Scientists from the Minnesota Applied Research Center (MARC) investigated whether a whey protein based supplement, high in leucine and bioactive peptides, would enhance weight-loss in those undergoing modest dieting. A total of 106 age and weight matched subjects were assigned to one of a control (CTRL) or whey protein (WP) supplement group. In this 12-week double blind placebo controlled study, subjects consumed an isocaloric diet (with standardized protein consumption). Individual dietary calories were calculated as resting metabolic rate (measured by indirect calorimetry) x 1.3 - 500 calories, such that each subject was in an approximate 500 calorie deficit per day. The volunteers ingested either a placebo or whey protein drink 20 minutes before breakfast and dinner. After 12 weeks the investigators observed that both groups had significant weight loss, with no differences in total weight loss between groups. However, compared to CTRL, the WP subjects maintained more lean mass and, in contrast to the CTRL group, their weight-loss was primarily attributed increased fat loss (confirmed by dual-xray absorptiometry (DEXA).
Frestedt JL, Zenk JL, Kuskowski MA, Ward LS, Bastian ED. A whey-protein supplement increases fat loss and spares lean muscle in obese subjects: a randomized human clinical study. Nutr Metab (Lond). 2008 Mar 27;5:8.