Newly updated American Academy of Pediatrics recommendations caution about unhealthy ways young athletes in "weight sensitive" sports may slim down or bulk up in hopes of achieving more competitive physiques. These risky weight losses or gains increase short– and long–term health problems and injury risk, and may even hurt athletic performance, according to the AAP.

The clinical report, "Promotion of Health Weight–Control Practices in Young Athletes," in the September 2017 Pediatrics (published online Aug. 21), says athletes in sports such as gymnastics, figure skating, and diving may believe they are judged more favorably with a lean body build. Cross–country or distance runners may think they move more efficiently against gravity by losing weight, while athletes in weight–class sports such as wrestling may try to compete at the lowest possible weight to increase strength–to–weight ratio. In contrast, football and powerlifting highlight a muscular physique, and youth in these types of sports often try to gain weight to improve performance.

"Sometimes, children and teens in certain sports believe they need to achieve a particular body type to be successful," said Rebecca L. Carl, MD, MS, FAAP, lead author of the clinical report. "Unless they have a healthy strategy to work toward their goals, however, they can end up defeating themselves and causing health problems."

Youth athletes in weight–class sports, such as wrestling, boxing, and crew, for example, may attempt to cut weight rapidly with dehydration methods such as fasting, restricting fluid intake and sweating, according to the report. Although most athletes try to rehydrate between weigh–in and competition, over the course of several days, progressive dehydration may still occur. Many athletes fail to fully rehydrate each day and replacement of intracellular fluids typically takes 48 hours.

Continued use of unhealthy weight–loss methods, in which the child's hydration or nutrition needs aren't met, can cause:

• reduced muscle strength, lower speed or less stamina in aerobic activities;
• decreased cognitive performance, such as reaction time, problem solving, alertness and accuracy;
• changes in the body's immune response and cardiovascular, endocrine, gastrointestinal, renal, and thermoregulatory systems;
• delayed physical maturation and impaired growth;
• mood changes, depression and the development of eating disorders;
• "female athlete triad," which is caused by a combination of low calorie availability, menstrual dysfunction and low bone mineral density, and can increase risk of broken bones.

Children and teens who try to gain weight for their sport can raise obesity–related risks while decreasing stamina and performance. The report recommends increased calorie consumption be accompanied by weight–training programs to encourage muscle growth rather than excess body fat. Authors also caution against dietary supplements popular with youth athletes that may contain potentially harmful ingredients.

Any change in weight and body composition should be achieved gradually, initiated early enough to permit gradual weight change while consuming a well–balanced diet before a sport season and using sensible methods aimed at long–term change, according to the AAP report. Once desired body composition and weight are achieved, dietary, exercise and lifestyle behaviors should focus on maintenance, with allowances for growth.