Investigating Optimal Protein Frequency

The Nemesis of a High-Protein Meal Has a Name - & Its Name is 'Refractory'

There are a few things in bodybuilding that are just accepted as fact; they are beyond reproach or question. We all KNOW that to optimize mass gains, it is crucial to consume adequate amounts of high-quality protein. We all KNOW that the best way to consume high protein intakes is to spread them out into small frequent meals, to keep amino acid levels elevated constantly, in order to constantly keep ourselves in a state of anabolism. We know that eight meals per day is the best way to go! We are ALL WRONG!

 How often protein should be consumed is just as important as how much should be consumed at each meal, as the summation of the anabolic response to the meal is not only how high the response peaks, but how long the response lasts. In other words, when a high-protein meal induces an increase in protein synthesis, how long does that response last and when can you stimulate it again? This will determine optimal meal frequency to maximize anabolism.
Our lab has demonstrated that the anabolic response to a complete meal containing protein, carbohydrates and fats peaks at 90 minutes and returns to baseline by 3 hours.1 So that makes it easy, right? We should just eat every 3 hours. Well, before you go running off with this information, read the rest of what I have to say. What is REALLY interesting about our findings is that while protein synthesis had returned to baseline after 3 hours, plasma amino acid levels were still elevated above baseline and plasma leucine (the amino acid responsible for increasing protein synthesis) was elevated almost 3x above baseline!

Accordingly, the activation of the mTOR pathway (mTOR activation initiates protein synthesis) was still maximized at 3 hours, whereas protein synthesis had returned to baseline. Thus, increases in plasma leucine were able to trigger mTOR signaling and protein synthesis, but sustained elevations of plasma leucine and mTOR signaling were not sufficient to maintain elevated protein synthesis. This suggests a ‘refractory’ response of protein synthesis to prolonged elevations in plasma amino acids. Bohe et al. also demonstrated the refractory response to constant elevations in amino acids during a 6-hour infusion of essential amino acids.2 The infusion produced constant elevations in plasma EAAs; however, protein synthesis lasted only 2 hours and could not be further stimulated during the 6-hour period.

It is unlikely that eating another meal 2-3 hours after the first meal would be sufficient to increase protein synthesis again, since amino acid levels are already elevated. Therefore, in order to avoid refractoriness and maximize anabolism, it may be best to consume larger doses of protein to maximize protein synthesis, while allowing enough time (4-6 hours) for amino acid levels to fall between meals, in order to resensitize the system.

Now I’ve probably shocked you so much that you spit your protein shake out all over your magazine and now you are cursing me for 1) ruining your new issue of MD, and 2) telling you the bodybuilding meal-eating protocol you’ve been following for so long may not be optimal for making gains! You worked so hard for so long, to ensure that you were always getting a constant level of amino acids in and now you’re being told that this refractory jerk is saying all your efforts are for naught! Well, I apologize for ruining your magazine, but I won’t apologize for busting on musclehead dogma— that is just what I do.

One possible mechanism to explain refractoriness (it really is a word, I checked), is that there is a membrane-bound protein stat, either extracellular or intracellular, which is sensitive to relative CHANGES in amino acid concentrations, rather than absolute concentrations. In this case, producing constant elevations in plasma amino acids would produce a refractory response, as an unchanging elevation in amino acids would not be sufficient to activate the protein. One possible way to overcome this would be to consume a sizable dose of free-form amino acids in between meals to produce a rapid supraphysiological increase in plasma amino acids, which would also quickly decrease, to re-sensitize the system.

Another possible explanation for refractoriness may involve insulin. The time course of plasma insulin in our study seemed to track protein synthesis.1 Bohe et al. also showed a similar pattern during their infusion study.2 While increasing insulin is not required to initiate protein synthesis, it does maximize the anabolic response to amino acids.3,4 Perhaps elevations in plasma insulin are required to MAINTAIN protein synthesis after a meal. If this is true, it is likely that the mechanism is independent of insulin’s effects on the mTOR pathway, as our lab demonstrated that the refractory response can occur even when mTOR signaling remains elevated.1 While insulin is not required to initiate protein synthesis, it is known to stimulate peptide elongation (the elongation of a growing protein as it is synthesized) in skeletal muscle.5 If declining plasma insulin concentrations reduce peptide elongation, it could possibly ‘short-circuit’ protein synthesis and explain refractoriness.

 Consistent with both of these theories, Paddon-Jones et al. fed three high-protein meals, spaced 5 hours apart, with or without a 15-gram essential amino acid/30-gram carbohydrate supplement in between each meal and measured the anabolic response to each treatment.6 They found that over the course of the day, the group that consumed the supplement had a greater anabolic response than the group that did not receive the supplement. Perhaps consumption of the free-form amino acid supplement along with carbohydrate was sufficient to overcome the refractory response, or the supplement merely optimized the anabolic response to each meal.  
 In either case, it appears that consuming larger doses of protein spaced further apart (4-6 hours), while supplementing with a free-form amino acid and carbohydrate supplement between meals, is an effective way to maximize muscle protein synthesis and possibly overcome the refractory response.

References:
1. Norton LE, Layman DK, Garlick PJ, Brana DV, Anthony TG, Zhao L, Devkota S, and Walker DA. Translational controls of muscle protein synthesis are delayed and prolonged associated with ingestion of a complete meal. FASEB J, 2007 21: 694.6 [Meeting Abstract]
2. Bohe J, Low JF, Wolfe RR, Rennie MJ. Latency and duration of stimulation of human muscle protein synthesis during continuous infusion of amino acids. J Physiol, 2001 Apr 15; 532(Pt 2):575-9.
3. Anthony JC, Lang CH, Crozier SJ, Anthony TG, MacLean DA, Kimball SR, Jefferson LS. Contribution of insulin to the translational control of protein synthesis in skeletal muscle by leucine. Am J Physiol Endocrinol Metab, 2002 May; 282(5):E1092-101.
4. Greiwe JS, Kwon G, McDaniel ML, Semenkovich CF. Leucine and insulin activate p70 S6 kinase through different pathways in human skeletal muscle. Am J Physiol Endocrinol Metab, 2001 Sep; 281(3):E466-71.
5. Yoshizawa F, Tonouchi A, Miura Y, Yagasaki K, Funabiki R. Insulin-stimulated polypeptide chain elongation in the soleus muscle of mice. Biosci Biotechnol Biochem, 1995 Feb; 59(2):348-9.
6. Paddon-Jones D, Sheffield-Moore M, Aarsland A, Wolfe RR, Ferrando AA. Exogenous amino acids stimulate human muscle anabolism without interfering with the response to mixed meal ingestion. Am J Physiol Endocrinol Metab, 2005 Apr; 288(4):E761-7. Epub 2004 Nov 30.