ENERGY-METABOLISM IN WEIGHT-STABLE POSTOBESE INDIVIDUALS

A low metabolic rate for a given body size and body composition and a low ratio of fat to carbohydrate oxidation predict body weight gain. S uch metabolic traits could also explain, in part, the propensity of pr eviously obese (postobese) individuals to regain weight after dieting. We studied 11 postobese volunteers (4 males, 7 females; aged 43 +/- 1 3 y, weighing 80.6 +/- 10.2 kg, with 30 +/- 7% body fat; (x) over bar +/- SD) who lost 57 +/- 38 kg (23-139 kg) over 14 +/- 12 mo (6-48 mo) on various diet programs and had maintained this weight loss for great er than or equal to 2 mo (2-72 mo; 21 +/- 27 mo). After greater than o r equal to 2 d of a weight-maintenance diet on a metabolic ward, 24-h energy expenditure and ratio of fat to carbohydrate oxidation were mea sured in a respiratory chamber. Compared with a central group (n = 110 ) with similar physical characteristics (aged 43 +/- 14 y, weighing 79 .5 +/- 11.4 kg, with 30 +/- 12% body fat), postobese individuals had s imilar energy expenditures adjusted for fat-free mass, fat mass, age, and sex, but significantly higher respiratory quotients over 24 h (0.8 83 +/- 0.026 compared with 0.863 +/- 0.024, P < 0.01) and during sleep , 10 h after the last meal (0.894 +/- 0.063 compared with 0.845 +/- 0. 055). These results suggest that postobese individuals have low rates of fat oxidation that may explain their propensity to regain weight. T herefore, obesity treatment and/or prevention should be aimed at reduc ing dietary fat and increasing fat oxidation (possibly by exercise) to prevent increases in body fat stores.