Body composition assessment in extreme obesity and after massive weight loss induced by gastric bypass surgery

1 Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston 02111; 2 New England Medical Center Hospital, Boston 02111, Massachusetts; and 3 Body Composition Unit, St. Luke's-Roosevelt Hospital Center, New York, New York 10025 Body composition methods were examined in 20 women [body mass index (BMI) 48.7 ± 8.8 kg/m 2 ] before and after weight loss [ 44.8 ± 14.6 (SD) kg] after gastric bypass (GBP) surgery. The reference method, a three-compartment (3C) model using body density by air displacement plethysmography and total body water (TBW) by H 2 18 O dilution (3C-H 2 18 O), showed a decrease in percent body fat (%BF) from 51.4 to 34.6%. Fat-free mass hydration was significantly higher than the reference value (0.738) in extreme obesity (0.756; P