Strict dieting may harm young runners' bone health

By Joene Hendry

NEW YORK (Reuters Health) - Teenage girls who stringently restrict their energy intake while involved in endurance sports may end up with low bone density, researchers report.

Preliminary evidence from a study involving 93 female high school cross-country runners shows an association between low bone mass values and more intensive dietary restraint, according to a report in the American Journal of Clinical Nutrition.

Michelle T. Barrack, at the University of California, Davis, and colleagues assessed the level of dietary restraint reported among these 13-to-18 year-old athletes by determining the girls' attempts to influence shape or weight during the previous month.

The investigators defined high levels of dietary restriction as girls who reported not eating for 8 hours or more, consciously restricting amounts or types of food, and following strict calorie or serving size limits for 16 days or longer during the month, Barrack said.

She and her colleagues compared these reports with measurements of the girls' bone mineral density in the lower spine and thighbone.

"Girls reporting elevated dietary restraint exhibited the lowest bone mass values," Barrack told Reuters Health. By contrast, she noted that weight or shape concerns in the absence of dietary restraint practices were not associated with low bone mass.

The researchers also saw a trend toward a higher rate of menstrual irregularity among the runners reporting higher levels of dietary restraint.

Inadequate calorie intake, especially among already lean individuals, can alter hormones that regulate bone metabolism as well as menstrual function, Barrack noted.

"These findings suggest that young runners and their support system, including parents, coaches, and athletic trainers, should make sure that girls expending hundreds of calories on a daily basis are not stringently restricting their energy intake," Barrack said.

SOURCE: American Journal of Clinical Nutrition, January 2008