MONDAY, June 20 (HealthDay News) -- Gymnasts, wrestlers and boxers often feel pressure to lose weight to boost performance, but the drastic methods they sometimes use -- including strictly limiting calories and intentional dehydration -- can be dangerous to their health, experts warn.

To offer guidance to athletes, coaches and parents, the National Athletic Trainers' Association has issued a new set of guidelines for safe weight loss by athletes.

They include: using body composition assessments to measure lean body mass versus fat; gradually shedding no more than 1.5 percent of body weight a week; eating a balanced diet that includes all food groups; and losing weight under the supervision of nutrition, health and weight management experts.

"In the performance sports -- gymnastics, dance, ballet -- they have this huge responsibility to not only do a performance but to look good while they are doing it. It's a unwritten rule that they have to be a certain weight, and they get a lot of pressure, not just from dance masters but from the public's expectations and themselves," said Paula Sammarone Turocy, lead author of the guidelines and chair of the department of athletic training at Duquesne University in Pittsburgh. "We also see it in traditional sports -- jockeys, wrestlers, boxers. They all have weight requirements. If they don't make the weight, they don't compete."

And the pressure to shed weight cuts across all sports, she added. Many cyclists, swimmers, runners, soccer players and even football players believe that losing weight will mean they can run, swim and jump faster.

Getting down to an ideal body weight to improve performance isn't a problem in and of itself, she said. It's when athletes go to extremes that their drive can backfire. "When it's done improperly or done to extremes it does interfere with performance," she explained.

The new guidelines were to be presented Monday at the annual meeting of the National Athletic Trainers' Association in New Orleans and are published in the June issue of the Journal of Athletic Training.

Ashleigh Clare-Kearney has been there. As a high school student, she was a standout gymnast, in more ways than one. She was powerful and graceful, although she was 5-foot-4 and weighed 155 pounds.

"I didn't fit the stereotypical frame, which is 4 feet, 10 inches, 110 pounds," Clare-Kearney said. "I was told, 'You need to lose weight. You will be viewed as a risk. You are not going to be able to compete in elite international competitions.' People said I wouldn't make it because of my size."

She defied their predictions. As a gymnast at Louisiana State University (LSU), she became the NCAA national champion in vault and floor, captain of the team and a NCAA Woman of the Year finalist.

Yet she couldn't deny it -- slimming down would help her performance. She'd put on weight when she got to college, and she knew that carrying less heft might allow her to vault even higher.

Working with the athletic trainers and the coaches at LSU, she got down to about 145 pounds by focusing on nutrition. "I was never going to be 110 pounds. That's not the way I'm built," she said. "What really resonated with me was the way the athletic training staff understood that. They said, 'Let's be realistic.'"

For Clare-Kearney, that included keeping a food diary, making sure to always eat breakfast, drinking water instead of sweetened beverages and eating more fruits and vegetables and less processed foods.

But not every athlete manages to handle the pressure to lose weight so well.

Before competitions, some wrestlers, jockeys and boxers intentionally dehydrate themselves by exercising in heavy clothing and restricting certain foods and fluids to lose weight quickly.

There are even anecdotal reports that elite, international athletes have their blood removed by IV prior to weigh-in. The blood is then re-infused before competition.

Among wrestlers at least, intentional dehydration may be less popular than it used to be due to changes in the rules from the high school level on up that call for urine tests to detect hydration status at weigh-in. In 2006, for example, the National Federation of State High School Associations not only adopted the hydration status rules, but also minimum body fat requirements (greater than 7 percent in boys and 12 percent in girls) in order to compete.

Not only can rapid weight loss hurt performance over the short term because athletes simply don't have the energy to perform at their best, but experts add that restricting calories can also have long-term consequences.

Over time, dietary restrictions can impact the endocrine system, hindering the growth and functioning of muscles and bones. A poor diet can also impair thyroid function, lower metabolism and hormone production and suppress the immune system.

Clare-Kearney, now a law student at Southern University Law Center of Baton Rouge and a volunteer coach for her alma mater, urges young athletes to consider the consequences of their diets.

"Food really does fuel your body. Your body can only handle so much without the proper fuel and nutrition," she said. "And there is life beyond gymnastics. We also have to keep our body healthy for life after gymnastics."

More information

The U.S. National Institute of Mental Health has more on eating disorders.