Coingestion of Carbohydrate and Protein Hydrolysate Stimulates Muscle Protein Synthesis during Exercise in Young Men, with No Further Increase during Subsequent Overnight Recovery
We investigated the effect of carbohydrate and protein hydrolysate ingestion on whole-body and muscle protein synthesis during a combined endurance and resistance exercise session and subsequent overnight recovery. Twenty healthy men were studied in the evening after consuming a standardized diet throughout the day. Subjects participated in a 2-h exercise session during which beverages containing both carbohydrate (0.15 g·kg–1·h–1) and a protein hydrolysate (0.15 g·kg–1·h–1) (C+P, n = 10) or water only (W, n = 10) were ingested. Participants consumed 2 additional beverages during early recovery and remained overnight at the hospital. Continuous i.v. infusions with L-[ring-13C6]-phenylalanine and L-[ring-2H2]-tyrosine were applied and blood and muscle samples were collected to assess whole-body and muscle protein synthesis rates. During exercise, whole-body and muscle protein synthesis rates increased by 29 and 48% with protein and carbohydrate coingestion (P < 0.05). Fractional synthetic rates during exercise were 0.083 ± 0.011%/h in the C+P group and 0.056 ± 0.003%/h in the W group, (P < 0.05). During subsequent overnight recovery, whole-body protein synthesis was 19% greater in the C+P group than in the W group (P < 0.05). However, mean muscle protein synthesis rates during 9 h of overnight recovery did not differ between groups and were 0.056 ± 0.004%/h in the C+P group and 0.057 ± 0.004%/h in the W group (P = 0.89). We conclude that, even in a fed state, protein and carbohydrate supplementation stimulates muscle protein synthesis during exercise. Ingestion of protein with carbohydrate during and immediately after exercise improves whole-body protein synthesis but does not further augment muscle protein synthesis rates during 9 h of subsequent overnight recovery.
Whey Protein Ingestion Enhances Postprandial Anabolism during Short-Term Bed Rest in Young Men
We tested the relative ability of rapidly digested whey and slowly digested casein to stimulate net whole-body protein synthesis during prolonged physical inactivity. We studied 8 young male volunteers after they consumed isonitrogenous casein or whey mixed meals on d 12 or d 14 of experimental bed rest. Rates of phenylalanine hydroxylation were measured by primed-constant oral administration of L[2-2H2]tyrosine and L[ring-2H5]phenylalanine for 3 h in the postabsorptive state and 6 h after an isonitrogenous bolus meal containing sucrose (0.27 g/kg) and casein or whey (0.40 g/kg). Net protein synthesis in the fed state was calculated during the first 6 h postmeal as the difference between phenylalanine hydroxylation and phenylalanine content in the ingested casein or whey. In the fed state, the integrated changes in phenylalanine hydroxylation were lower (P < 0.05) after whey (–2 ± 8 µmol·kg–1·6 h–1) than after casein ingestion (34 ± 7 µmol·kg–1·6 h–1). During bed rest, net postprandial protein synthesis was greater (P < 0.05) after whey (96 ± 8 µmol phenylalanine·kg–1·6 h–1) than after casein ingestion (82 ± 7 µmol phenylalanine·kg–1·6 h–1). The rapidly digested whey protein was more efficient than the slowly digested casein in increasing postprandial net protein synthesis during short-term bed rest.