Weight loss in postmenopausal obesity: no adverse alterations in body composition and protein metabolism

We sought to determine if decrements in the mass of fat-free body mass (FFM ) and other lean tissue compartments, and related changes in protein metabo lism, are appropriate for weight loss in obese older women. Subjects were 1 4 healthy weight-stable obese (BMI greater than or equal to 30 kg/m(2)) pos tmenopausal women >55 yr who participated in a 16-wk, 1,200 kcal/day nutrit ionally complete diet. Measures at baseline and 16 wk included FFM and appe ndicular lean soft tissue (LST) by dual-energy X-ray absorptiometry; body c ell mass (BCM) by K-40 whole body counting; total body water (TBW) by triti um dilution; skeletal muscle (SM) by whole body MRI; and fasting whole body protein metabolism through L-[1-C-13] leucine kinetics. Mean weight loss ( +/-SD) was 9.6 +/- 3.0 kg (P< 0.0001) or 10.7% of initial body weight. FFM decreased by 2.1 +/- 2.6 kg (P = 0.006), or 19.5% of weight loss, and did n ot differ from that reported (2.3 +/- 0.7 kg). Relative losses of SM, LST, TBW, and BCM were consistent with reductions in body weight and FFM. Change s in [1-C-13] leucine flux, oxidation, and synthesis rates were not signifi cant. Follow-up of 11 subjects at 23.7 +/- 5.7 mo showed body weight and fa t mass to be below baseline values; FFM was nonsignificantly reduced. Weigh t loss was accompanied by body composition and protein kinetic changes that appear appropriate for the magnitude of body mass change, thus failing to support the concern that diet-induced weight loss in obese postmenopausal w omen produces disproportionate LST losses.