The Relationship Between BMI, Body Composition, and Fat Mass Distribution in Rou-en-Y Gastric Bypass Patients

Background Type 2 diabetes mellitus (T2DM) with central obesity is a common clinical presentation in Chinese patients. Body mass index (BMI) is a criterion determining central obesity that, when combined with dual-energy X-ray absorptiometry (DXA), accurately reflects body composition and fat mass distribution. The utility of DXA-derived measures in the evaluation of metabolic surgery still needs to be investigated. Methods In this cohort study, 78 Chinese patients with central obesity (WC ≥ 90 cm for males, WC ≥ 85 cm for females) or BMI above 27.5 kg/m 2 underwent gastric bypass between October 2010 and October 2012. The patients were followed for 12 months. Preoperative, perioperative, and postoperative metabolic parameters and DXA results were prospectively collected and analyzed. Results A total of 57 of 78 cases (73.1%) were diagnosed with central obesity. There was a significant decrease in BMI, WC, and WHR at each point in time ( P < 0.05), with fasting plasma glucose (FPG), fasting insulin secretion (FINS), and the homeostasis model assessment of insulin resistance index (HOMA-IR) also significantly improved. Body fat mass percentage (%BF) results showed significant decreases in different regions. %BF regions, except for trunk region %BF, were significantly correlated with BMI and WC ( P < 0.01). Pearson correlation coefficients of 0.562 and 0.577 were evident between BMI and total %BF, and android %BF and WC, respectively. Linear regression analysis was conducted to assess the linear relationship between BMI and %BF, and android %BF, WC, and WHR; linear formulas were derived. Conclusions %BF is a more significant predictor of obesity, with BMI significantly underestimating visceral adipose tissue (VAT). In addition to BMI, total %BF and android %BF have clinical utility as indicators for metabolic surgery evaluation as well as patient selection.