Determinants of weight loss after vertical banded gastroplasty.

Weight loss after gastric partition is highly variable even when the operation itself has been successful. We studied changes in body composition in relation to energy expenditure before and one year after surgery in one woman and five men, age 20-38 years, and BMI 42-62 kg/m2. Observations were performed shortly before, and 6, 12, 27 and 54 weeks after surgery. Body composition was measured with hydrostatic weighing and isotope dilution, and energy expenditure over 24 h (24EE) and during complete rest (sleeping metabolic rate (SMR)) with a respiration chamber and in five of the six subjects under daily living conditions over two-week intervals with doubly labeled water (average daily metabolic rate (ADMR). Weight loss and fat loss over the full observation period until 54 weeks after surgery was 54 +/- 8 and 43 +/- 9 kg (mean +/- s.e.m.), respectively. There was a more than three-fold difference in fat loss between the subject losing most, i.e. 70 kg, and the subject losing least, i.e. 20 kg. Fat loss was not related to initial fat mass in this group of six subjects but there was a significant negative relation with the loss of protein mass. There was a strong negative relation between fat loss and activity level of the subjects expressed as the quotient ADMR/SMR. These results show the contrary from what would be expected. Reduction of fat mass after successful gastric partition is highest in those subjects having the lowest physical activity level (before and) after surgery; these subjects lose less fat-free mass.