Is timing really everything?

Supplementing with protein is common among individuals engaged in resistance training, as it can increase^[1] muscle protein synthesis (MPS) and muscle growth^[2]. Many people also hold to the idea that protein timing^[3], 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^[4][5] 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^[6] 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^[7] 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.

This was a double-blind, randomized controlled trial involving 13 healthy 18-25-year-old males who exercised regularly. To be included in this study, participants needed to exercise regularly two to five days a week for one to three years and maintain regular sleep patterns (seven to nine hours per night weekly average).

Participants were randomly assigned to either a daytime group or nighttime group based on muscle size and strength to balance out the groups. The nighttime group consumed 35 grams of casein (as calcium caseinate) at night before going to sleep and 35 grams of maltodextrin earlier in the day. The daytime group consumed 35 grams of casein earlier in the day and 35 grams of maltodextrin prior to going to sleep. On workout days, the morning supplement could not be taken within three hours before or after the exercise session.

All participants engaged in a structured and supervised resistance training protocol consisting of two five-week training cycles. Each major muscle group was trained twice per week and each cycle followed a standard linear periodization of volume and intensity. Additionally, each participant logged their diet using MyFitnessPal and met with a dietitian weekly to ensure a protein intake of at least 1.8 grams per kilogram and adequate calorie intake. These targets included the casein supplements, as well as 25 grams of whey protein taken immediately after each workout session.

The preregistered primary outcomes were differences between groups for changes in lean body mass, leg press one-repetition maximum (1RM), and barbell bench press 1RM. Secondary outcomes were fat mass, body fat percentage, quadricep muscle thickness, and quadricep cross-sectional area (CSA). Additionally, the authors reported on the vertical jump test, muscle soreness, and ratings of perceived exertion (RPE) as non-preregistered outcomes. No power analysis was reported, so it is unclear what effect size this study can detect reliably.

This was a randomized double blind study involving 13 healthy 18-25-year-old males who exercise regularly. Alongside dietary advice and a supervised resistance training program, the participants were assigned to consume 35 grams of calcium caseinate either in the morning or before bed. The primary outcomes were changes in lean body mass and muscular strength, while body fat, muscle size, vertical jump height, muscle soreness, and perceived exertion were secondary outcomes.

There were no significant differences between groups for changes in any outcome except vertical jump (which improved more with daytime casein) and RPE (which was reduced more with nighttime casein). Both groups significantly increased lean body mass, leg press and bench press 1RM, muscle thickness, and muscle CSA, while reducing body fat percentage. You can check out some of the details in Figure 2.

There were no differences between groups for dietary variables. Both groups ate 2.0-2.1 grams per kilogram of bodyweight of protein, 0.5 grams per kilogram or 25% of which was provided by the casein supplement.

Both groups improved their body composition and strength without difference between one another. Dietary intake was also similar, with both groups eating 2.0-2.1 grams protein per kilogram of bodyweight.

The results of this randomized, double-blind, placebo-, diet-, and exercise-controlled trial suggest that consuming protein earlier in the day or at nighttime both produce observable increases in strength and muscle mass. These findings suggest that adequate protein and energy intake alongside an efficient training program is more important than any effect of pre-bed protein dosing. Furthermore, this research addressed some of the problems found in previous studies examining this topic: calorie and macronutrient intake did not differ between groups, and the participants underwent a supervised, effective periodized training program.

There are a few pieces of context that must be discussed though. First, this study involved young recreationally active men, meaning that the ability to generalize the study findings to other populations, such as women or the elderly, is limited.

Second, the form of casein used in this study was calcium caseinate. The naturally occurring, slowly digested form of casein found in milk is micellar casein. Micellar casein is slowly digested because it is relatively insoluble in acidic conditions (e.g., the stomach) and forms a blob^[8] that takes time to digest. Calcium caseinate is designed to allow for more rapid digestion. This may have impacted the findings, although one of the previous studies^[7] did report no effect of using micellar casein.

Third, while the nighttime casein group did have a lower RPE and the daytime casein condition had better vertical jump outcomes, these should be taken with a grain of salt; due to the very small sample size of this study coupled with the number of outcomes tested, it’s quite possible these differences were due to random chance.

Lastly, there are a few odd things about the sample size worth mentioning. Specifically, the pre-registration study description states that 33 people were enrolled in the study, while the full text states that only 20 began the study. What happened to the other 13? No explanation for this discrepancy is provided. Moreover, only 13 participants completed the study, and since no power calculation was provided, it cannot be said with certainty whether the lack of difference seen here was due to the lack of statistical power or because no difference genuinely exists. In all likelihood, this study rules out a huge difference between day and night timing, but whether moderate or smaller differences exist is still unclear.

The results of this trial suggest that consuming protein earlier in the day or at nighttime, coupled with an efficient supervised training program, both produce observable increases in strength and muscle mass in young men. However, the study may have been underpowered to detect moderate between-group differences.

As mentioned in the Introduction, some research has already been done on the topic of pre-bed casein ingestion to promote increases in lean body mass and strength. However, the current evidence base, summarized in Figure 3, is extremely limited.

Studies have demonstrated that consuming 30-40 grams of micellar casein before sleep results in elevations^[9] of muscle protein synthesis throughout the night, and that casein-derived amino acids are incorporated^[10] into muscle tissue. These observations set the stage for providing biological rationale behind pre-sleep protein.

The first longitudinal study, a 12-week RCT^[6] in young men, appeared to support the mechanistic evidence. Pre-sleep supplementation with 27 grams of casein led to significant increases in muscle size compared to a non-caloric placebo, although lean body mass and strength were unaffected. However, protein intake in this study was significantly greater with casein supplementation compared to placebo (1.9 vs 1.3 grams per kilogram of bodyweight). Were the gains due to pre-sleep protein, or more protein in general?

So far, the latter appears to be the answer. A separate RCT^[7] recruited resistance-trained men and women to supplement with 54 grams of casein either in the morning (any time before 12:00 pm) or within 90 minutes of going to bed for eight weeks while maintaining their usual exercise habits. Both groups increased their daily protein intake from 1.8 to 2.4 grams per kilogram, and there were no differences between groups for changes in body composition or muscle strength.

The study under review represents the third intervention on this topic, and it too supports the notion that total daily protein intake appears to be a more critical variable for gaining muscle mass than timing. Similar observations^[11] have been made when investigating the role of peri-workout protein supplementation.

That said, regarding pre-bed protein, it’s important not to disregard the entire study in the face of limitations. These three interventions all used healthy young adults who were recreationally active to some extent. Moreover, the matched-protein studies had a relatively high daily protein intake and an effect may be observable at lower daily protein intake levels. The type of protein may play a role, and all studies used some form of casein. Moreover, the study under review was likely underpowered to detect statistical differences between groups, and yet, it is the only study to put the participants on a controlled, periodized resistance training program. Certainly, more research into this topic is necessary to flesh out the details of when or whether it benefits someone to take casein before sleep.

There is limited evidence that continues to build on the effects of pre-sleep casein on muscle mass and strength. So far, evidence favors adequate daily protein intake more than timing, but there are still many pieces of context that require investigation.

Q. Why look at casein for nighttime protein in the first place? Why not something like whey?

Casein was selected as the nighttime protein due to its slower rate of digestion and release into the bloodstream compared to other proteins. This provides the body with an extended period of time during which amino acid levels are elevated in the bloodstream (or, if you want to use a fancy term, aminoacidemia) during sleep. One study^[12] looking at the speed of absorption between whey protein and casein exemplifies this concept; casein provided an extended plateau of aminoacidemia due to slower gastric emptying compared to whey. Another study^[4] looked at casein’s effect on fat metabolism in 12 obese men found that consuming casein before sleep did not affect fat or glucose metabolism, so it’s less likely one would have to worry about pre-bed casein impacting these factors.

Optimizing nutrition and getting enough protein in the diet can greatly affect the results people see in muscle size and strength. The study at hand looked at whether or not consuming extra protein in form of 35 grams of casein before bed would result in higher gains in muscle size and strength than consuming the same amount of protein at another time-point during the day.

The authors found no difference in either strength or size gains due to casein timing. However, some study design issues make it hard to say whether this lack of effect was real or due to the fact that the study was statistically underpowered. Even if the lack of effect is real, these results may not extend to populations other than resistance-trained young men, who were this study’s focus.