Bone loss accompanying diet-induced or exercise-induced weight loss: a randomised controlled study.

OBJECTIVE: To compare the effects of two weight loss interventions, diet or exercise, on changes in bone, fat and lean tissue. DESIGN: Prospective, long term, worksite, randomised and controlled weight-loss study using a low fat diet ad libitum or moderate aerobic exercise. SUBJECTS: 66 overweight men (mean age 43.4 +/- 5.7 y, BMI 29.0 +/- 2.6 kg/m2). MEASUREMENTS: Body weight, lean mass, fat mass, bone mass (BMC), bone mineral density (BMD) by dual-energy X-ray absorptiometry. RESULTS: Dieters lost 1.4% BMC (1.5% BMD) with 6.4 kg weight loss; there was no significant change in BMC (or in BMD) in exercisers (2.6 kg weight loss) or in control subjects (no weight change). Changes in BMC were correlated with fat loss with both interventions: 11.7 g BMC/kg fat loss in dieters, 11.4 g BMC change/kg fat loss in exercisers. CONCLUSION: BMC loss with diet-induced weight loss reflects loss of weight and especially loss of body fat. Further study to determine whether similar BMC loss will accompany equivalent weight loss induced by exercise is needed.