Background: Many military personnel take dietary supplements, presumably to improve their strength and/or endurance, yet there is little to no guidance available for their use. Supplementation with leucine and whey protein has been shown to improve single-bout exercise performance and result in greater physical strength. It has been further suggested that the combination of whey protein with leucine may be more powerful than either supplement alone to increase whole-body net protein balance. Supplementation with protein and branched-chain amino acids such as leucine may also improve cognitive performance, although the clinical evidence is conflicting. Improvements in strength and cognition likely translate directly into increased operational capability for military personnel.

Hypothesis/purpose of study: The purpose of this study was to investigate the ability of 8 weeks of whey-protein and leucine supplementation to enhance physical and cognitive performance and body composition.

Subjects:Thirty-three participants completed the study (30 males, 3 females). The female participants were removed from the report because of the inherently difficult task of comparing macronutrient responses between sexes. The mean age of the remaining male participants was 26.9 years, and 24 of the 30 were United States Air Force (USAF) personnel. Participants must have performed exercise at least 3 times per week for the past 3 months.

Experimental design: Randomized, double-blind

Treatments and protocol:Participants completed a presupplement session consisting of a dual-energy X-ray absorptiometry body-composition scan, a blood draw, and approximately 1 hour of cognitive test-battery training. Presupplement testing included a 1-repetition-maximum (1-RM) bench press and maximum chin-up, push-up, and crunch repetitions completed within 1 minute with a 3-minute break between exercises. After the crunches, participants received a 5-minute rest before beginning a timed 3-mile (4.8 km) run during which they were asked to sprint as fast as possible for the last 40 yd (36.6 m). Participants took a 10- to 15-minute break between physical testing and cognitive testing. Participants were assigned to either the protein group (WPL; n = 18) or the placebo group (P; n = 12) and consumed the protein or placebo daily for 8 weeks. Each packet of the protein treatment contained 112 kcal, including 19.7 g of whey protein and 6.2 g leucine. Placebo packets contained 112 kcal of carbohydrate (type not specified) with no protein. Each day, participants recorded their exercise activity, duration, and intensity. A retrospective analysis of the bench press data categorized participants into 3 groups; those who participated in at least 2 hours of resistance training (RT) per week over and above minimum guidelines (high-RT), those completing 1 to 2 hours/week (medium-RT), and those completing less than 1 hour/week (low-RT). Compliance was measured and a medical screening was performed after 4 weeks, and participants were tested in the exact same fashion as at presupplementation at the end of 8 weeks.