It is known that dieting (restricted energy intake) without resistance training leads to a reduced metabolic rate, and the loss of both fat and muscle mass. When exercise is not included in a period of restricted energy intake, the degree to which muscle mass is lost is highly dependent upon protein consumption. Whey protein is a high quality protein isolated from milk and is known to stimulate new protein synthesis for all proteins in your body. Previous research has established that the consumption of whey protein has been correlated with retaining muscle mass while stimulating fat loss. However, the mechanisms behind these findings is still unknown. The purpose of this study is to establish a mechanistic underpinning to the efficacy of whey protein versus soy protein and a carbohydrate control (maltodextrin), in promoting fat mass loss and lean mass retention during a period of short-term controlled dietary energy deficit (-750 kcalories/day).