A whey-protein supplement increases fat loss and spares lean muscle in obese subjects: a randomized human clinical study

Background: This study evaluated a specialized whey fraction ( Prolibra (TM), high in leucine, bioactive peptides and milk calcium) for use as a dietary supplement to enhance weight loss. Methods: This was a randomized, double-blind, parallel-arm, 12-week study. Caloric intake was reduced 500 calories per day. Subjects consumed Prolibra or an isocaloric ready-to-mix beverage 20 minutes before breakfast and 20 minutes before dinner. Body fat and lean muscle tissue were measured by dual-energy x-ray absorptiometry ( DEXA). Body weight and anthropometric measurements were recorded every 4 weeks. Blood samples were taken at the beginning and end of the study. Statistical analyses were performed on all subjects that completed ( completer analysis) and all subjects that lost at least 2.25 kg of body weight ( responder analysis). Within group significance was determined at P < 0.05 using a two-tailed paired t-test and between group significance was determined using one way analysis of covariance with baseline data as a covariate. Results: Both groups lost a significant amount of weight and the Prolibra group tended to lose more weight than the control group; however the amount of weight loss was not significantly different between groups after 12 weeks. Prolibra subjects lost significantly more body fat compared to control subjects for both the completer ( 2.81 vs. 1.62 kg P = 0.03) and responder ( 3.63 vs. 2.11 kg, P = 0.01) groups. Prolibra subjects lost significantly less lean muscle mass in the responder group ( 1.07 vs. 2.41 kg, P = 0.02). The ratio of fat to lean loss ( kg fat lost/ kg lean lost) was much larger for Prolibra subjects for both completer ( 3.75 vs. 1.05) and responder ( 3.39 vs. 0.88) groups. Conclusion: Subjects in both the control and treatment group lost a significant amount of weight with a 500 calorie reduced diet. Subjects taking Prolibra lost significantly more body fat and showed a greater preservation of lean muscle compared to subjects consuming the control beverage. Because subjects taking Prolibra lost 6.1% of their body fat mass, and because a 5% reduction of body fat mass has been shown to reduce the risk of obesity related disease, the results have practical significance.