Protein Matrix Impacts Essential Amino Acid Response To Feeding

Abstract

It is well established that muscle protein turnover is highly response to increases in plasma essential amino acids (EAA). Digestion and amino acid absorption kinetics appear to strongly modulate post-prandial muscle protein synthesis. Despite this relationship, little is known about the effects of the protein matrix on plasma EAA appearance. PURPOSE: To assess if protein matrix alters plasma EAA pharmacokinetics (PK). METHODS: 24 healthy young individuals (24.7 ± 4.7y; BMI = 24.6 ± 3.2 kg/m2) completed this study. Participants consumed one of the following protein matrices: whey protein isolate (W; 6.8 g of EAA), beef sirloin (B; 7.0 g of EAA), or free form EAA enriched W (FW; 5.6 g of EAA). Blood samples were collected before and four hours following the ingestion of W, B, and FW. Plasma EAA were analyzed via LC-MS/MS. Standard pK values were calculated: area under the curve above baseline (AUCi), max EAA concentration (Cmax), EAA concentration change from baseline to EAACmax (ΔEAA), rate to Cmax, and time to Cmax. To examine group differences in EAA pK a one-way analysis of variance with Tukey post hoc test was performed with significance accepted at P ≤ 0.05. RESULTS: Significant group differences were noted for all measured pK (p ≤ 0.005). Post hoc comparisons indicated AUCi was significantly lower in W (50705.6 ± 13483.3 μmol/L/min) as compared to FW (84793.8 ± 15989.7 μmol/L/min; p = 0.004) and B (77084.6 ± 25076.0 μmol/L/min; p = 0.028). Cmax, ΔEAA, and rate to Cmax was significantly higher in FW (Cmax = 1,920 ± 242.6 μmol/L; ΔEAA = 1012.4 ± 200.8 μmol/L; rate to Cmax = 30.1 ± 13.0 μmol/L/min) as compared to W (Cmax = 1343.1 ± 144.4 μmol/L, p ≤ 0.001; ΔEAA = 556.9 ± 160.1 μmol/L, p ≤ 0.001; rate to Cmax = 13.6 ± 7.6 μmol/L/min, p = 0.003) and B (Cmax = 1339.9 ± 213.5 μmol/L, p ≤ 0.001; ΔEAA = 543.8 ± 164.2 μmol/L, p ≤ 0.001; rate to Cmax = 4.9 ± 2.7 μmol/L/min, p ≤ 0.001). Lastly, the time to Cmax was slowest in B (135.0 ± 62.1 mins) as compared to W (47.5 ± 14.9 mins; p ≤ 0.001) and FW (36.3 ± 7.4 mins; p ≤ 0.001). CONCLUSION: Despite similar EAA content, pharmacokinetics were significantly different between treatments. Despite the lowest EAA content, FW resulted in the greatest plasma EAA availability and quickest time to peak. These results indicate that protein/amino acid digestion is a primary determinant of plasma EAA availability.