Whey protein may not only be good for
building muscle but losing fat as well. The high leucine content (50-75% more
than other common food proteins) of whey proteins coupled with fast absorption
makes whey protein an ideal protein supplement during weight loss. High leucine
has recently been showed to reduce appetite center signaling pathways in the
brain.  High protein diets have a
nutrient portioning effects on the body; increasing lean muscle mass while
reducing bodyfat.  This study evaluated a
specialized whey fraction (ProlibraTM, high in leucine, bioactive peptides and
milk calcium) for use as a dietary supplement to enhance weight loss. 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.  At the end of 12 weeks, the calorie
comparison between the whey protein group and the control group were similar
but body composition changed more in the whey protein group.  Weight loss was consistently higher in the
Prolibra subjects and weight loss primarily was primarily the result of losing
body fat. The Prolibra subjects lost significantly less lean muscle mass
compared to control subjects.  The
Proliba group also had a reduction in cholesterol.  Prolibra appears to preserve lean muscle and
may partition the weight loss predominantly towards fat at a lower protein
dose, 20 grams per day.  Consuming whey
protein may enhance fat loss through nutrient portioning actions.  

- 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(1):8