Twenty-four hour energy expenditure (24EE) and spontaneous physical activity were measured in 13 overweight women before and at the end of an 8-wk slimming period. These measurements were repeated in 10 women 1 mo after the slimming period (1-mo follow-up) and in eight women 1 y after slimming (1-y follow-up). The weight loss achieved after 8 wk of slimming (8.7-9.9 kg) was maintained throughout the follow-up periods; 24EE decreased during slimming from 9572 +/- 703 (means +/- SD) to 8060 +/- 471 kJ/d and increased after refeeding to 8379 +/- 739 kJ/d after 1 mo and to 8285 +/- 454 kJ/d after 1 y. On the basis of body weight, energy requirement (approximately 126 kJ.kg-1.d-1) did not change throughout the slimming and follow-up programs. Spontaneous physical activity, which had been lowered during slimming, tended to increase afterwards. No changes in metabolic efficiency seemed to occur or persist.