|Abstract:||Skeletal muscle mass and quality, which is determined by day-to-day changes in muscle protein synthesis (MPS) and muscle protein breakdown rates (MPB), are important determinants of physical performance and metabolic health across all age groups. As such, identifying nutritional and exercise strategies that more robustly stimulate MPS and inhibit MPB after each meal are important to optimize skeletal muscle mass and health. The leucine content of a meal is believed to be an important anabolic characteristic of a meal. Specifically, leucine is a potent amino acid that serves both as an anabolic signaling molecule and substrate to potentiate MPS. Beyond single amino acids, food proteins also contain dipeptides. Little is known, however, about the anabolic and catabolic effects of dipeptides, whose uptake rates have been shown to be faster than corresponding free amino acid. As such, uncovering how dipeptides impact muscle protein turnover is warranted to develop more anabolic nutritional strategies. The study within this thesis aimed to determine the effect of dipeptide (i.e., leucine-leucine; DILEU) ingestion on changes in MPS and MPB rates when compared to leucine (LEU) in single form. Ten young men completed a double-blind, randomized crossover study. Participants were randomized to ingest either 2.00g of LEU or 2.47g of DILEU mixed in 150mL of water. After an overnight fast, participants received a primed constant infusion of L-[ring-13C6]- and [15N]-phenylalanine to measure MPS and MPB rates. Plasma insulin, glucose, leucine and dileucine concentrations were also measured. Results from this study demonstrated that DILEU stimulates MPS to a greater extent than LEU. There was no difference in MPB rates between conditions. Plasma insulin, glucose, leucine, and dileucine concentrations did not differ between conditions. These data suggest that DILEU may be used in food fortification or clinical feeding formulas to enhance the anabolic properties of meals.