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.