For many years, experts have investigated the effects of low body fat on menstrual cycles in women. Some women with low body fat percentages report several irregularities, including infrequent periods, abnormally painful periods and even no period at all. Before beginning a weight-loss diet or training for your next endurance event, it's important to know just how low you can go before menstrual dysfunction occurs.
The Magic Number
Scientists have attempted to identify specific body fat percentages at which monthly cycles become disrupted. In a 1987 study published in "Sports Medicine," researchers debunked the theory that maintenance of body fat percentage of 17 to 22 percent were necessary to maintain normal menstrual function. This same study and others published since then have been unsuccessful in finding a specific cut off point but recognize that low body fat contributes to amenorrhea -- the absence of menstruation.
Researchers from Texas A&M and Ball State University estimate the prevalence of infrequent and absent periods to be around 10 and 2 percent, respectively. In athletes, generally those who train for long hours and at high intensities, those numbers increase to 40 and 5 percent, respectively. This suggests that body fat percentage may not be the only factor influencing regular menstrual function.
Fat cells contribute to nearly 1/3 of estrogen levels in your body. Because of this, low body fat may contribute to low estrogen secretion and subsequent menstrual dysfunction. Low-calorie diets and inadequate nutrition that causes energy deficits are thought thought to be the primary cause of menstrual dysfunction rather than simple low body fat, according to Dr. Anne Loucks of Ohio University.
While it is important to note with your physician, few long-term affects have been reported in association with amenorrhea in conjunction with the use of birth control devices and medicines. According to the American College of Sports Medicine, the essential body fat range -- the lowest the body can tolerate without potential widespread adverse effects -- is 8 to 12 percent in females.
- "ACSM's Resource Manual for Guidelines for Exercise Testing and Prescription"; American College of Sports Medicine; 2006
- "Physiology of Sport and Exercise"; Jack Wilmore, David Costill; 2004
- "Journal of Applied Physiology"; Low Energy Availability, Not Stress of Exercise, Alters LH Pulsatility in Exercising Women; A.B. Loucks, M. Verdun, E.M. Heath; August 1998
- "Sports Medicine"; Body Composition and Menstrual Function in Athletes; W.E. Sinning, K.D. Little; Jan.-Feb. 1987