Dietary Protein & Muscle Building in Younger Adults

Due to a limited range of non-animal protein sources having been investigated in the past, there has long been a common misconception that animal-based protein sources were superior for muscle tissue synthesis.

PDCAAS (protein digestibility-corrected amino acid score) is a method of evaluating the quality of a protein based on both the amino acid requirements of humans and their ability to digest that protein. Quorn mycoprotein is considered to be a complete protein source and has a high PDCAAS of 0.996². To put this into context, beef has a score of 0.92 and soy has a score of 0.91³. For more information, visit our Amino Acid Lowdown Factsheet.

Animal-derived dietary protein sources, such as whey, milk, beef, and egg have all been shown to stimulate post-exercise muscle protein synthesis rates, and non-animal-based dietary protein sources have traditionally been assumed to be inferior in their capacity to stimulate muscle protein synthesis rates².

This is considered to be due to their typically slower digestibility, lower bioavailability, and lower essential amino acid (EAA) and leucine content. However, much of this narrative was based on data investigating soy protein, which has been shown to stimulate a lesser muscle protein synthetic response compared to animal-derived protein sources^{4, 5, 6}.

The research team at the University of Exeter’s Nutritional Physiology Research Group began by investigating whether the amino acids contained within mycoprotein were bioavailable; whether they appeared in the bloodstream following ingestion, meaning they had been digested and absorbed. Dunlop et al.⁷ provided healthy young males with a test drink containing either a bolus of mycoprotein (20, 40, 60 or 80 g) or 20g of milk. Mycoprotein ingestion resulted in slower and more sustained appearance of amino acids in the bloodstream compared with milk, indicating that Quorn mycoprotein could have the potential to robustly stimulate muscle protein synthesis rates.

This was a promising start, so the research team then investigated whether Quorn mycoprotein could stimulate muscle protein synthesis rates⁸ - in this instance, compared to milk protein, which can be considered a ‘gold-standard’ protein source.

Using a randomised, double-blind, parallel-group study design, researchers assessed the muscle protein synthetic response to the ingestion of a single bolus of Quorn mycoprotein compared with a bolus of milk protein, that was leucine-matched (the EAA leucine is particularly important for stimulating muscle protein synthesis).

Twenty healthy, resistance-trained young men were given either 31g milk protein or 70g Quorn mycoprotein following a bout of resistance exercise. The rate at which they were building new muscle was then measured using “tracers” in the hours following protein consumption. Results showed that Quorn mycoprotein ingestion robustly stimulated protein synthesis rates in resting and exercised muscle. While those who ingested milk protein increased their muscle growth rates by an average of 60%, those who had Quorn mycoprotein increased their muscle growth rates by more than double this. This study suggests that Quorn mycoprotein is a more effective source of protein to support post-exercise muscle protein synthesis when compared to milk protein, in healthy young men⁸.

Similarly, subsequent work by the same research group⁹ conducted in healthy young males found that a 35 g dose of branched chain amino acid (BCAA) enriched mycoprotein stimulated muscle protein synthesis rates at rest and postexercise but to a lesser extent than the 70 g mycoprotein bolus (matched in BCAA, and leucine, content). This suggests that consuming more mycoprotein, as opposed to a smaller-fortified dose, may confer the most benefit to muscle growth.