Branched-Chain Amino Acid Fortification Does Not Restore Muscle Protein Synthesis Rates following Ingestion of Lower- Compared with Higher-Dose Mycoprotein

Abstract

We have shown that ingesting a large bolus (70g) of the fungal-derived, whole food mycoprotein robustly stimulates muscle protein synthesis (MPS) rates. The aim of this study was to determine if a lower dose (35g) of mycoprotein enriched with branched-chain amino acids (BCAAs) stimulates MPS to the same extent as 70g of mycoprotein in resistance-trained young men. Nineteen men [aged 22±1y, BMI (kg/m2): 25±1] took part in a randomized, double-blind, parallel-group study. Participants received primed, continuous infusions of l-[ring-2H5]phenylalanine and ingested either 70g mycoprotein (31.5g protein; MYCO; n=10) or 35g BCAA-enriched mycoprotein (18.7g protein: matched on BCAA content; ENR; n=9) following a bout of unilateral resistance exercise. Blood and bilateral quadriceps muscle samples were obtained before exercise and protein ingestion and during a 4-h postprandial period to assess MPS in rested and exercised muscle. Two- and 3-factor ANOVAs were used to detect differences in plasma amino acid kinetics and mixed muscle fractional synthetic rates, respectively. Postprandial plasma BCAA concentrations increased more rapidly and to a larger degree in ENR compared with MYCO. MPS increased with protein ingestion (P≤0.05) but to a greater extent following MYCO (from 0.025%±0.006% to 0.057%±0.004% · h-1 in rested muscle, and from 0.024%±0.007% to 0.072%±0.005% · h-1 in exercised muscle; P<0.0001) compared with ENR (from 0.031%±0.003% to 0.043%±0.005% · h-1 in rested muscle, and 0.027%±0.005% to 0.052%±0.005% · h-1in exercised muscle; P<0.01) ingestion. Postprandial MPS rates were greater in MYCO compared with ENR (P<0.01). The ingestion of lower-dose BCAA-enriched mycoprotein stimulates resting and postexercise MPS rates, but to a lesser extent compared with the ingestion of a BCAA-matched 70-g mycoprotein bolus in healthy young men. This trial was registered at clinicaltrials.gov as 660065600.