The ingestion of casein before sleep, or any other protein for that matter, has been a popular strategy for bodybuilders, athletes and fitness enthusiasts for as long as I can remember. In this article, I will examine what the scientific literature has to say about the matter and whether it lives up to its hype.
Background & Rational
Casein is a protein found in mammalian milk, making up roughly 80% of the protein found in cows’ milk (the remaining 20% consists of whey). Casein is more slowly digested than whey, with estimated absorption rates of around 6.1 and 8-10 grams per hour, respectively (1). Casein’s slower rate of digestion is primarily related to its structure since its coagulation in the stomach slows the rate of gastric emptying. Indeed, this slower rate of digestion of casein, compared with the rapid digestion of whey results in a more sustained elevation in blood amino acid levels and a greater inhibition of protein breakdown, albeit with a smaller stimulation of protein synthesis (2). As such, the basic premise behind the ingestion of casein before bed is that its positive effects on muscle protein synthesis (MPS) and muscle protein breakdown (MPB) will augment the adaptive response to resistance exercise as well as stopping the atrophy fairy from dining on your well earned muscles whilst you sleep.
What does the research say?
To date, and to my knowledge, only four studies have looked at the ingestion of casein before sleep and its effects on adaptation to exercise (i.e. muscle hypertrophy and strength) and/or muscle protein balance (Table 1) (3,4,5,6).
Table 1. Casein ingestion before bed - study overview
Given the prevalence of age-related muscle degeneration (sarcopenia), in the first study of its kind, van Loon’s research group (3) demonstrated that 40g of casein administered by nasogastric tube feeding two hours into sleep increased plasma amino acid availability and stimulated skeletal muscle MPS, thus improving overnight whole body protein balance in a group of elderly men. While the observations in this study may have limited applicability to young trainees, especially those engaging in regular weight training, it does demonstrate that night time protein ingestion is a potential feeding strategy that can be incorporated to help offset muscle mass losses associated with ‘anabolic resistant’ individuals (i.e. the elderly).
In a more recent study, the same research group demonstrated that 40g of casein ingested 30 minutes before sleep improved overnight recovery to a greater extent than a non-caloric placebo following a single bout of resistance exercise (eight sets of both machine leg presses and leg extensions) in a sample of 15 recreationally active men (4). During the 7.5h testing period, measures of whole body protein balance were significantly greater in the experimental group relative to placebo (primarily due to the 22% increase in protein synthesis as opposed to a reduction in protein breakdown).
Though the authors acknowledge that the study was designed as a ‘proof of concept’ (i.e. to examine whether pre-bed dietary protein is effectively absorbed, with the resulting increase in amino acid availability stimulating MPS), many fitness professionals and academics, alike, cite this study as ‘proof’ that pre bed casein ingestion is somehow required, and therefore indiscriminately recommended for those looking to optimise recovery and muscle growth after training.
Notwithstanding the fact that it seems obvious that casein would be properly digested at any time of the day (to me, at least), it is difficult to determine whether such improvements seen in the protein group were due to the specific timing of ingestion in relation to sleep, or simply because they received an additional 40g of protein. Indeed, the control group was reported to have received 1.2 g/kg of protein, whereas the additional 40g of casein given to the experimental group raised their day’s protein intake from 1.2 to 1.76 g/kg. If we look at the daily protein recommendations for strength athletes (1.3-1.8 g/kg) (7), what we essentially have is a comparison of inadequate vs. adequate protein intakes. It is therefore hardly surprising that the experimental arm outperformed the control (at least when looking at acute markers of adaptation and recovery). Relating to such acute markers, caution is required when interpreting acute findings with regards to their translation to long-term phenotypic changes (e.g. muscle hypertrophy) (8). Fortunately, there are a couple of studies that attempt to shed some light on this question.
In a very recent study, again, van Loon’s research group demonstrated that 27.5g of a casein blend (50% casein, 50% casein hydrolysate) plus 15g CHO ingested immediately before sleep improved muscle mass and strength gains to a greater extent than a non-caloric placebo during a 12-week (3 x / week) resistance training programme in a sample of 41 recreationally active men (5). After 12 weeks of performing eight sets of both machine leg presses and leg extensions (plus either two sets of chest press and horizontal row or lat pull down and shoulder press, which were alternated at every session) three times/week, changes in quadriceps muscle cross sectional area (CSA), type 1 & 2 fibre size, and total 1RM were improved to a greater extent in the protein supplemented individuals. Again, whilst this study seems to support the practises of the casein camp, it suffers from the same main limitation of the previous, in that the addition of the protein drink bumped the daily protein intake from 1.3 to 1.9g/kg in the experimental condition, whereas it remained at 1.3g/kg in the control group. This does not necessarily rule out a timing effect for casein ingestion, rather, it is just not possible to determine with this study design due to the two independent variables (quantity and timing of protein). The authors of the study rather elegantly echo the protein-matched issue by stating, “In the present study, ingestion of the protein supplement before sleep was not compared with other time points of ingestion. As such, we can only speculate on the surplus benefit(s) of the protein supplement being provided before sleep as opposed to other time points throughout the day.” Given this acknowledgement, I am hopeful that we will see this study replicated but with the protein-matched issue addressed.
On further examination of the results, when looking at the changes in whole body lean mass, although there was a significant training effect, there was no significant interaction effect when analysed with a split-plot model with treatment (protein vs. placebo) and training (before vs. after training). In other words, the 12 weeks of training increased lean mass in both the protein and placebo groups (1.9 vs. 1.7kg, respectively), though this was not significantly different between groups. Furthermore, the mean pre-training body masses of the protein and placebo groups were 76.9 and 80kg, respectively. Though differences in body mass were non-significant, it is possible that the lighter participants in the protein condition had a greater capacity for growth, a factor that may have influenced the observations. As such, these data nicely demonstrate the difference between statistical significance and practical/clinical significance (i.e. whether the difference is meaningful in the real world).
After scouring the literature on this topic, I was surprised to see that a paper had been published in 2009 that examines the effect of nighttime casein ingestion in addition to matching protein across groups (6). In a crossover study conducted in 13 young men, Burk and colleagues examined the effects of 70g (82% casein) of protein split into two doses, with one group consuming 35g at 22:30 (Time divided supplementation regimen: TDR) and the other group consuming 35g of the protein supplement immediately before resistance training (16:00) (Time focused supplementation regimen: TFR) on body composition measures (via DXA) and maximal strength (1RMs for squat and bench press) for two (one block for each condition), 8-week resistance training blocks (4x/week with 3-4 sets per muscle group at 75-80% 1RM; Mon & Thu – chest, back and shoulders; Tue & Fri – legs, back extensors and arms). The remaining 35g of the protein supplement were consumed at 10:00: the mid-point between breakfast (08:00) and lunch (12:00) in each group. Body mass increased slightly (though non-significantly) in both groups (0.7 & 0.8kg) in the TDR or TFR conditions, though changes in fat free mass (FFM) were significantly greater in the TDR condition (+1.75kg) compared with the TFR condition (+1kg). Though non-significant, fat mass decreased in the TDR condition (-0.5kg) and increased in the TFR condition (+0.2kg). Combined with the increase in FFM in the TDR condition, this explains the lack of change in body weight seen between conditions. Squat and bench press 1RMs were significantly improved in both conditions.
The addition of the protein supplements resulted in an increase in daily protein consumption from 1.4 & 1.3 to 2.3g/kg in the TDR and TFR groups, respectively. As such, the 2.3g/kg consumed across groups with the addition of supplementation would be fairly representative of intakes typically seen in strength athletes (9), making the conclusions more relevant to such populations (notwithstanding the use of untrained participants in this investigation).
Like all studies, this one is not without its limitations. For instance, misreporting is likely since participants’ dietary intake was uncontrolled apart from adhering to the supplementation regimen and being instructed to “maintain ordinary eating habits” (10). Further, participants in the TDR group were expected to go from 12:00 to 20:00 without eating, compared with a protein feeding at 16:00 in the TFR condition (right before the training session), it seems likely that the TDR group would have consumed something (that probably included protein) during this eight-hour period. If my speculations are correct, they would appear to explain both the increase in body mass observed, as well as the superior gains in FFM in the TDR condition; the latter owing to a better distribution of their daily protein intake (which was perhaps also higher than the TFR group).
On the surface, this study appears to support the use of nighttime casein ingestion, but given the aforementioned limitations and lack of measures of protein turnover, the answer of to the question of this article remains inconclusive.
Looking at the forest / other considerations
With respect to dietary protein and its timing of ingestion, it is important to put things into perspective. In Figure 1 you can see my suggested hierarchy of importance in relation to protein ingestion. This pyramid takes into account both protein research and practical relevance (the former of which is not always practically relevant). For instance, if daily protein is insufficient, the remaining factors become increasingly important and vice versa. This idea is supported by a relatively recent review (11) as well as a meta-analysis (12) by Aragon and colleagues, who concluded that any benefits seen with specific timing of ingestion of protein in relation to resistance exercise are likely due to an increase in overall protein intake (i.e. the addition pre/post exercise protein results in non-matched overall intakes across subject groups).
In a similar vein, if someone were consuming ample amounts of protein that was evenly distributed throughout the day, it is difficult to see how improving protein quality (for the purposes of this article defined as the proportion of essential amino acids and branched chain amino acids, particularly leucine, in a given protein source) or the ingestion of a shake immediately after training, or prior to bed, would make much difference in terms of training adaptation, muscular hypertrophy or retention. In this example, if evenly distributed, an abundance of protein (>2g/kg) despite a potential compromise in quality would still maximise the anabolic response to protein feeding, although not as efficiently as higher quality protein sources (on a gram for gram basis) (13). A possible exception to this would occur in vegans, in which adequate amounts of all of the essential amino acids may not be present in their diet (14).
Figure 1. Dietary protein: a hierarchy of importance
In the absence of sufficient data to fully answer the question raised in this article, we can run through a theoretical example of an individual (an 80kg male at roughly 10% body fat) that is doing most things right with respect to the bottom three tiers of the pyramid in Figure 1. From there, we can examine whether the addition or inclusion of casein before bed could improve muscle hypertrophy or muscle retention, respectively.
Skeletal muscle hypertrophy
For the purpose of this exercise, I will set daily protein at 2.5g/kg predominantly coming from animal sources (e.g. meat, poultry, eggs, dairy). For an individual in a neutral or positive energy balance, such an intake of high quality protein appears to be more than sufficient for maximising rates of muscle anabolism (7,13). In terms of how we would then distribute this amount of protein throughout the day, I will briefly summarise my article on meal frequency (15) below:
- The amount of muscle mass a person has depends on the long-term relationship between muscle protein breakdown and synthesis (i.e. protein turnover).
- A threshold amount of leucine of 2-3 g (~ roughly 0.05g/kg body weight) is thought to exist in order to maximise MPS, with no apparent further stimulation of MPS with higher intakes (16).
- This would translate to 25-37.5 g of leucine-rich protein sources (e.g. whey, casein, beef, chicken).
- Due to the apparent refractory nature of MPS, it would seem that eating meals spaced every 3/4-5 hours apart would optimise MPS within a 24-hour period (17).
- However, it appears that there is more to muscle gain than frequently stimulating MPS; the reasons being as follows:
o A recommendation for higher daily amounts of protein than is likely to ‘max’ out MPS (7,22).
o A decrease in muscle protein breakdown due to protein feeding (18).
o Concept of the anabolic drive and hidden signaling pathways involved in protein turnover and AA oxidation (19).
o Real-world observations of excellent improvements in muscle mass despite theoretically ‘too high/too low’ meal frequencies (e.g. the intermittent fasting folk) (20).
o Apparent lack of effects on lean body mass (LBM) with reduced meal frequencies whilst dieting, providing that daily protein is sufficient (i.e. <3 meals per day) (21).
- It therefore seems that total protein intake is the most important variable, and how this intake is distributed impacts body composition to a lesser degree.
- For these reasons, I do not see it being necessary for meal frequency to be higher than the typical 4-6 meals per day for most people seeking decent rates of muscle gain.
- Though it is unknown whether moving to an ‘optimal frequency’ would be of benefit, it seems unlikely in the real world; and if so, it may only benefit the elite physique looking for that 1% over their competition. Eating less than twice per day may compromise rates of muscle gain (22), however, no solid data exist to make definitive conclusions.
Taking this summary into account, and the example athlete’s preferences, I would split this daily protein intake into 4-6 meals eaten roughly every 3-5 hours (33-50g per meal). Now that the example athlete has the bottom three tiers covered, based on my interpretation of the available data, as well as my experience with both physique and performance athletes, I see no reason how the addition or inclusion of pre bed casein would be advantageous for their goal for the following reasons:
- 2.5g/kg of protein for the goal of muscle gain is already conservatively high, so I see it unlikely that the addition of casein would enhance gains further.
- Moving one of the protein feedings immediately prior to sleep in the form of casein is unlikely to outperform another high quality protein that would already be consumed in close proximity to sleep (<3 hours).
Skeletal muscle retention
In terms of skeletal muscle retention, I would keep protein sources the same and set daily protein at around 3g/kg; the rationale for the higher protein intake during dieting being due to its apparent muscle protein sparing effects (23). As alluded to in the meal frequency’ summary above, protein distribution seems to be much less important for maintaining muscle mass, compared with building it. Despite some of its questionable conclusions (24), according to the ISSN position stand on meal frequency, a reduced meal frequency does not appear to compromise LBM under hypocaloric conditions in the presence of sufficient protein intakes (20). That is, eating 10 times per day as opposed to once or twice per day does not seem to make much difference with regards to the sparing of LBM on a diet (assuming you are getting sufficient protein that is). With this in mind, I would still be inclined to keep the example athlete’s distribution the same in order to cover bases, as well as to avoid changing things up too much between transitions of body composition goals (e.g. muscle gain or fat loss). Given these factors, I can therefore see no reason for the inclusion of casein pre-bed to enhance muscle mass preservation during an energy deficit.
Finally, it is important to highlight that the very nature of science is tentative. As such, unless more externally valid studies are undertaken that directly examines the question of this article, no definitive conclusions can be made. That said, if everything else is optimised with regards to protein ingestion, and indeed casein before sleep does turn out to be beneficial, it is worth mentioning that casein is not the only slowly digested protein source. For instance, cooked egg protein, pea protein, milk protein and soy protein isolate have estimated rates of digestion of roughly 2.9, 3.5, 3.5 and 3.9g/hour, respectively, compared with roughly 6.1g/hour of casein protein.1
Summary and practical application
Given the slowly digesting nature of casein, its ingestion prior to sleep has become a popular strategy for athletes looking to minimise muscle loss and enhance muscle gain.
Both short and longer-term studies examining the efficacy of this practise are fraught with limitations in that true inferences about the specific timing of ingestion of casein cannot be made. Nonetheless, the ingestion of casein prior to bed does seem to be a good strategy to incorporate more protein into a diet in which it is lacking.
In the absence of sufficient data, when looking at things from a theoretical perspective, it does not seem likely that casein ingestion before bed would be advantageous for someone who is getting sufficient amounts of high quality protein, distributed throughout the day; strategies that most conscientious athletes would already be doing.
As such, my recommendations to individuals looking to optimise rates of muscle gain, adaptation or preserve muscle mass are as follows:
- Consume sufficient quantities of quality protein relevant to your goal.
- Spread this daily protein intake evenly across 4-6 meals every 3-4 hours.
- Once these factors are consistently in place, feel free to experiment with pre-bed protein feeding. If you do not feel/see a benefit to this, disregard this protocol and carry on nailing the stuff that does matter.
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