Caloric-restricted weight loss, especially rapid weight loss, results from a decrease in both lean and fat mass (FM). The goal for many is to lose FM while retaining lean body mass (LBM) and muscular performance thus many turn to supplements. Sixteen resistance trained males (24+/- 1.6 years of age) completed a 4 d/wk body building style split resistance training program for eight weeks in conjunction with a pre, peri-, and post-exercise ingestion of whey protein (WHEY) nutritional supplement or carbohydrate (CON) based nutritional supplement. There were no differences in body mass change between the WHEY and CON groups even though both groups lost body mass (p<.05), however WHEY group maintained LBM while the CON group lost (p<.05), and the WHEY group lost FM (p>.05) and the CON group did not, though the change in FM between groups was not different. Both the WHEY and CON (p<.05) groups significantly increased lower body strength.. The WHEY group increased upper body strength (p<.05) while the CON did not change. Both groups (P<.05) increased lower body repetitions to fatigue with the increase greater in the CON group (p<.05). The CON group also increased upper body repetitions (P<.05) while WHEY did not. WHEY group lost body mass, composed of FM while CON also experienced a loss in body mass, but this loss was due to decrease in LBM. Neither group experienced a loss in muscle performance, with the WHEY group tending to show improvement in strength and CON group in endurance. These data indicate WHEY supplementation; compared to CHO supplementation, during a caloric-restricted 'cut' diet can assist in maintaining LBM while allowing for the loss of FM. Copyright (C) 2015 by the National Strength & Conditioning Association.