The Impact of Ingesting a Whole-food Animal-based Versus Plant-based Protein Rich Meal on the Muscle Protein Synthetic Response in Healthy Older Men and Women

Food intake stimulates muscle protein synthesis rates. The anabolic response to feeding forms a key factor in regulating muscle mass maintenance. Impairments in the sensitivity of skeletal muscle tissue to respond to the anabolic properties of protein feeding have been reported in numerous settings where muscle mass is being lost, such as aging, disuse, chronic metabolic disease, and various clinical conditions where muscle wasting is apparent.

The capacity of a dietary protein to stimulate post-prandial muscle protein accretion depends on the digestion and absorption kinetics of that protein as well as its amino acid composition. A more rapid rise in circulating essential amino acids (EAAs), with leucine in particular, drives the post-prandial rise in muscle protein synthesis rates. It has been suggested that plant and animal based protein sources do not have the same anabolic properties due to differences digestibility and essential amino acid composition. However, so far, nearly all studies evaluating the muscle protein synthetic response to food ingestion have applied a reductionist approach and have determined the muscle protein synthetic response to the ingestion of isolated protein sources (e.g., whey, casein, soy) with or without other isolated meal components (e.g., carbohydrates, fats). This work suggests that the ingestion of isolated animal-based proteins stimulates a superior muscle protein synthetic response when compared to the ingestion of isolated plant-based proteins. However, protein isolates never constitute the main protein portion of a meal. Perhaps more importantly, it is often neglected that the anabolic properties of protein isolates do not necessarily reflect the anabolic response to the ingestion of the whole-foods from which those are derived. This discrepancy is due to the presence or absence of other nutritional components within whole-food matrices. In particular, plant-derived protein sources contain anti-nutritional factors that impair protein digestion and amino acid absorption and, as such, compromise the post-prandial rise in muscle protein synthesis rates.

Therefore, this project will compare the impact of the ingestion of a whole-food meal with beef as the primary source of protein, with the ingestion of a whole food meal ingestion with only plant derived protein sources, on the muscle protein synthetic response in healthy older men and women.