Ingestion of 20 g of a plant-derived protein blend with and without added leucine or whey protein does not increase muscle protein synthesis rates in older males.

BACKGROUND: Sufficient high-quality protein intake is required to prevent sarcopenia in older adults. Plant-based proteins have been reported to have lesser anabolic properties when compared to animal-based proteins. Whether the lower quality of plant-based protein can be improved, thereby resulting in an anabolic response non-inferior to an equivalent amount of animal-based protein, remains to be established in older adults. OBJECTIVE: To compare post-prandial muscle protein synthesis rates following ingestion of a single bolus of a soy-pea protein blend, with a soy-pea protein blend fortified with free leucine, or whey protein in older males. METHODS: In this randomized, double-blind, parallel-group design, 45 healthy older males (aged 69±5 y, BMI 26.2±3.2 kg∙m-2) were selected to ingest a 20g protein blend combining 12g soy plus 8g pea protein (PLANT), 20g of the soy-pea protein blend fortified with 2g leucine (PLANT+LEU), or 20g whey protein (WHEY). Primed continuous L-[ring-13C6]-phenylalanine infusions were applied, with blood and muscle sampling up to 4 h after protein ingestion to assess plasma amino acid profiles and muscle protein synthesis rates. RESULTS: WHEY increased plasma essential amino acid concentrations more than PLANT and PLANT+LEU over the 4 h post-prandial period (iAUC:135±20 vs 99±21 vs 105±21 mmol∙240 min∙L-1, respectively; P<0.001). Plasma peak leucine concentrations were higher following PLANT+LEU ingestion compared to PLANT and WHEY (567±74 vs 310±49 vs 471±74 μmol∙L-1, respectively; P<0.001). Post-prandial muscle protein synthesis rates averaged 0.034±0.010, 0.035±0.012, and 0.034±0.010 %∙h-1 following PLANT, PLANT+LEU, and WHEY ingestion, respectively (treatment P=0.828), and were not increased when compared to post-absorptive values. CONCLUSION: Ingestion of 20 g protein alone, independent of its quality, is not enough to increase muscle protein synthesis rates in older males. More work is needed to define the preferred combination of both protein quality and quantity to stimulate muscle protein synthesis in an older population. CLINICAL TRIAL REGISTRY NUMBER: NCT05711095 (clinicaltrials.gov).