Body Composition and Metabolic Changes following Bariatric Surgery: Effects on Fat Mass, Lean Mass and Basal Metabolic Rate: Six Months to One-Year Follow-up

Background: With the failure of traditional weight loss plans, bariatric surgery has become the treatment of choice for morbid obesity. The primary objective of this study was to track body composition and metabolic changes for 1 year following bariatric surgery. Methods: 19 bariatric patients (14 female, 5 male) began the study and completed 12 months of testing, which included data collection within 1 week preoperatively and 1, 3, 6 and 12 months postoperatively. 2 female subjects were lost to the study between 6 months and 1 year, resulting in 17 subjects (12 female, 5 male) completing the entire 12-month follow-up. Variables measured in this study included weight, lean body mass (LBM), fat mass (FM), % body fat and basal metabolic rate (BMR). Results: Analysis of variance (ANOVA) using the general linear model indicated significant (P<.05) losses for weight, FM, and % fat for all time periods. Significant losses in LBM were observed in all time periods except 6-12 months, where no change in LBM (60.6 vs 61.1 kg) was observed. A significant decrease (P<.05) in BMR (2091 vs 1758) was observed only from pre-surgery to 1 month post-surgery. Thereafter, there was no significant change in BMR (1758 vs 1647 vs 1651 vs 1674) respectively. Changes in LBM were correlated with changes in BMR at both 6-12 months (r=.545, P=.024) and preoperatively to 12 months postoperatively (r=.608, P=.01). There were no significant changes in the BMR/LBM ratio over the 12-month period (28.3 vs 25.0 vs 27.3 vs 27.2 vs 27.4), indicating no adaptation of the body to an energy-conserving mechanism. Conclusion: Bariatric surgery appears to have been highly successful over the 12-month follow-up period, with 50.9 kg weight loss, 38.3 kg (75.2%) FM loss, and 12.6 kg (24.8%) LBM loss. The 417 kcal loss in BMR (2091 to 1674), while significant, was not greater than what would be predicted from loss of LBM.