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

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.

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/m² 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.

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.

%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.