Carbohydrate co‐ingestion with protein delays dietary protein digestion and absorption but does not modulate postprandial muscle protein accretion

Abstract

We determined the impact of carbohydrate co‐ingestion with protein on dietary protein digestion and absorption kinetics and postprandial muscle protein accretion in healthy men. Twenty‐four young (age: 21±1 y, BMI: 21.8±0.5 kg/m2) and 24 older (age: 75±1 y, BMI: 25.4±0.6 kg/m2) men received a primed continuous L‐[ring‐2H5]‐phenylalanine infusion and ingested 20 g L‐[1‐13C]‐ phenylalanine‐labeled protein with (PRO+CHO) or without (PRO) 60 g carbohydrate. Biopsies were collected from the vastus lateralis. Carbohydrate co‐ingestion delayed the rise in exogenous phenylalanine appearance rate (P<0.05). Dietary protein‐derived phenylalanine availability over the postprandial period was lower in the old (60±2%) when compared with the young (72±2%; P<0.05), with no differences between the PRO and PRO+CHO condition (P=0.42). Carbohydrate co‐ingestion did not modulate postprandial muscle protein synthesis rates (0.035±0.003 vs 0.043±0.004 and 0.033±0.002 vs 0.035±0.003 %/h following PRO vs PRO+CHO in the young and old, respectively). In accordance, no differences in muscle protein‐bound L‐[1‐13C]‐phenylalanine enrichments were observed between groups (0.020±0.003 vs 0.018±0.003 and 0.017±0.003 vs 0.022±0.004 MPE following PRO vs PRO+CHO in the young and old, respectively). We conclude that carbohydrate co‐ingestion does not modulate postprandial muscle protein accretion in young or older men.