoregulatory systems. Weight loss becomes a problem when nutritional needs are not met or adequate hydration is not maintained (see accompanying table).
Because the body does not store fluid or electrolytes before exercise, it is predisposed to dehydration. The extent of dehydration is determined by sweat loss and the inability or refusal to replace those losses with oral intake of fluids.
Thirst is a late indicator of dehydration in adolescents and adults; therefore, efforts must be made to maintain euhydration. Recent studies suggest that children's thirst is inadequate and that they become dehydrated more easily than adults. The best way to assess hypohydration is to weigh the athlete before and after exercise. For every pound of weight lost, the athlete should consume 1 pt (473 mL) of fluids before the next exercise session. The fluids should contain sodium chloride and carbohydrates to replenish glycogen stores.
Involuntary dehydration may occur with prolonged exercise even if the child is given fluids ad libitum. This generally occurs when the fluids are unflavored. When children are given plain water, they will not replace their fluid losses completely. However, when they are given flavored drinks, voluntary drinking increases by 44.5 percent, which is sufficient to completely replace their fluid losses. The concentration of sodium in sports drinks is lower than the sodium concentration in sweat; therefore, even if children drink enough sports drinks to maintain euhydration, their total body sodium levels will be decreased. If this process is repeated over several days and the sodium is not replaced by food or drink, symptomatic hyponatremia may develop.
Compared with adults, children have a considerably lower sweating capacity, which reduces their ability to dissipate body heat by evaporation. Children also have a greater ratio of body surface area to body mass, which causes them to absorb heat more quickly when the ambient temperature exceeds skin temperature. Thus, a high level of solar radiation can be more detrimental to children than to adults.
Dehydration over several days may be cumulative when an athlete does not replace his or her fluid losses sufficiently. An athlete may develop 2 to 3 percent hypohydration one day, not fully hydrate overnight, and then dehydrate further on subsequent days. This progressive dehydration can lead to hypohydration of 5 to 8 percent of body weight. The greater the body-fluid deficit, the longer it takes to completely restore this deficit. Replacement of intracellular fluids requires 48 hours when dehydration has occurred over two or three days.
The most common way for athletes to attempt weight loss is by restricting food intake. This may lead to disordered eating behaviors such as purging, with or without bingeing, to decrease total caloric intake. The spectrum of these disordered eating behaviors ranges from mild to severe. Compulsive or excessive exercise in addition to the normal training regimen is considered a form of purging.
Disordered eating behaviors are prevalent in athletes: 10 to 15 percent of high school boys who participate in “weight-sensitive” sports (e.g., wrestling, diving, swimming, long-distance running) practice unhealthy weight-loss behaviors, and in one study investigators found that 11 percent of wrestlers have an eating disorder. Many studies have shown an increased incidence of disordered eating behaviors in female athletes who participate in weight-sensitive sports. All female athletes with oligomenorrhea or amenorrhea should be evaluated thoroughly to determine the underlying etiology. If low energy availability is the cause, the athlete should be counseled to increase caloric intake enough to resume normal menses. If an eating disorder is suspected, referral to a multidisciplinary team is appropriate.
Healthy Weight Loss
Athletes usually require a greater caloric intake than nonathletes. The actual amount of calories needed depends on the athlete's body composition, weight, height, age, stage of growth, and level of fitness, as well as the intensity, frequency, and duration of exercise. Athletes who want to lose weight should be counseled on the harmful effects of unhealthy weight-loss practices and inappropriate weight loss. They should be informed that weight is not an accurate indicator of the amount of body fat or lean muscle mass and that body composition measurements can be much more helpful.
Studies have shown that physique does not markedly influence athletic performance except at the extreme ranges (i.e., significant endomorphy or ectomorphy). An excessive amount of body fat interferes with acclimation to heat and can decrease speed, endurance, and work efficiency. Therefore, weight loss may be beneficial when it is achieved by healthy means and involves losing excess fat without reducing lean muscle mass or causing dehydration. When weight is lost too rapidly or by significant reduction in caloric intake, lean muscle mass will be lost, which can negatively affect athletic performance.
Weight loss, when necessary, should be gradual and should not exceed 1.5 percent of total body weight or 1 to 2 lb (0.45 to 0.91 kg) per week. Weight loss beyond these limits results in the breakdown and metabolism of muscle. To lose 1 lb of fat in one week, a person must expend 3,500 kcal more than he or she consumes. The ideal way to do this is to consume 1,750 fewer calories and expend 1,750 more calories per week by exercising. An appropriate diet for most athletes consists of at least 2,000 kcal per day; 55 to 65 percent of these calories should be from carbohydrates, 15 to 20 percent should be from protein, and 20 to 30 percent should be from fats.
Once weight has been lost and the desired weight attained, that weight should be maintained. Studies have shown that athletes who maintain their desired weight have higher resting metabolic rates than do athletes who are cyclic weight losers. They also have higher resting energy expenditures and oxygen consumption. Therefore, athletes who maintain a constant weight can eat more calories than cyclic weight losers and maintain the same weight.
Healthy Weight Gain
Sports such as football, rugby, basketball, power lifting, and bodybuilding often motivate athletes to gain weight. If weight is gained improperly, it will lead to excess fat, resulting in decreased speed, endurance, and agility. Overweight athletes are at greater risk in later life for hypercholesterolemia, gallbladder disease, cardiovascular disease, hypertension, and type 2 diabetes. Before trying to change their body composition, athletes must understand potential genetic limitations. Athletes with a solid body build may expect to gain more weight than athletes with a slender build. Inadequate caloric intake often is the limiting factor for athletes trying to increase muscle mass; they may overestimate protein requirements and underestimate the need for carbohydrates.
To build 1 lb of muscle in one week, a person must consume 2,000 to 2,500 kcal more than he or she expends, consume 1.5 to 1.75 g of protein per kg of body weight per day, and participate in strength training. Increased caloric intake must be combined with strength training to induce muscle growth; gains in muscle hypertrophy are best achieved by performing multiple sets of weight lifting with a relatively high number of repetitions (i.e., eight to 15 repetitions per set). Young athletes should lift lighter weights for more repetitions under the supervision of a trained adult.
Weight gain must be gradual; a gain of more than 1.5 percent of body weight per week may result in unwanted fat. If the athlete has not gained the desired weight despite an appropriate training program, adequate rest, and a nutritionally sound diet, it is appropriate to recommend that he or she increase levels of dietary fats. Studies of elite athletes have found dietary fat intakes ranging from 29 to 41 percent in males and 29 to 34 percent in females.
All physical examinations of young athletes should include a weight history and a history of eating patterns, hydration practices, eating disorders, heat illness, and other factors that may influence heat illness or weight control. Physicians should be able to recognize early signs of eating disorders and obtain appropriate medical, psychological, and nutritional consultation for young athletes with these symptoms.
Athletes must consume enough fluids to maintain euhydration. Any athlete who loses a significant amount of fluid during sports participation should weigh in before and after practices, games, meets, and competitions. Each pound of weight lost should be replaced with 1 pt of fluid containing carbohydrates and electrolytes before the next practice or competition.
Nutritional needs for growth and development must be placed above athletic considerations. Fluid or food deprivation should never be allowed. There is no substitute for a healthy diet consisting of a variety of foods from all food groups with enough calories to support growth, daily physical activities, and sports activities. Daily caloric intake for most athletes should consist of a minimum of 2,000 kcal.
Male high school athletes should not have less than 7 percent body fat. This level may be too low for some athletes and result in suboptimal performance. Female athletes should consume enough calories and nutrients to meet their energy requirements and have normal menses. There are no recommendations for body-fat percentage in female athletes.
A program for gaining or losing weight should be started early to permit a gradual weight gain or loss over a realistic period (i.e., up to a maximum of 1.5 percent of body weight per week). Weight-gain and weight-loss programs should be coupled with an appropriate training program and incorporate a well-balanced diet with adequate intake of calories, carbohydrates, protein, and fats. After athletes attain their desired weight, they should be encouraged to maintain a constant weight and avoid fluctuations in weight. A weight-loss plan for athletic purposes should never be started before the ninth grade.
Weight loss accomplished by overexercising; using rubber suits, steam baths, or saunas; prolonged fasting; fluid reduction; self-induced vomiting; or using anorexic drugs, laxatives, diuretics, diet pills, insulin, stimulants, nutritional supplements, nicotine, or other drugs should be prohibited at all ages.
In sports for which weigh-ins are required, athletes' weight and body composition should be assessed once or twice per year. The most important assessment is obtained before the start of the sport season. This should include a determination of body fat percentage and minimal allowable weight when the athlete is adequately hydrated. Weigh-ins for competition should be performed immediately before the competition. Athletes should be permitted to compete in championship tournaments only at the weight class in which they have competed for most other athletic events that year.