The Effect of Leucine-Enriched β-Lactoglobulin Versus an Isonitrogenous Whey Protein Isolate on Skeletal Muscle Protein Anabolism in Young Healthy Males

Background: β-lactoglobulin (BLG) is a protein found within whey protein (WP) that is rich in essential amino acids, most notably, leucine (LEU). LEU is considered the most potent EAA in the postprandial stimulation of muscle protein synthesis (MPS), such that suboptimal protein/essential amino acid (EAA) doses containing higher LEU content elicit muscle anabolism comparable to larger protein doses. Our objective was to test the effects of naturally LEU-rich BLG (~10 g protein) versus isonitrogenous whey protein isolate (WPI, ~10 g) on MPS. Methods: Ten healthy young men (26 ± 2 y; 179 ± 2 cm; 81 ± 3 kg) received BLG (1.57 g LEU) or WPI (1.02 g LEU) in a randomised double-blind cross-over fashion. A primed constant intravenous infusion of 1,2 13C2 LEU was used to determine MPS (isotope ratio mass spectrometry) at baseline and in response to feeding (FED) and feeding-plus-exercise (FED-EX; 6 × 8 unilateral leg extensions; 75% 1-RM). Plasma insulin and EAA’s were quantified. Results: Plasma EAA, branched-chain amino acid (BCAA), and LEU concentrations increased rapidly following both protein supplements but exhibited a significantly greater EAA/BCAA/leucinemia following BLG (p < 0.05 for all). MPS increased significantly in both FED (~52%) and FED-EX (~58%) states, with no significant differences between supplements. Conclusions: Both BLG and WPI effectively stimulated MPS doses in young healthy males, with BLG offering an advantage in EAA/BCAA/LEU bioavailability. It follows that future research should explore the potential of BLG in populations exhibiting anabolic resistance and exercise anabolism deficiency, such as older adults as well as frail and clinical populations, to assess its utility in preserving muscle mass under conditions of suboptimal protein intake.