Nutrient Timing Endures: Circadian Rhythm Protein Timing

When I started bodybuilding some 7 years ago, everyone I knew ate big breakfasts and 6 meals a day. It was also commonly accepted that carbs should be limited to the start of the day while ‘slow’ forms of energy should be consumed later in the day. Before bed, people said to take casein with some fat to prevent night time catabolism. I can’t even begin to recount how often I’ve eaten oatmeal with whey for breakfast and cottage cheese with flax seed before bed.

These days, things are a lot different. Pretty much all of the forms of nutrient timing I just listed are known to be ineffective. You can skip breakfast without sacrificing gains to cortisol, absolute meal frequency is irrelevant, carbs and fats can be eaten at any time of day and you can go without food for a long time without losing muscle.

These changes have caused many people to be skeptical of nutrient timing as a principle. This skepticism is most strongly represented by the nihilist approach to dieting called IIFYM: if it fits your macros. IIFYM in its purest form (!) states that all that matters in a diet is its macronutrient composition. The amounts of carbs, fat and protein and the resulting total energy intake are all that matters according to pure IIFYM. When you eat those macros is irrelevant: nutrient timing doesn’t enter into it and can go the way of the dodo. While simplistic, this skeptical approach to nutrition is much more scientific than the prevailing broscience attitude of “let’s try everything that sounds cool even if it’s just a theory without any empirical support”.

In the absence of evidence, there is no reason to believe a statement. However, there actually is evidence that IIFYM may be missing something. This something, or something of this something, is circadian rhythm protein timing (CRPT). Let’s look at the evidence.

Circadian Rhythm Protein Timing

CRPT is a form of nutrient timing, specifically protein timing, relative to your circadian rhythm – your ‘biological clock’ – just like the (false) ‘anabolic window theory’ is carb and protein timing relative to training sessions. Simply put, CRPT just refers to how you spread your daily protein intake over the day, taking into account that different people may sleep at different times.

Let’s look at the research on CRPT. The following studies all controlled for daily protein and energy intake.

Burk et al. (2009) used a long term cross-over design to compare 2 groups of men performing serious resistance training and eating a diet containing more than sufficient protein. The only difference between the groups was the timing of a protein supplement containing 70 grams of protein. One group received it at midday, 8 hours after awakening, and the other group received it 90 minutes before going to sleep. The group receiving the protein later in the day gained significantly more muscle mass than the group receiving it at midday. In fact, the protein timing made the difference between maintaining and gaining muscle mass.

So, not only can CRPT be beneficial, it cannot be said that nutrient timing is strictly less important than energy intake or that nutrient timing is below energy intake in the hierarchy of dietary importance. It’s not that simple. Even if you train hard and eat the right things, eating them at the wrong time can stop you from getting bigger. And it gets even better: CRPT works for weight loss as well.

Keim  and bros (1997) used a long term cross-over design to compare two groups on a weight loss diet in a metabolic ward. The only difference between the groups was when most of the food was consumed. One group consumed 70% of their total energy intake in the AM and the other group consumed 70% of their total energy intake in the PM.  Both groups got up before 8AM. The PM group had better muscle retention during the diet and a higher reduction in body fat percentage than the AM group.

That’s 2 well controlled studies in favor of eating much of your daily protein intake later in the day. However, these studies cannot tell us if it was the energy or just the protein timing that caused the positive effects.

Enter Jordan et al. (2010). These white-coat-wearing amigos compared two groups receiving a carbohydrate and a protein beverage at breakfast and about 10 hours after waking up and they measured nitrogen balance, a measure of daily protein balance and lean tissue growth. One group received the carbs at breakfast and the protein later in the day and the other group received the carbs later in the day and the protein at breakfast. The group receiving the protein later in the day had a significantly more positive nitrogen balance than the group receiving the protein at breakfast. Because the study authors controlled for carb and therefore energy timing, only the protein timing could have caused this difference. The most remarkable thing about this study is that the protein beverage only contained 15 grams of protein in a diet containing more than sufficient protein and still they found a significant effect.

Putting the CR in CRPT

Why does CRPT work? One explanation is that it’s because in these studies the protein was more spread out over the day. However, this theory would also predict that increasing meal frequency would result in greater protein balance and we know that’s not true. Instead, I think the mechanism behind CRPT is similar to that of the anabolic window. The anabolic window theory is of little relevance because A) the anabolic window lasts a

bout 48 hours and B) training sessions are often interspersed by meals, so there is normally a constant flux of amino acids during the entire time regardless of the precise meal timing. That’s the central message: the anabolic window is a period during which your body is ext

ra sensitive to nutrients. Some say all the magic happens in the anabolic window, but I think there is another period like that where the real magic (get it? Real magic) happens. It’s called sleep.


There is natural diurnal variation in anabolic hormones like growth hormone and testosterone. Care should always be taken to interpret transitive changes in these hormone concentrations, as this kind of reasoning forms the basis for most broscience, but in the case of the circadian rhythm the changes aren’t insignificant. The variation occurs day in day out and is very robust and large relative to the mean. Look at the graph below, which shows how growth hormone fluctuates every day for people sleeping between 00:00 and 08:00h (Ken et al., 2005).

It seems to me like having a royal supply of amino acids in your blood between 21:00 and 09:00 is a pretty good idea to put that growth hormone to use. The same holds for testosterone, which is shown in the graph below (Raff, & Sluss, 2008 – I didn’t make those names up).

Sleep is like restoration mode for your body. It never made sense to me that half the theories in the fitness industry are based on anabolic hormones yet sleep is neglected. The advice not to eat before bed is foolish. As a recent study showed, “protein ingested immediately before sleep is effectively digested and absorbed, thereby stimulating muscle protein synthesis and improving whole-body protein balance during postexercise overnight recovery” (Res et al., 2012).


Energy intake and macros are far from all that matters in a diet and can’t be considered strictly more important than nutrient timing. CRPT, the timing of your protein intake over the day, can aid both muscle gains during a bulk and muscle retention during a cut. It’s so important that it can make the difference between significant hypertrophy and complete stagnation. There is still much that needs clarification by future research, but all current evidence points in the direction that you should consume a significant amount of your daily protein intake later in the day. Whether energy timing also has an effect and what the optimal timing is remain uncertain at this point.

Let CRPT serve as an illustration that, even in a time where the strength community is getting back to basics, sometimes it’s the little things that make all the difference.

Take home message: Consume at least a single meal with a good portion of protein in the hours before going to sleep.


  1. Burk A, et al. Time-divided ingestion pattern of casein-based protein supplement stimulates an increase in fat-free body mass during resistance training in young untrained men. Nutr Res. 2009 Jun;29(6):405-13.
  2. Keim NL, et al. Weight loss is greater with consumption of large morning meals and fat-free mass is preserved with large evening meals in women on a controlled weight reduction regimen. J Nutr. 1997 Jan;127(1):75-82.
  3. Nitrogen balance in older individuals in energy balance depends on timing of protein intake. Jordan LY, Melanson EL, Melby CL, Hickey MS, Miller BF. J Gerontol A Biol Sci Med Sci. 2010 Oct;65(10):1068-76.
  4. Pre-analytical issues for testosterone and estradiol assays. Raff H, Sluss PM. Steroids. 2008 Dec 12;73(13):1297-304.
  5. Protein Ingestion before Sleep Improves Postexercise Overnight Recovery. Res PT, Groen B, Pennings B, Beelen M, Wallis GA, Gijsen AP, Senden JM, VAN Loon LJ. Med Sci Sports Exerc. 2012 Aug;44(8):1560-9
  6. The dynamics of growth hormone (GH) secretion in adult cancer survivors with severe GH deficiency acquired after brain irradiation in childhood for nonpituitary brain tumors: evidence for preserved pulsatility and diurnal variation with increased secretory disorderliness. Darzy KH, Pezzoli SS, Thorner MO, Shalet SM. J Clin Endocrinol Metab. 2005 May;90(5):2794-803.

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