Supplementing with protein is common among individuals engaged in resistance training, as it can increase muscle protein synthesis (MPS) and muscle growth. Many people also hold to the idea that protein timing, such as prior to sleep or post workout, may play a role in optimizing muscle growth and strength. However, athletes are sometimes tentative to consume protein or other macronutrients prior to sleep, thinking that it will slow the breakdown of body fat. However, research has suggested that protein consumption before sleep does not affect glucose or fat metabolism.
Of course, just because one can dose protein before bedtime doesn’t mean one should. But if one did choose a type of pre-bed protein, it would probably be casein, since, as shown in Figure 1, essential amino acids (EAA) from casein get slowly released into the bloodstream and can reliably stimulate muscle protein synthesis overnight. But this doesn’t directly address the question of casein timing; perhaps daytime casein would do an equally effective job at stimulating muscle protein synthesis.
The effect of casein dose timing has been previously researched, but there are some problems with the evidence base that makes it difficult to draw firm conclusions. For instance, one study looked at the effects of supplementing 27 grams of casein prior to sleep on muscle size in healthy young men involved in resistance exercise. The researchers found an effect. The only problem is that the protein intake in the treatment group wound up being 0.7 grams per kilogram of bodyweight larger in the treatment group, making it hard to say whether the results were due to overnight timing or increased protein intake.
Another study looked at resistance-trained men and women who consumed 54 grams of micellar casein either in the morning or within 90 minutes of going to bed for eight weeks while maintaining their normal exercise habits. Both groups increased their total daily protein intake from 1.8 to 2.4 grams per kilogram, yet, strangely, neither group experienced changes in body composition or muscle strength. This could possibly be because the participants continued their usual training routine, which may have been suboptimal.
Given the issues with the research into the matter of pre-bed casein, the authors of the study under review aimed to examine the effects of dosing casein earlier in the day versus before bed on bodyweight, muscle mass, and strength while undertaking a supervised, effective training routine.
In theory, protein dosing before bedtime could aid in muscle protein synthesis and improve muscle strength and growth. A natural choice for a pre-bed protein would be casein. However, previous research looking into whether casein timing matters had some methodological issues, which makes it difficult to draw firm conclusions about the effects of casein timing alone. The aim of the study under review was to examine the effects of pre-bed casein while avoiding these previous problems.