Our observation that protein administered during sleep is effectively digested and absorbed provided proof-of-principle that the gut functions properly during sleep [ 23 ]. However, nasogastric tube feeding does not represent a feasible feeding strategy for athletes. Therefore, our next step was to assess if protein ingestion prior to sleep would represent an effective dietary strategy to increase muscle protein synthesis rates during overnight post-exercise recovery [ 24 ]. Therefore, we studied recreational athletes during overnight recovery from a single bout of resistance-type exercise performed in the evening after a full day of dietary standardization. Immediately after exercise, all athletes ingested a recovery drink containing 20 g protein to maximize muscle protein synthesis rates during the acute stages of post-exercise recovery [ 4 24 ]. As explained above, this prescribed recovery strategy does not suffice to maintain elevated muscle protein synthesis rates during more prolonged overnight sleep [ 21 ]. Therefore, we provided subjects with either 40 g casein protein or a placebo drink immediately prior to sleep. In line with intragastric protein administration during sleep [ 23 ], the bolus of protein ingested prior to sleep was properly digested and absorbed throughout overnight sleep. The greater plasma amino acid availability following pre-sleep protein ingestion improved the overnight whole-body protein balance, allowing the net protein balance to become positive. In line, muscle protein synthesis rates were approximately 22% higher during overnight recovery when protein was ingested prior to sleep when compared to the placebo treatment. From these data we concluded that pre-sleep protein ingestion represents an effective dietary strategy to further augment the skeletal muscle adaptive response to resistance-type exercise training ( Figure 1 ).

To test this hypothesis, we assessed the impact of pre-sleep protein feeding to facilitate the skeletal muscle adaptive response to prolonged resistance-type exercise training [ 25 ]. Specifically, we selected healthy young men to participate in a 12-week resistance-type exercise training program (three exercise sessions per week) during which they ingested either 27.5 g of protein prior to sleep, or a non-caloric placebo. Muscle mass and strength increased to a greater extent in the group that ingested protein prior to sleep. These results indicate that protein supplementation prior to sleep represents an effective dietary strategy to augment the gains in muscle mass and strength during resistance-type exercise training. It remains to be established what dose and type of pre-sleep protein should be used to further optimize overnight muscle protein synthesis rates and, as such, can support greater gains in muscle mass and strength.

It should be noted that the ingestion of the pre-sleep protein supplement in both our acute and long-term studies was compared with a non-protein placebo, and not compared with protein supplementation provided at other time points. Therefore, we can only speculate on the surplus benefits of pre-sleep protein provision when compared to other time points. It can be speculated that the greater gains in muscle mass and strength are, at least partly, attributed to the pre-sleep timing of the protein supplement, as the vast majority of studies in which protein has been supplemented immediately before and/or after exercise do not show an increase in muscle mass gains when compared to a placebo [ 26 ]. However, it has been suggested that protein supplementation increases muscle mass gains mainly as a function of increased total protein intake, rather than the specific timing of a protein supplement [ 27 28 ]. As a meta-analysis was required to demonstrate that additional protein intake augments training-induced muscle hypertrophy [ 26 ], it seems unlikely that a possible positive effect of protein timing (i.e., protein supplementation at a time point compared to protein supplementation at different time point) on muscle mass gains can be detected in a longitudinal study. While it is currently unclear whether pre-sleep protein ingestion is superior to protein ingestion at a different time point, we propose that a more relevant question is whether pre-sleep protein ingestion is additive to protein intake earlier in the day. We suggest that athletes should aim to ingest sufficient protein intake at every meal to maximize muscle protein synthesis until the next meal. We have recently shown that the ingestion of large amounts of protein in the early post-exercise recovery phase does not compromise the muscle protein synthetic response to protein ingestion at a later stage [ 29 ]. This suggests that every meal moment represents a unique opportunity to stimulate muscle protein synthesis and that the muscle protein synthetic response to each meal may be additive. In addition, we have recently shown that athletes typically consume well above 1.2 g protein/kg/day, with the majority of protein consumed during the three main meals, and only a small amount of protein eaten as an evening snack (~7 g) [ 30 ]. As such, additional pre-sleep protein ingestion represents a practical strategy to increase the total daily protein intake, add another meal moment, and increase the overnight muscle protein synthesis rates; this effect is likely additive to muscle protein synthesis rates observed throughout the day.