Pea and soy fortified with leucine stimulates muscle protein synthesis comparable to whey in a murine ageing model

Purpose To meet the global dietary protein demands, a trend towards plant-based protein (PBP) sources to replace animal-derived protein is currently ongoing. However, PBPs may not have the same anabolic capacity to stimulate muscle protein synthesis (MPS) as dairy proteins. For vulnerable populations with specific medical needs, it is especially important to validate the anabolic properties of PBPs. In this study, a blend of pea and soy protein isolate, with or without additional leucine, was compared to whey protein isolate on MPS in aged mice. Methods 25-Months aged C57BL/6J-mice received an oral gavage with 70 mg of whey protein isolate (W), PS protein isolate (PS; ratio 51:49), PS fortified with 19% leucine (PS + L), or 0.5mL water (F). Mice were subcutaneously injected with puromycin (0.04 mu mol/g body weight, t = 30 min) and sacrificed 60 min thereafter. Left m. tibialis anterior (TA) was used to analyse MPS by the SUnSET method and mTOR signal transduction proteins. Amino acid concentrations were determined in plasma and right TA. Dried blood spots (DBS) were analysed for postprandial dynamics of amino acids at 10-20-45-60-min. Results MPS was significantly increased by W and PS + L (p < 0.003), however not by PS. Pathway protein 4EBP1 showed significant increases with W, PS and PS + L to F (p < 0.0002). W and PS + L increased plasma and muscle free leucine equally, which was confirmed by DBS. Conclusion A PS blend fortified with leucine stimulates MPS comparable to whey protein in this acute murine ageing model. Leucine appears to be the main driver for the anabolic responses observed.