Abstract
Purpose: Ketone bodies are energy substrates produced by the liver during prolonged fasting or low-carbohydrate diet. The ingestion of a ketone ester (KE) rapidly increases blood ketone levels independent of nutritional status. KE has recently been shown to improve exercise performance, but whether it can also promote post-exercise muscle protein or glycogen synthesis is unknown.Methods: Eight healthy trained males participated in a randomized double-blind placebo-controlled crossover study. In each session, subjects undertook a bout of intense one-leg glycogen-depleting exercise followed by a 5-h recovery period during which they ingested a protein/carbohydrate mixture. Additionally, subjects ingested a ketone ester (KE) or an isocaloric placebo (PL).Results: KE intake did not affect muscle glycogen resynthesis, but more rapidly lowered post-exercise AMPK phosphorylation and resulted in higher mTORC1 activation, as evidenced by the higher phosphorylation of its main downstream targets S6K1 and 4E-BP1. As enhanced mTORC1 activation following KE suggests higher protein synthesis rates, we used myogenic C2C12 cells to further confirm that ketone bodies increase both leucine-mediated mTORC1 activation and protein synthesis in muscle cells.Conclusion: Our results indicate that adding KE to a standard post-exercise recovery beverage enhances the post-exercise activation of mTORC1 but does not affect muscle glycogen resynthesis in young healthy volunteers. In vitro, we confirmed that ketone bodies potentiate the increase in mTORC1 activation and protein synthesis in leucine-stimulated myotubes. Whether, chronic oral KE intake during recovery from exercise can facilitate training-induced muscular adaptation and remodeling need to be further investigated.
Highlights
Skeletal muscle tissue plays a pivotal role in the regulation of whole body metabolism, functional work capacity, and exercise performance (Zurlo et al, 1994; Egan and Zierath, 2013)
Skeletal muscle protein synthesis following exercise is mainly regulated by the mechanistic target of rapamycin complex 1 (Bodine et al, 2001; Schiaffino and Mammucari, 2011). mTORC1 regulates protein translation initiation and elongation via phosphorylation of the ribosomal protein S6 kinase 1 (S6K1) and the eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) (Burnett et al, 1998)
We investigated the potential of nutritional ketosis to stimulate markers of post-exercise muscle protein and glycogen synthesis, since both may enhance long-term training adaptations and facilitate muscle recovery from intense exercise (Hawley et al, 2011)
Summary
Skeletal muscle tissue plays a pivotal role in the regulation of whole body metabolism, functional work capacity, and exercise performance (Zurlo et al, 1994; Egan and Zierath, 2013). Improving the (nutritional) conditions under which exercise promotes muscle protein synthesis is important for athletes, and in clinical conditions requiring enhanced anabolic response in patients who are unable to perform high-intensity exercise. As protein synthesis is a high ATP-consuming process, mTORC1 activity is inhibited during periods of energetic stress by the AMP-activated protein kinase (AMPK; Bolster et al, 2002; Dreyer et al, 2006). During and after strenuous exercise, activation of AMPK is responsible for the delayed activation of muscle protein synthesis (Dreyer et al, 2006; Thomson et al, 2008). Rapid restoration of muscle energy balance to de-activate AMPK is important in that it enhances post-exercise mTORC1 activation, protein synthesis and eventually training-induced muscle remodeling
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