Changes in the Phase Angle after Bariatric Surgery: A Meta-Analysis

Background: Phase angle (PhA), a parameter derived from bioelectrical impedance analysis, is associated with lean mass and muscle mass. Bariatric surgery can result in significant changes in body composition. The objective of this meta-analysis was to determine the impact of bariatric surgery on PhA. Methods: A systematic review and meta-analysis were conducted following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, including studies up to January 2025 from five databases. Eligible studies assessed PhA alterations before and after bariatric surgery. Results: Thirteen studies with a total of 825 patients were included. Significant PhA reduction was observed following bariatric surgery (weighted mean difference: −0.922; 95% confidence interval [CI]: −1.063, −0.781; p < 0.001). Random-effects meta-regression showed a significant association between ΔPhA and ΔBMI (slope: 0.072; 95% CI: 0.033, 0.112; p = 0.0003) and Δfat-free mass (slope: 0.080; 95% CI: 0.052, 0.107; p < 0.001), but no association with Δfat mass. PhA values decreased significantly with following bariatric surgery, but there were no differences between Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG). Conclusions: This meta-analysis offers evidence regarding the impact of bariatric surgery on bioimpedance parameters, including PhA, in individuals with obesity.