Background:
The lesser anabolic properties of plant-based compared with animal-based proteins has been attributed to differences in essential amino acid (EAA) content and amino acid composition. This study compares muscle protein synthesis rates following the ingestion of milk protein with the ingestion of corn protein or a blend combining corn and milk protein in vivo, in young males.

Methods:
In a randomized, double blind, parallel-group design, 36 healthy, young men (26±4 y) received a primed continuous infusion of L-[ring-¹³C₆]-phenylalanine and ingested 30 g milk protein (MILK), 30 g corn protein (CORN), or a protein blend of 15 g corn protein plus 15 g milk protein (CORN+MILK) (n=12 per group). Blood and muscle biopsies were collected for 5 hours following protein ingestion to assess post-prandial plasma amino acid profiles and myofibrillar protein synthesis rates. Data were analyzed with 2-way repeated measures ANOVA and independent samples t-test.

Results:
MILK increased plasma EAA concentrations more when compared to CORN (P<0.001). Both milk and corn protein ingestion increased myofibrillar protein synthesis rates (P<0.001), with no differences between treatments (0.053±0.013 vs 0.052±0.013 %/h, respectively; P=0.90). When MILK was compared to CORN+MILK, plasma EAA concentrations increased more in MILK when compared to CORN+MILK (P<0.05). CORN+MILK ingestion also increased myofibrillar protein synthesis rates (P<0.001), with no differences between MILK and CORN+MILK (0.053±0.013 vs 0.052±0.024 %/h, respectively, P=0.99).

Conclusions:
Ingestion of 30 g milk protein, 30 g corn protein, or a blend of 15 g corn plus 15 g milk protein increases muscle protein synthesis rates in healthy, young men. Post-prandial muscle protein synthesis rates following the ingestion of 30 g milk protein do not differ from rates observed after ingesting 30 g corn protein or a blend providing 15 g milk plus 15 g corn protein in young, healthy males.