Effects on weight and metabolic rate of obese women of a 3.4 MJ (800 kcal) diet.

103 obese women (mean [SD] Quetelet's index [weight/height2] 38 [8] kg/m2) were admitted to a metabolic ward and were kept strictly to a diet providing 3.4 MJ (800 kcal) daily for 3 weeks. Body weight was measured daily and fasting resting metabolic rate (RMR) on days 1, 7, and 21. Both weight and RMR fell more rapidly in the first week than later. The thermic effect of feeding fell immediately on the lower energy intake, and there was an adaptive reduction of about 6% in RMR in week 1. After 3 weeks, the average weight loss was 4.9 (1.2) kg (about 5% of initial weight) and the average fall in RMR 8.8%. If after substantial weight loss a woman eats just enough to maintain energy balance the adaptive reduction in metabolic rate is restored to normal, and the thermic effect of feeding is restored in proportion to the new energy intake, but total energy requirements remain less than in the obese state to the extent that fat-free mass has been reduced. Thus, an obese woman who reduces weight by 30% over a year will thereafter have requirements for weight maintenance which are reduced by about 15%.