Dynamics of change in total and regional body composition after gastric bypass in obese patients.

Little is known on patterns of change over time in body composition, especially lean body mass (LBM), during massive weight loss after Roux-en-Y gastric bypass (RYGB) in obese patients. We performed sequential measurements of total and regional body composition in patients after RYGB, and we compared a subsample of patients after surgery to a nonsurgical control group of similar age and body fatness. We used dual-energy X-ray absorptiometry (DXA) before and at 3, 6, and 12 months after RYGB in 42 obese women (before surgery: age 39.5 +/- 11.6 years; BMI 44.6 +/- 6.1 kg/m(2); mean +/- s.d.) and in 48 control obese women referred for nonsurgical weight management, before weight loss. During 1-year follow-up after RYGB, there was a continuous decrease in body weight (-36.0 +/- 12.5 kg at 1 year), total fat mass (FM) (-26.0 +/- 9.1 kg), as well as in trunk and appendicular FM. In contrast, the decrease in total LBM (-9.8 +/- 4.8 kg at 1 year), as well as in trunk and appendicular LBM, plateaued after 3-6 months. Rates of loss in weight, FM, and LBM were highest during the first 3-month period after RYGB (6.4 +/- 1.8, 4.1 +/- 1.7, and 2.3 +/- 1.2 kg/month, respectively), then decreased continuously for FM but plateaued for LBM. There was no evidence of a decrease in total, trunk, or appendicular LBM in weight-reduced subjects compared to the control group. In conclusion, follow-up of these obese women revealed a differential pattern of change in FM and LBM after RYGB. Despite an important loss in LBM, especially during the 3-6 months of initial period, LBM appears to be spared thereafter.