The Phase Angle of the Bioelectrical Impedance Analysis as Predictor of Post-Bariatric Weight Loss Outcome

Bariatric surgery is proven to be the most effective therapy for obesity. However, the targeted weight reduction is not always achieved. Reliable predictors for postoperative success are rare. Also, most available predictors, such as gender and socioeconomic status, cannot be influenced. The aim of the study was to assess the reliability of the phase angle (PhA) as a predictor of weight reduction and body composition after bariatric surgery. One hundred seventy-three patients (127 with Roux-en-Y gastric bypass and 46 with sleeve gastrectomy), treated between January 2004 and December 2012, were included into this prospective trial. Bioelectrical impedance analysis (BIA) was performed before and five times within the first year after the operation. Correlation between excess weight loss (EWL) was calculated using Pearson's correlation coefficient and a receiver operating characteristic (ROC) curve. The average weight loss was significant with a total weight loss of 30.1 %, while the PhA did not show any significant decrease during the first 12 months after surgery. The correlation between the preoperative PhA and the postoperative EWL was significant after 6 weeks and after 6, 9, and 12 months. The ROC curve has an area of 0.7. The best point of the curve is a PhA of 3.9A degrees with a sensitivity of 81 % and a specificity of 54 %. PhA may be a useful predictor of EWL after bariatric surgery, and a PhA of 3.9A degrees was calculated as the most suitable cut-off for a successful operation.