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"A new review article discusses whether there is a maximal anabolic threshold to dietary protein.
TDLR:
- I disagree with most points in this review
- bottom of this post has better recommendations and references to read on protein intake.
Summary or review:
1) It is often recommended that 20-25 g protein nearly maximizes the muscle protein synthetic response to a meal
2) The authors suggest that in addition to effects on muscle protein synthesis, effects on muscle protein breakdown or whole-protein breakdown should be taken into account
3) The authors suggest that increasing doses of protein will augment greater reductions in (muscle) protein breakdown.
4) The authors suggest that mixed meals may result in a greater anabolic response compared to isolated protein, because insulin may reduce muscle protein breakdown
5) The authors suggest protein distribution does not matter much
I disagree with most points in this review.
Regarding point 1)
I agree with those recommendations, but keep in mind that 40 g protein typically gives a 10-20% higher MPS response and may be especially important following whole-body resistance exercise and before sleep (1, 2).
Regarding point 2, 3 and 4)
I agree with the authors that the total anabolic response is what matters. In the case of the muscle that is the muscle protein balance (synthesis minus breakdown). However, changes in protein balance are largely driven by changes in muscle protein synthesis, as protein breakdown doesn't change much and is very predictable in most conditions in athletes. Measuring it is a waste of valuable research money in many situations.
The amount of protein recommended to optimize muscle protein synthesis (20-40 g) is also enough to also minimize muscle protein breakdown. The effect of protein on muscle protein breakdown is in fact due to insulin, and you don't need that much insulin to minimize muscle protein breakdown (3). Protein alone is enough, no need for extra carbs/mixed meals to minimize muscle protein breakdown (4). Insulin/carbs are also not needed for muscle protein synthesis.
The authors suggest that WHOLE-BODY protein breakdown will be reduced further with greater doses of protein. Key words there are WHOLE-BODY. This is a measurement that is not specific to the muscle and is more reflective of what is happening in gut tissues. I know whole-body protein may sound even more important than a measurement that just looks at the muscle, but it in the opposite (unless you want to grow gut tissue?). A simple example to show that whole-body protein metabolism and muscle protein synthesis should not be confused: resistance exercise stimulates muscle protein synthesis, but not whole-body protein synthesis (5).
The authors did a study in which WHOLE-BODY protein breakdown was reduced further with 70 g protein in a meal compared to 40 g (6). Again, this does not mean it is helpful for the muscle! It does not even mean it's helpful for other tissues, we have no idea if a greater protein balance in gut tissues is even beneficial. Moreover, the methodology of that paper is questionable. Our lab gets completely opposite results with better methodology.
So the arguments of the authors that higher doses of protein might be beneficial are very questionable. There is no data that doses higher than 30 g protein would beneficial for muscle protein breakdown, and all evidence suggests that it likely would not be. Making protein recommendations for muscle mass gains/maintenance based on WHOLE-BODY protein metabolism data is also very questionable, especially since it's largely based on the results of a specific study which itself is questionable.
Regarding point 5:
I do think there is some value to protein distribution, though total daily protein intake is definitely a higher priority.
I don't have a major issue with people seeing little to no benefit in protein distribution, there is no super-compelling evidence that you leave massive amounts of gains on the table if you don't pay attention to it (though I think it's pretty simple to do? But that's up to the individual)
What I do take issue with is that they seem quite biased. For example, they wrote:
''In a recent acute metabolic study we did not observed any beneficial effects of distributing the same amount of dietary protein equally over three daily meals as compared to the normal American pattern of 65% of dietary protein with dinner as evaluated by measurement of whole body protein synthesis and breakdown as well as MPS [18]. The lack of impact of distribution of dietary protein was evident at two levels of dietary protein intake.''
When you actually look at the data from that study (see picture attached), it appears that the even protein distribution did better than the uneven protein. The effect was not statistically significant, but that most likely has to do with the study being underpowered since the exact same positive effect was found in both the lower and higher protein diet. If you would compare the evenly distributed low protein intake with the uneven distributed high protein intake, there would also be no significant difference. So you could argue that improving the distribution is as effective as doubling the amount of protein (again, this is a statistical issue). If anything, I would consider that study evidence for protein distribution. Taking the more conservative approach is fine of course. But in that case, it is inconsistent that the authors are conservative in this area, but are extremely aggressive about making protein recommendations on whole-body data?
Unfortunately, I have to admit I don't like this review. The last time these authors wrote a similar review, it was posted a lot on social media by bro's as 'SEE MORE PROTEIN!!!!!!!'. Please don't be a bro. And while I love protein, this particular review is not the reason why protein is awesome or a good reason to eat loads of it (but I still recommend to eat loads of it 😉
The authors of this review will come visit our lab next month, so we have some discussion points!
Review:
https://www.ncbi.nlm.nih.gov/pubmed/28807333
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If you just want some simple protein recommendations, a good evidence-based starting point would be the 1.6 g/kg/d suggested maximizing muscle hypertrophy in a recent meta-analysis - and perhaps up to 2.2 g/kg/d to take a safety margin (7).
Want to know more about protein metabolism, but get confused by all the methodology or can't get all the papers? Start here:
http://www.nutritiontactics.com/meas...-protein-syn…/
References:
1)
https://www.ncbi.nlm.nih.gov/pubmed/27511985
2)
https://www.ncbi.nlm.nih.gov/pubmed/27916799
3)
https://www.ncbi.nlm.nih.gov/pubmed/18577697
4)
https://www.ncbi.nlm.nih.gov/pubmed/21131864
5)
https://www.ncbi.nlm.nih.gov/pubmed/27643743
6)
https://www.ncbi.nlm.nih.gov/pubmed/?term=26530155
7)
https://www.ncbi.nlm.nih.gov/pubmed/28698222
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