Correlation between the rate of weight loss and changes in body composition in obese postmenopausal women after 5 weeks: a pilot study.

Approximately 25% of weight lost during restrictive diets (without exercise) is lean body mass (LBM). No study has yet investigated the impact of the rate of weight loss (RWL) on LBM and fat mass (FM). The purpose of this study was to investigate the relationships between the RWL and body composition in older obese women. Twenty obese postmenopausal women aged between 51 and 74 years enrolled in a 5 week dietary weight loss intervention. Subjects were characterized according to their RWL (low RWL < 0.74 kg.week(-1) (n = 9) vs. high RWL > or = 0.74 kg.week(-1) (n = 11)). Total and trunk FM and LBM (by dual-energy X-ray absorptiometry) were measured before and after weight loss. A significant correlation was observed between the RWL (kg.week(-1)) and changes in LBM (kg.week(-1)) (r = 0.75; p = 0.0002). However, no association was observed with changes in FM (kg.week(-1)) (r = 0.40; p = 0.08). Both groups showed a similar decrease in FM (low RWL, -2.7 +/- 0.9 kg,; high RWL, -3.2 +/- 0.8 kg; p = 0.38), whereas losses in LBM were significantly higher in the high RWL than in the low RWL group (-1.6 +/- 1.2 kg vs. -0.4 +/- 1.1 kg; p = 0.05). An RWL > 0.74 kg.week(-1) was associated with a greater loss of LBM, but had no extra benefits on FM after a 5 week weight loss program. Current guidelines, which recommend RWL up to 0.91 kg.week(-1), might not be optimal to prevent decreases in LBM in postmenopausal women when no exercise is added.