Whey Protein Supplementation Enhances Body Fat and Weight Loss in Women Long After Bariatric Surgery: a Randomized Controlled Trial

Background The ideal nutritional approach for weight regain after bariatric surgery remains unclear. Objective The objective of this study is to assess the effect of whey protein supplementation on weight loss and body composition of women who regained weight 24 or more months after bariatric surgery. Methods This is a 16-week open-label, parallel-group, randomized controlled trial of women who regained at least 5 % of their lowest postoperative weight after a Roux-en-Y gastric bypass (RYGB). A total of 34 participants were treated with hypocaloric diet and randomized (1:1) to receive or not supplementation with whey protein, 0.5 g/kg of the ideal body weight. The primary outcomes were changes in body weight, fat free mass (FFM), and fat mass (FM), evaluated by tetrapolar bioelectrical impedance analysis (BIA). Secondary outcomes included resting energy expenditure, blood glucose, lipids, adiponectin, interleukin 6 (IL-6), and cholecystokinin levels. Statistical analyses included generalized estimating equations adjusted for age and physical activity. Results Fifteen patients in each group were evaluated: mean age was 45 ± 11 years, body mass index (BMI) was 35.7 ± 5.2 kg/m 2 , and time since surgery was 69 ± 23 months. Protein intake during follow-up increased by approximately 75 % in the intervention group ( p = 0.01). The intervention group presented more body weight loss (1.86 kg, p = 0.017), accounted for FM loss (2.78, p = 0.021) and no change in FFM, as compared to controls (gain of 0.42 kg of body weight and 0.6 kg of FM). No differences in secondary outcomes were observed between groups. Conclusions Whey protein supplementation promoted body weight and FM loss in women with long-term weight regain following RYGB.