Effect of a lifestyle intervention on bone mineral density in premenopausal women: a randomized trial

Background: The positive association between body weight and bone mineral density (BMD) is well documented; in contrast, the effect of changes in body weight on BMD is not well understood, particularly, in normal-weight populations. Objective: We examined the effect of a lifestyle intervention aimed at lowering dietary fat intake and increasing physical activity to produce modest weight loss or prevent weight gain on BMD in a population of 236 healthy, premenopausal women aged 44-50 y. Design: All women were participating in a clinical trial known as The Women's Healthy Lifestyle Project and were randomly assigned to intervention or control groups. Dual-energy X-ray absorptiometry of BMD at the lumbar spine and proximal femur were made before and after 18 mo of participation in the trial. Results: The intervention group (n = 115) experienced a mean (+/-SD) weight loss of 3.2 +/- 4.7 kg over the 18 mo compared with a weight gain of 0.42 +/- 3.6 kg in the control group (n = 121) (P < 0.001). The annualized rate of hip BMD loss was 2-fold higher (P < 0.015) in the intervention group (0.81 +/- 1.3%) than in the control group (0.42 +/- 1.1%); a similar, although nonsignificant pattern was observed for the loss in spine BMD: 0.70 +/- 1.4% and 0.37 +/- 1.5% (P = 0.093) in the intervention and control groups, respectively. Large increases in physical activity attenuated spine BMD loss, but had no significant effect on BMD loss at the hip. Conclusions: The intervention group, who modified their lifestyle to lose weight, had a higher rate of BMD loss at the hip and lumbar spine than did the weight-stable control group. Recommendations for weight loss must be made with consideration that such an endorsement may result in BMD loss.