Casein Ingestion Does Not Increase Muscle Connective Tissue Protein Synthesis Rates

Abstract

Purpose This study aimed to assess the effect of dietary protein ingestion on intramuscular connective tissue protein synthesis rates during overnight recovery from a single bout of resistance exercise. Methods Thirty-six healthy, young males were randomly assigned to one of three treatments. One group ingested 30 g intrinsically L-[1-13C]-phenylalanine-labeled casein protein before sleep (PRO, n = 12). The other two groups performed a bout of resistance exercise in the evening and ingested either placebo (EX, n = 12) or 30 g intrinsically L-[1-13C]-phenylalanine-labeled casein protein before sleep (EX + PRO, n = 12). Continuous intravenous infusions of L-[ring-2H5]-phenylalanine and L-[1-13C]-leucine were applied, and blood and muscle tissue samples were collected to assess connective tissue protein synthesis rates and dietary protein-derived amino acid incorporation in the connective tissue protein fraction. Results Resistance exercise resulted in higher connective tissue protein synthesis rates when compared with rest (0.086 ± 0.017%·h−1 [EX] and 0.080 ± 0.019%·h−1 [EX + PRO] vs 0.059 ± 0.016%·h−1 [PRO]; P < 0.05). Postexercise casein protein ingestion did not result in higher connective tissue protein synthesis rates when compared with postexercise placebo ingestion (P = 1.00). Dietary protein-derived amino acids were incorporated into the connective tissue protein fraction at rest, and to a greater extent during recovery from exercise (P = 0.002). Conclusion Resistance exercise increases intramuscular connective tissue protein synthesis rates during overnight sleep, with no further effect of postexercise protein ingestion. However, dietary protein-derived amino acids are being used as precursors to support de novo connective tissue protein synthesis.

Exercise Plus Presleep Protein Ingestion Increases Overnight Muscle Connective Tissue Protein Synthesis Rates in Healthy Older Men

“…PRO) to be utilized for de novo muscle connective tissue protein synthesis during overnight recovery. The present findings align with our recent work demonstrating that dietary protein-derived amino acids are incorporated into de novo muscle connective tissue protein at rest and, to a further extent, during postexercise recovery in younger individuals (Trommelen et al, 2020). Altogether, these data reinforce our findings that resistance-type exercise promotes the remodeling of muscle connective tissue and illustrate the potential role of dietary protein to support postexercise skeletal muscle tissue adaptation in older individuals.…”

“…Resistance-type exercise is the most potent anabolic stimulus for skeletal muscle tissue protein. We have recently demonstrated that a bout of resistance-type exercise increases muscle connective tissue protein synthesis rates in younger individuals (Trommelen et al, 2020). As hypothesized in the present study, a bout of resistance-type exercise combined with presleep casein protein ingestion increased postprandial muscle connective tissue protein synthesis rates by ∼100% during overnight recovery in older men (Figure 4a).…”

“…The impact of food ingestion and physical activity on muscle connective tissue protein synthesis rates has not yet been fully elucidated, especially in the older population. Exercise increases muscle connective tissue protein synthesis rates in both younger and older individuals (Cuthbertson et al, 2006;Dideriksen et al, 2016;Holm et al, 2010;Mikkelsen et al, 2015;Moore et al, 2005;Trommelen et al, 2020). However, nearly all of the existing studies have shown no impact of protein ingestion on muscle connective tissue protein synthesis rates at rest or during postexercise recovery (Babraj et al, 2005;Dideriksen et al, 2016Dideriksen et al, , 2011Holm et al, 2010;Mikkelsen et al, 2015).…”

Pre-sleep casein protein ingestion: new paradigm in post-exercise recovery nutrition

“…A recent study also reported that intramuscular connective tissue protein synthesis rates were not significantly increased in healthy young males who ingested 30 g of casein protein 30 minutes before sleep following resistance exercise, compared to those who ingested a placebo 23 . A possible reason for these negative results could be the amount of casein protein ingested as 40-48 g of casein protein had positive effects in previous studies 8,9 , whereas only 30 g of casein protein was ingested in the studies showing no effects 22,23 . However, a recent study involving active males and females reported that the ingestion of 40 g of casein protein 30 minutes before sleep after repeated high-intensity drop jumps did not affect acute functional recovery indices such as countermovement jumps or pressure-pain threshold 2 , indicating that the results of the previous studies might not be due to the amount of casein protein ingested alone.…”

Comprehensive assessment of post-prandial protein handling by the application of intrinsically labelled protein in vivo in human subjects

“…The use of highly enriched intrinsically labelled protein has consistently shown that dietary protein-derived amino acids are utilised for de novo muscle protein synthesis across a wide variety of populations and can be modulated by various dietary and physiological conditions (3,27,51,52) . Ingested protein delivers amino acids as precursors for de novo muscle protein synthesis in mixed muscle protein (3) , and has also been detected in various isolated muscle protein fractions, such as myofibrillar (51) , mitochondrial (6) and connective tissue (53) proteins. Our research group has applied intrinsically labelled protein to demonstrate that the ingestion of 20 g micellar casein protein results in the incorporation of approximately 2 g (about 10 %) dietary protein-derived amino acids into muscle tissue protein during a 5 h post-prandial period (3) .…”