Even girls who don't have an eating disorder may still be burning far more calories than they consume, especially if they are endurance athletes. Caloric imbalance can lead to low bone mineral density (BMD), both by depriving bone of essential nutritional building blocks and by depleting levels of bone-stabilizing estrogen. Best known as a precursor to osteoporosis, low BMD can also be a risk factor for musculoskeletal injuries.
In particular, low BMD was associated with nearly five times the risk of shin injuries ... which can keep an athlete sidelined for weeks.
"If you can keep athletes eating well, they may be less likely to get injured," said Mitchell J. Rauh, PhD, PT, MPH, an associate professor at Rocky Mountain University of Health Professions and adjunct research professor in the School of Exercise & Nutritional Sciences at SDSU. "Nutrition can affect menstrual function as well as BMD. And if BMD is decreasing, that probably means other musculoskeletal tissues are more susceptible to injury as they may not be receiving adequate nutrition to repair from training demands."
Investigators from San Diego State University found that of the 94 female high school cross-country and track athletes they studied, those with low bone mineral density were more than six times more likely to suffer a lower extremity injury than those with normal BMD levels, a statistically significant difference. In particular, low BMD was associated with nearly five times the risk of shin injuries, including tibial stress fractures and shin splints, which can keep an athlete sidelined for weeks. The findings were presented in February at the annual Combined Sections Meeting of the American Physical Therapy Association.
Low BMD is one of the three components of the syndrome known as the Female Athlete Triad; menstrual dysfunction is another. Disordered eating (typically anorexia or bulimia) was originally the third component, but in October 2007 the American College of Sports Medicine recommended that be replaced by the broader "low energy availability," emphasizing that caloric imbalance should be a concern even in the absence of poor body image.
Although the triad is commonly associated with figure skaters, gymnasts, and others in so-called aesthetic sports, the SDSU findings underscore that the syndrome also applies to endurance athletes and others who simply burn through calories at a rapid rate. Such athletes may not even realize that they are at risk for low energy availability.
As an added incentive for aspiring athletes to eat well, balancing caloric intake with output may also improve performance. Olympic medalist Dara Torres has said she wasn't able to maximize her swimming potential until overcoming an eating disorder that she developed in college.
"Maintaining that energy balance is likely good for performance too," Rauh said. "I think some coaches tend to miss that."