Plain language summary
Protein intake prior to overnight sleep has been shown to stimulate muscle protein synthesis overnight and increase muscle mass. This randomised, placebo-controlled, double-blind study of 36 healthy young men compared the effects of pre-sleep casein and whey protein, following a bout of endurance training in the evening. Outcome measures were overnight protein synthesis rates in microfibrils (the contractile organelle of muscle cells) and mitochondria (the energy producing organelle). Ingestion of whey protein resulted in a statistically significantly higher rates of both microfibrillar and mitochondrial protein synthesis compared to placebo. Results for casein were intermediate and not significantly different from either placebo or whey. Both casein and whey protein intake led to a significant increase in circulating total and essential amino acids overnight, compared to placebo, with the whey protein leading to a quicker and casein to a slower but more sustained increase, although the overall increase (area under the curve) did not differ between the two protein groups. There were no differences in sleep, hunger or energy intake at breakfast between groups. The authors conclude that pre-sleep protein intake following endurance exercise increases both microfibrillar and mitochondrial protein synthesis overnight, with casein not being superior to whey.
Abstract
BACKGROUND Casein protein ingestion prior to sleep has been shown to increase myofibrillar protein synthesis rates during overnight sleep. It remains to be assessed whether pre-sleep protein ingestion can also increase mitochondrial protein synthesis rates. Though it has been suggested that casein protein may be preferred as a pre-sleep protein source, no study has compared the impact of pre-sleep whey versus casein ingestion on overnight muscle protein synthesis rates. OBJECTIVE We aimed to assess the impact of casein and whey protein ingestion prior to sleep on mitochondrial and myofibrillar protein synthesis rates during overnight recovery from a bout of endurance-type exercise. METHODS Thirty-six healthy young men performed a single bout of endurance-type exercise in the evening (19:45 h). Thirty minutes prior to sleep (23:30 h), participants ingested 45 g of casein protein, 45 g of whey protein, or a non-caloric placebo. Continuous intravenous L-[ring-13C6]-phenylalanine infusions were applied, with blood and muscle tissue samples being collected to assess overnight mitochondrial and myofibrillar protein synthesis rates. RESULTS Pooled protein ingestion resulted in greater mitochondrial (0.087 ± 0.020 vs 0.067 ± 0.016%·h-1, p = 0.005) and myofibrillar (0.060 ± 0.014 vs 0.047 ± 0.011%·h-1, p = 0.012) protein synthesis rates when compared with placebo. Casein and whey protein ingestion did not differ in their capacity to stimulate mitochondrial (0.082 ± 0.019 vs 0.092 ± 0.020%·h-1, p = 0.690) and myofibrillar (0.056 ± 0.009 vs 0.064 ± 0.018%·h-1, p = 0.440) protein synthesis rates. CONCLUSIONS Protein ingestion prior to sleep increases both mitochondrial and myofibrillar protein synthesis rates during overnight recovery from exercise. The overnight muscle protein synthetic response to whey and casein protein does not differ. CLINICAL TRIAL REGISTRATION NTR7251 .
Methodological quality
Jadad score
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2
Allocation concealment
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Not applicable
