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How weight loss can hurt running performance

Champaign, IL—Female runners often correlate weight loss with body fat reduction when attempting to manipulate body composition and enhance performance. But, according to 2011 IDEA Personal Trainer of the Year Jason Karp, PhD, and coauthor of the Running for Women (Human Kinetics, 2012), there is little evidence that weight loss results in improved performance in already-lean athletes. “Weight loss in relatively lean female runners is detrimental to their health and can result in a loss of lean body tissue and lead to worsened performance,” Karp says. “Despite negative consequences, the desire to attain the ideal body composition to improve performance is the primary impetus contributing to the development of the female athlete triad in female endurance runners.” 

The female athlete triad was first identified as a serious health condition in 1992 and consisted of athletes with disordered eating, menstrual irregularities, and osteoporosis. By 2007 more female athletes were at risk of developing the syndrome and the definition was broadened to female athletes experiencing reduced energy, menstrual disorders, and low bone mineral density. Each component of the triad is interrelated and exists on a continuum of severity between health and disease. 

“Progression along the three continuums occurs at different rates, although it is underfueling (inadequate nutrition) for the level of physical activity that begins the cycle,” Karp explains. “Compared with other athletes, female distance runners have a higher incidence of both amenorrhea and reduced energy intake, increasing the likelihood that the triad will be present.” 

Runners with components of the triad can perform well for long periods, but eventually the physical and psychological consequences will affect a performance and well-being. “As the energy deficit continues, runners will experience a decrease in power, muscle strength, and stamina,” Karp says. “Performance gains previously seen from a well-designed training plan will no longer occur and athletes will have difficulty completing what used to be an effortless workout.” 

The most detrimental effect of the triad is continued bone loss leading to irreversible osteoporosis. Thus, resulting stress fractures will be slow to heal because of the negative nutritional balance. “Multiple fractures can lead to increased incidence of osteoarthritis depending on the site of the fractures,” Karp explains. “Frequent stress fractures will curtail running activities, and, if severe, could permanently end a running career.” 

Decreasing weight can improve performance, especially in long races, but Karp warns that modifying body composition must be done in a healthy manner. “Keeping records of body weight, menstrual function, and distance run per week will assist runners in finding the ideal body weight for health and performance,” Karp says. “If they have had a stress fracture, find their menstrual cycle has changed, or notice more frequent illnesses or injury, they should seek evaluation by a health care provider.”

For more information, see Running for Women.