Myofibrillar and Mitochondrial Protein Synthesis Rates Do Not Differ in Young Men Following the Ingestion of Carbohydrate with Milk Protein, Whey, or Micellar Casein after Concurrent Resistance- and Endurance-Type Exercise

Protein ingestion during recovery from resistance-type exercise increases postexercise muscle protein synthesis rates. Whey protein has been reported to have greater anabolic properties than soy protein, an effect which may be attributed to the higher leucine content of whey. Objective: The objective of this study was to compare postprandial myofibrillar (MyoPS) and mitochondrial (MitoPS) protein synthesis rates after ingestion of carbohydrate with whey, soy, or soy protein enriched with free leucine (to match the leucine content of whey) during recovery from a single bout of concurrent resistance- and endurance-type exercise in young healthy men. Methods: In a randomized, double-blind, parallel-group design, 36 healthy young recreationally active men (mean SEM age: 23 0.4 y) received a primed continuous infusion of L-[ring-13C6]-phenylalanine and L-[ring-3,5-2H2]-tyrosine and ingested 45 g carbohydrate with 20 g protein from whey (WHEY), soy (SOY), or leucine-enriched soy (SOY + LEU) after concurrent resistance- and endurance-type exercise. Blood and muscle biopsies were collected over a 360 min postexercise recovery period to assess MyoPS and MitoPS rates, and associated signaling through the mammalian target of rapamycin complex 1 (mTORC1). Results: Postprandial peak plasma leucine concentrations were significantly higher in WHEY (mean SEM: 322 10 Umol/L) and SOY + LEU (328 14 Umol/L) compared with SOY (216 6 Umol/L) (P < 0.05). Despite the apparent differences in plasma leucinemia,MyoPS (WHEY: 0.054 0.002; SOY: 0.053 0.004; SOY + LEU: 0.056 0.004%h-1; = 0.83), and MitoPS (WHEY: 0.061 0.004; SOY: 0.061 0.006; SOY + LEU: 0.063 0.004%h-1; P = 0.96) rates over the entire 360 min recovery period did not differ between treatments. Similarly, signaling through mTORC1Ser2448, p70S6kThr389, 4E-BP1Thr37/46, and rpS6Ser235/236 was similar between treatments. Conclusion: Postexercise MyoPS and MitoPS rates do not differ after co-ingestion of carbohydrate with 20 g protein from whey, soy, or leucine-enriched soy protein during 360 min of recovery from concurrent resistance- and endurancetype exercise in young, recreationally active men. This trial was registered at Nederlands Trial Register as NTR5098. J Nutr 2019;149:210-220.