Protein timing during the day and its relevance for muscle strength and lean mass

Protein consumption and its association with changes in body composition, muscle function and different strategies to optimize the muscle protein synthetic response have received considerable attention. However, we are not aware of any epidemiological study examining the time-of-day consumption (afternoon versus evening) of protein on strength and lean mass. The purpose was to examine the associations between afternoon and evening protein consumption, at different protein thresholds (i.e. 15, 20, 25 and 30 g), in relation to leg lean mass and knee extensor strength in men. Dietary protein consumption was assessed using 24-h dietary interview format. Knee extensor strength was measured on an isokinetic dynamometer. Leg lean mass was estimated from whole-body DXA scans. Participants who consumed 20 g, 25 g and 30 g of protein in the evening had greater leg lean mass than those who consumed protein in the afternoon (P<0·05). However, there was no difference in leg lean mass for 15 g of protein consumption in the evening compared to the afternoon (P>0·05). For strength, there were no differences between evening and afternoon consumption of protein for 15 g, 20 g or 25 g (P>0·05); however, those consuming at least 30 g of protein in the evening had greater knee extensor strength compared to those consuming similar amounts in the afternoon (P = 0·05). These findings suggest that evening protein consumption is associated with greater leg lean mass and knee extensor strength when compared to afternoon protein consumption. Based on these findings, we cautiously hypothesize that there may be a circadian rhythm in muscle protein metabolism.