Objective: To analyze the relationship between visceral fat accumulation and resting energy expenditure in obese women and to evaluate the effects of a severe weight loss both on energy expenditure and on fat distribution.
Design: Twelve premenopausal women, aged 19-50 years, undergoing adjustable silicone gastric banding (ASGB) for morbid obesity participated at the study. The patients were evaluated twice. The baseline evaluation was performed immediately before surgery. After surgery, a diet specifically developed for patients submitted to gastric restriction (2.5 MJ/day) was given to the patients. The second evaluation was performed 6 months after surgery.
Measurements: Resting metabolic rate (RMR) was determined by indirect calorimetry. Total fat area (TFA), visceral fat area (VFA) and subcutaneous fat area (SFA) were measured by abdominal computed tomography. Fat mass (FM) and fat free mass (FFM) were derived by bioelectrical impedance analysis.
Results: At baseline, RMR was positively related to VFA (r = 0.60, P < 0.05). ASGB induced a highly significant weight loss of 24.4 +/- 9.0 kg. This weight reduction was mainly due to a loss of FM (68.5 +/- 10.8 vs 48.5 +/- 9.2 kg, P < 0.001), whereas FFM was only slightly reduced (52.6 +/- 4.0 vs 47.9 +/- 4.6 kg, P < 0.05). The BMI reduction was positively related to the baseline BMI and FM values (r = 0.61, P < 0.05 and r = 0.55, P < 0.05, respectively). There was no significant correlation between the BMI reduction and the baseline variables of fat distribution, nor between the BMI reduction and the basal RMR. Weight loss was accompanied by modifications of fat distribution. In particular, the reduction of VFA after surgery was strictly related to the VFA values at baseline (r = 0.91, P < 0.001). Weight loss induced a significant reduction of RMR (7.96 +/- 1.77 vs 6.57 +/- 6.90 MJ/day; P < 0.01). The reduction of the RMR observed with weight loss was significantly related to the FFM loss (r = 0.63, P < 0.05), whereas no correlations were found between the changes of RMR and the FM loss. Regarding to fat distribution, the reduction of the RMR was significantly related to the visceral fat loss (r = 0.57, P < 0.05), but not to the modifications of total or subcutaneous fat area. The independent contribution of the modifications of FFM, FM, and visceral fat to the changes of RMR was analyzed by multiple regression analysis. In this model, both FFM and visceral fat changes resulted independently related to the RMR.
Conclusions: (1) visceral fat accumulation was a significant predictor of RMR in the very obese woman; (2) visceral obese women lost more visceral fat than subcutaneous ones; (3) the reduction of the RMR observed during weight loss could partly be explained by a reduction of visceral fat mass.