Science Round-Up Seconds: Looking at Fast, Slow & Total Protein Intake Again. More Than 2g/kg Protein = Madness?

Just out: Part I of my interview with Sean Casey from CasePerformance. This part of the three-part interview includes a basic protocol that may help you get your macronutrient and energy intake right (I put an emphasis on the word "basic", here ;-).
If you have not downloaded the podcast of yesterday's installment of the SuppVersity Science Round-Up (show starts at ~70min), I suggest that you do that first, because I am not going to repeat what I have said on air already, but will be serving you a second course, instead of the seconds or a "reheated" news from yesterday. Thus listening to the show first will help you understand the relationship between the digestive speed of various proteins and the potential disadvantage of fast digesting amino acids (and proteins) in terms of the net protein retention. And to make the "news dish" even more palatable I am going to season the data and conclusions from the review I mentioned on air with some additional sources and references, as well as two recent studies on protein intake (one with a focus on the elderly).

Just in case you are missing something: Since I personally consider the other studies I did not mention yesterday boring compared to this one, I will focus solely on protein intake and postpone the interesting study snippets to tomorrow's installment of On Short Notice.

As I already mentioned yesterday, the data on protein digestion times and much of what I am going to discuss today comes from a 2006 review of the literature by Bilsborough and Mann (Bilsborough. 2006). Being what it is, namely a review, it does obviously have the downside of deriving the data from various studies. So take the exact values (specifically those in figure 1) with some of the often-cited 'healthy skepticism'. The same goes for the scientists' conclusions, of which the unquestionably most important and probably undisputed one is:
"Rapidly absorbed amino acids despite stimulating greater protein synthesis, also stimulate greater amino acid oxidation, and hence results in a lower net protein gain, than slowly absorbed protein (54). Leucine balance, a measurable endpoint for protein balance, is indicated in Figure 1, which shows slowly absorbed amino acids (~ 6 to 7 g/h), such as CAS and 2.3 g of WP repeatedly taken orally every 20 min (RPT-WP), provide significantly better protein balance than rapidly absorbed amino acids." (my emphasis in Bilsborough. 2006)
Another hypothesis, which does certainly make sense, bu is probably not going to be very popular in the fitness and boydbuilding community is invoked within the following considerations Bilsborough and Mann put on paper:
Figure 1: Protein uptake (mind the different scales on top vs. bottom) from different protein sources in g/h (Bilsborough. 2006)
"This 'slow' and 'fast' protein concept provides some clearer evidence that although human physiology may allow for rapid and increased absorption rate of  amino acids, as in the case of WP (8 to 10 g/h), this fast absorption is not strongly correlated with a 'maximal protein balance,' as incorrectly interpreted by fitness enthusiasts, athletes, and bodybuilders. Using the findings of amino acid absorption rates (using leucine balance as a measurable endpoint for protein balance), a maximal amino acid intake measured by the inhibition of proteolysis and increase in postprandial protein gain, may only be ~ 6 to 7 g/h (as described by RPT-WP, and casein), which corresponds to a maximal protein intake of 144 to 168 g/d." (my emphasis in Bilsborough. 2006)
We tend to ignore and overread things, we don't like, so let me briefly repeat the most important message here: If postprandial protein gain maxes out at 6-7g/h and the day has no more than 24h you math would tell you that eating more than 144-168g of protein per day is bogus.

"You are kiddin' me!? More than 168g/protein per day is bogus?"

Figure 2: The existing differences in fractional protein synthesis (FSR) are "biologically probably insignificant" - in other words given they have the same muscle mass sprinters, bodybuilders and even endurance athletes have the same FSR (Mittendorfer. 2006)
To support their argument that the exuberant protein intake, as it is praticed by fitness enthusiasts, athletes, and bodybuilders who have an incorrect understanding of the relation between fast absorption of proteins and "maximal protein balance" is total bogus, Bilsborough and Mann cite a previous paper by Rennie who reports that the increase in protein synthesis saturates even when amino acids are infused directly and continuously into the blood stream at ~12 g/h for an 80kg individual (Rennie. 2001).

In a similar context, Mittendorfer et al. report in a 2005 paper that the protein synthesis rates in human muscles are neither determined by anatomical location nor fiber-type composition, as the differences they observed were <15% and thus "biologically probably insignificant" (Mittendorfer. 2006). The relative increase in sarcoplasmic and myofibrillar protein synthesis were +100% and +200%, respectively (see figure 1 on the right). It may be possible that you can squeeze a little more after a workout, but let's be honest, you also got to sleep and I would hope you are not even remotely considering hooking yourself up with an AA infusion over night ;-)

"So is protein bad for me?"

Two notes on more recent studies: Deutz and Wolfe are soon going to publish an "opinion paper" in the Journal of Clinical Nutrition that's titled "Is there a maximal anabolic response to protein intake with a meal?" Their answer that it isn't is however misleading, because they are dealing with "high protein meals" of 30g and total protein intakes of 1.5g/kg (Deutz. 2012). Of much greater significance not just in the context of this individual blogpost, but also with respect to the dietary guidelines and thus public health is a paper by Volpi et al. in the Journals of Gerontology in which they demand that the guidelines for protein intake in the elderly have to be revised (Volpi. 2012). Just like me they put a much greater emphasis on the importance of hitting the threshold intake (~30g total protein) with every meal than on the total amount of protein in the diet and point out that the data from the latest NHANES study clearly suggests that older individuals reach this threshold - if anything - with dinner.
Don't get me wrong I don't want to put you off protein (both literally as well as metaphorically ;-) - but there is a physical reality out there that is full of thresholds, which are often more than just upper limits and you can hardly argue with Bilsborough and Mann as far as their conclusion with respect to physically active people and their effort to build and preserve body protein is concerned:
"Diminished reserves of TCAI through restricted carbohydrate intake [which would become necessary if you don't won't to overeat with too much carbs on top of all the protein] could potentially bring about an early onset of fatigue, decrease exercise performance, and promote muscle catabolism. As protein absorption of real foods is approximately 1 to 4 g/h, and fat is absorbed at approximately 14 to 18 g/h, the need for adequate glucose to prevent muscle gluconeogenesis and hence preserve lean muscle is important and further supports the need for a minimum carbohydrate intake, especially for active people. A carbohydrate intake of 120 to 150 g/d could be sufficient with active people consuming > 150 g/d from a large variety of cereals, whole grains, fresh fruit, and vegetables." (Bilsborough. 2006)
Actually I believe there is no additional "bottom line" necessary here (aside from picking the right "whole grains" and "cereals", of course): Protein is the building block for lean muscle tissue, but what happens on a construction site if you have plenty of building blocks, but neither electricity (carbs), nor gasoline (fats) to power the devices (let alone beer to satisfy the workers *rofl*)? Right, nothing happens! And in the end you can be happy if the part of the house that's already standing won't whither away and fall apart...

I guess among you there will be only few who still fall into the category of mislead protein worshipers, but just to make sue: 2g/kg is more than enough and my longstanding suggestion that 1.5g/kg would do as well - if it's from EAA rich protein sources, even better - still stands.

  • Bilsborough S, Mann N. A review of issues of dietary protein intake in humans. Int J Sport Nutr Exerc Metab. 2006 Apr;16(2):129-52.
  • Deutz NE, Wolfe RR. Is there a maximal anabolic response to protein intake with a meal? Clin Nutr. 2012 Dec 1.
  • Mittendorfer B, Andersen JL, Plomgaard P, Saltin B, Babraj JA, Smith K, Rennie MJ. Protein synthesis rates in human muscles: neither anatomical location nor fibre-type composition are major determinants. J Physiol. 2005 Feb 15;563(Pt 1):203-11.
  • Rennie MJ. Control of muscle protein synthesis as a result of contractile activity and amino acid availability: implications for protein requirements. Int J Sport Nutr Exerc Metab. 2001 Dec;11 Suppl:S170-6. 
  • Volpi E, Campbell WW, Dwyer JT, Johnson MA, Jensen GL, Morley JE, Wolfe RR. Is the Optimal Level of Protein Intake for Older Adults Greater Than the Recommended Dietary Allowance? J Gerontol A Biol Sci Med Sci. 2012 Nov 26.
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