Carbohydrate co-ingestion with protein does not further augment post-prandial muscle protein accretion in older men

Abstract

BackgroundA blunted muscle protein synthetic response to protein ingestion may contribute to the age related loss of muscle tissue. We hypothesized that the greater endogenous insulin release following co-ingestion of carbohydrate facilitates post-prandial muscle protein accretion after ingesting a meal-like bolus of protein in older males.MethodsTwenty-four healthy older men (75±1 y) were randomly assigned to ingest 20 g intrinsically L-[1-13C] phenylalanine-labeled casein protein with (PRO-CHO) or without (PRO) 40 g carbohydrate. Ingestion of specifically produced intrinsically L-[1-13C] phenylalanine labeled protein allowed us to assess post-prandial incorporation of dietary protein derived amino acids into muscle protein. Blood samples were collected at regular intervals, with muscle biopsies being obtained prior to and 2 and 6 h after protein ingestion.ResultsPlasma glucose and insulin concentrations showed a greater increase in PRO-CHO compared with PRO (P<0.001). Muscle protein-bound L-[1-13C] phenylalanine enrichments tended to increase to a greater extent in PRO-CHO compared with PRO during the first 2 h after protein ingestion (0.0072±0.0013 vs 0.0046±0.010 MPE, respectively; P=0.13). However, 6 h after protein ingestion, differences in muscle protein-bound L-[1-13C] phenylalanine enrichments were no longer observed between experiments (0.0213±0.0024 vs 0.0185±0.0010 MPE, respectively; P=0.30).ConclusionsThis study shows that carbohydrate ingestion may accelerate, but does not further augment post-prandial incorporation of dietary protein derived amino acids into muscle protein in healthy elderly men.

Protein type and caloric density of protein supplements modulate postprandial amino acid profile through changes in gastrointestinal behaviour: A randomized trial

“…So far, it has only been suggested that, by comparing between studies, the difference in digestion rate for whey versus casein in a mixed meal is less pronounced than when the proteins are given without added calories [16,19]. In line with our observations, the co-ingestion of carbohydrates with casein protein lowered plasma AA levels in older adults [39], and also delayed digestion and absorption kinetics using intrinsically labelled casein [26]. Only one study in young adults showed lower peak plasma levels of leucine, branched chain amino acids (BCAA) and EAA when whey protein was co-ingested with carbohydrates [40].…”

Hydrolyzed casein and whey protein meals comparably stimulate net whole-body protein synthesis in COPD patients with nutritional depletion without an additional effect of leucine co-ingestion

“…Some studies that found an anabolic effect of leucine did not add carbohydrates to the protein/amino acid meals (9, 13, 29). Recent research show that the effects of leucine are almost comparable to the effects of adding carbohydrates (29, 30), while it is unknown whether adding both leucine and carbohydrates is of additional benefit. We conclude based on our study that this is not the case and that protein anabolism is optimally stimulated when you use a high quality hydrolyzed milk protein meal with added carbohydrates.…”

Ingestion of Casein in a Milk Matrix Modulates Dietary Protein Digestion and Absorption Kinetics but Does Not Modulate Postprandial Muscle Protein Synthesis in Older Men

“…As a consequence, there has been an increasing interest in identifying the characteristics that determine the postprandial rise in muscle protein synthesis rates. This work has addressed the impact of the type (4-7) and dose (5,(8)(9)(10)(11)(12)(13)(14) of protein, as well as the timing (15) and the matrix (16,17) in which the protein is ingested. More insight into the characteristics that modulate postprandial muscle protein synthesis will allow us to define more anabolic food products and may support the development of more effective dietary strategies to prevent and/or treat muscle loss with aging.…”