Myofibrillar and Mitochondrial Protein Synthesis Rates Do Not Differ in Young Men Following the Ingestion of Carbohydrate with Whey, Soy, or Leucine-Enriched Soy Protein after Concurrent Resistance- and Endurance-Type Exercise.
Level 2 - randomized trial
Randomized, double-blind, parallel-group clinical trial
PubMed 30698812 · doi:10.1093/jn/nxy251
What was done
Thirty-six healthy, recreationally active young men (mean age: 23 ± 0.4 years) participated in a randomized, double-blind, parallel-group study. Following a single bout of concurrent resistance- and endurance-type exercise, participants received a primed continuous infusion of stable amino acid tracers (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 soy enriched with free leucine (SOY + LEU). Blood and muscle biopsy samples were obtained across a 360-minute post-exercise recovery period to measure myofibrillar protein synthesis (MyoPS), mitochondrial protein synthesis (MitoPS), and mTORC1 signaling pathways.
What was found
Peak postprandial plasma leucine concentrations were significantly higher in WHEY (322 ± 10 µmol/L) and SOY + LEU (328 ± 14 µmol/L) than in SOY (216 ± 6 µmol/L; P < 0.05). Despite these differences in leucinemia, MyoPS rates over the 360-minute period did not differ significantly between treatments (WHEY: 0.054 ± 0.002 %·h-1; SOY: 0.053 ± 0.004 %·h-1; SOY + LEU: 0.056 ± 0.004 %·h-1; P = 0.83). Similarly, MitoPS rates showed no significant differences (WHEY: 0.061 ± 0.004 %·h-1; SOY: 0.061 ± 0.006 %·h-1; SOY + LEU: 0.063 ± 0.004 %·h-1; P = 0.96). Phosphorylation of mTORC1Ser2448, p70S6kThr389, 4E-BP1Thr37/46, and rpS6Ser235/236 was also comparable among all groups.
Why it matters
This study shows that soy protein stimulates both myofibrillar and mitochondrial protein synthesis as effectively as whey or leucine-enriched soy when co-ingested with carbohydrate after concurrent exercise. It suggests that leucine fortification of soy protein may be unnecessary for acute post-exercise muscle protein synthesis under these conditions.
Limits
The study was limited by a small sample size (n = 36 total, 12 per group) and included only young, recreationally active men, preventing generalization to females, older populations, or elite athletes. The design evaluated an acute 360-minute recovery period after a single exercise session, which does not directly reflect long-term training adaptations such as muscle hypertrophy or mitochondrial biogenesis. In addition, all protein sources were co-ingested with carbohydrate, which may have masked subtle differences between protein types.
Cited by
- context Combining leucine-rich essential amino acids with whey protein powder makes the whey protein powder more effective at stimulating protein synthesis.