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The Effects of Exercise and Diet on Young Women's Bone Health

For some, dieting could almost be considered a hobby, particularly among younger women. We've heard it's better not to be overweight, but what are the health downsides on the road to achieving ideal body weight? These researchers intended to determine the effects of dieting practices and exercise on bone health.

Specifically, they examined the effect of dietary restraint--a type of dieting guided by a mental awareness of the types and amounts of food eaten, not simply by feelings of hunger or fullness. Scientists have found that women with high measures of dietary restraint often show disturbances in their menstrual cycles. These women also tend to consume fewer calories than others with low dietary restraint.

Problems with the menstrual cycle aren't always obvious. In other words, the individual may still have a period as usual. Behind the scenes, however, there can be measurable changes in hormones, including those that help build bone. Scientists have found a definite connection between menstrual disturbances and lower bone density.
 
Exercise helps build bone, but is it enough to counter the effects in women with high dietary restraint? This study compared 62 women, most in their early 20s, all of whom exercised two to four hours a week. From the results of a diet questionnaire, they were grouped as either "high restraint" or "low restraint" eaters. Both groups had regular menstrual cycles and similar body composition.
 
The bone mineral content of the high restraint group was significantly lower than that of the low restraint group. This was true even though those with higher dietary restraint exercised more each week than low restraint eaters. The authors consider whether this difference was from higher levels of cortisol in the blood stream of high restraint eaters.

How does cortisol play into bone health? Cortisol is released into the body during times of stress. High dietary restraint poses stress on the body. As cortisol levels in the blood stream go up, they signal a reduction in other hormones that are in charge of ovulation and menstruation. This causes the body to absorb less calcium, which in turn lowers bone mass.

The authors conclude that high dietary restraint and higher levels of cortisol may lessen the positive effects of exercise on bone health in younger women.

References: Judy A. McLean, Susan I. Barr, and Jerilynn C. Pryor. Dietary Restraint, Exercise, and Bone Density in Young Women: Are They Related? In Medicine & Science in Sports & Exercise. August 2001. Vol. 33. No. 8. Pp. 1292-1296.

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