Effect of weight reduction on resting energy expenditure, substrate utilization, and the thermic effect of food in moderately obese women.

It is not known whether the decrease in the thermic effect of food (TEF) in obesity is a consequence of obesity or a factor contributing to the development of obesity. The resting energy expenditure (REE) of 24 obese, nondiabetic, postmenopausal women was 5481 +/- 110 kJ/24 h (1310 +/- 26.4 kcal/24 h). After weight loss (12.7 +/- 0.45 kg) the REE was significantly decreased (4858 +/- 94 kJ/24 h, or 1161 +/- 22.4 kcal/24 h) and equivalent to the REE of 4866 +/- 119 kJ/24 h (1163 +/- 28.5 kcal/24 h) in 24 never-obese, postmenopausal women. The TEF, expressed as a percentage of the calories ingested, was 8.2 +/- 0.50% for obese subjects, 8.7 +/- 0.57% for postobese subjects, and 9.8 +/- 0.54% for never-obese subjects. Compared with never-obese subjects, the TEF was significantly reduced in obese subjects (P = 0.043) and remained unchanged after weight loss (P = 0.341). These findings indicate that the lower TEF in the obese subjects is uncorrected by weight loss, and thus it is a contributor to obesity rather than a consequence of obesity.