The Effects of Protein Type and Added Leucine on Myofibrillar Protein Synthesis Following Concurrent Exercise

Abstract

Protein ingestion increases skeletal muscle protein synthesis (MPS) rates. The effect of protein on MPS rates is enhanced by prior exercise. However, the effect of different types of protein on MPS is unclear and has not been evaluated following concurrent exercise. PURPOSE: The objective of this study was to determine the capacity of total milk protein (MILK), whey (WHEY), micellar casein (CASEIN), and soy protein, without (SOY) and with additional leucine (SOY+LEU) to support postprandial myofibrillar protein synthesis (MyoPS) following concurrent exercise. METHODS: 72 young recreationally active males participated in this parallel group, double-blind, randomized controlled trial consisting of two arms. In arm #1, 48 subjects (23±0.3 y) ingested 45 g of carbohydrate with either 0 g protein (CHO), or 20 g MILK, WHEY, or CASEIN protein. In arm #2, 36 subjects (23±0.5 y) ingested 45 g of carbohydrate with 20 g WHEY, SOY, or SOY+LEU. A primed continuous infusion of L-[ring-13C ]-phenylalanine with blood and muscle biopsies was applied to evaluate postprandial MyoPS over 360 minutes after exercise. RESULTS: In arm #1, MyoPS did not differ between treatments (P=0.12) during the postprandial period after exercise (FSR: CHO=0.051±0.003; MILK=0.061±0.003; WHEY=0.056±0.002; CASEIN=0.062±0.005 %/h). When MILK, WHEY, and CASEIN were collapsed into a single group (PROTEIN), protein-carbohydrate co-ingestion resulted in greater MyoPS rates than carbohydrate alone (FSR: PROTEIN=0.060±0.002; CHO=0.051±0.003 %/h; P=0.042). In arm #2 MyoPS did not differ between treatments (P=0.85) after exercise (FSR: WHEY=0.056±0.002; SOY=0.056±0.004; SOY+LEU=0.058±0.004 %/h). CONCLUSION: Total milk protein, whey, and micellar casein (arm #1) do not differ in their capacity to support postprandial MyoPS rates when co-ingested with carbohydrate following concurrent exercise in young males. Similarly, whey and soy protein, irrespective of leucine enrichment of soy (arm #2), do not differ in their capacity to support postprandial MyoPS after concurrent exercise. Co-ingestion of protein with carbohydrate results in greater postprandial MyoPS rates than carbohydrate alone, and may therefore represent a nutritional strategy to support skeletal muscle remodeling following concurrent exercise.