Ugh, protein discussion again? Yes! Here we go!
If you have been reading the forums here for awhile, then you probably have come to realize that the US RDA for protein (0.8 grams per kg bodyweight per day) is woefully inadequate for all athetes, and specifically too low for people engaged in regular weight training.
Now, assuming you already know the basics, I would like to discuss fact-based information regarding very-high protein intake during caloric deficit for those of us that have been consistently weight training beyond the beginner stage and are relatively healthy (no pre-existing kidney problems or any medical reason to avoid high protein intake).
Anecdotally, many bodybuilders will increase protein intake well above 2.2 g/kg total bodyweight, especially during a weight-loss phase before competetion, as it has been shown that high protein intake promotes lean mass retention during caloric deficit. However, data from studying bodybuilders is often skewed by drug-assisted results that just do not pertain to drug-free natural lifters, as it has also been shown that drug-assisted athletes have higher protein synthesis capabilities. So, hopefully, this thread can stick to facts that exclude drug-assisted athletes. Also, please keep protein intake discussion here limited to grams per kilogram of bodyweight per day (g/kg/d) if possible, because that is the standard that you will see in the scientific literature.
Although this discussion is intended for highly-trained lifters, who probably already have a good knowledge of nutrition, I think it is useful to look at some history to see how protein recommendations have evolved, and hopefully gain some insight into where research may be headed in the future.
Most of the older research I have seen on the subject focuses primarily on the metric of nitrogen balance. Methodically, protein intake is increased until N into the body = N out, showing that an equilibrium point exists where nitrogen uptake by the body has been saturated.
The most-cited of these older studies is the 1988 Walberg et al. study (http://www.ncbi.nlm.nih.gov/pubmed/3182156
) which showed a 1.6 g/kg group in positive nitrogen balance and the 0.8 g/kg group having a negative nitrogen balance. The lower protein group lost more lean body mass, and although the difference was not statistically significant, it was only a one-week study. Later research like the 1998 Lemon paper (http://www.ncbi.nlm.nih.gov/pubmed/9841962
) settled on a 1.6-1.7 g/kg result being the best choice for strength athletes to maintain positive nitrogen balance.
It later became clear that nitrogen balance is just one piece of the puzzle, especially during caloric deficit (http://www.bodybuilding.com/fun/planet4.htm
). A nice criticism of these older studies, and very-high protein intake in general, is provide by Henselmans:
However, I find his arguments that 1.8 g/kg is sufficient for LBM retention during deficit to be somewhat tenuous here, since he only references the above Walberg study (which was only one week long and did not have a very-high protein group above 1.8 g/kg) and a 2008 Pikosky et al. study (http://www.ncbi.nlm.nih.gov/pubmed/18379214
) which makes no mention of the weight-training history of the participants, noting only that they were already "healthy" and "physically fit", and had at least a 6 month history of endurance training. As noted in Lemon 1998 above, endurance athletes have lower protein intake requirements than weight-training athletes.
When protein intake goes higher than nitrogen equilibrium (where clearly protein synthesis is already maximized), is there any benefit to the experienced, natural weight lifter during caloric deficit?
Many of the more modern studies compare high protein to low protein (near US RDA levels), like this 2010 from Mettler et al. that shows a clear benefit from 2.3 g/kg compared to 1.0 g/kg:
The problem with this is that we already know that higher is better than US RDA, but how high should we go? We also now have plenty of papers like the 2011 Phillips and Loon paper (http://www.ncbi.nlm.nih.gov/pubmed/22150425
) which projects 1.8-2.7 g/kg may be helpful to prevent lean mass loss. Some of today's top nutrition experts in the field recommend even higher for very lean individuals doing intense training:
2.3-3.1 g/kg (of lean body mass): http://jissn.biomedcentral.com/articles/10.1186/1550-2783-11-20
2-3 g/kg (of target bodyweight): [Alan Aragon's Research Review, Jan. 2011]
2.2-3.3 g/kg: http://www.bodyrecomposition.com/fat-loss/protein-intake-while-dieting-qa.html/
Up to 4 g/kg not specifically recommended, but considered safe: http://www.lookgreatnaked.com/blog/high-protein-intake-myths-and-misconceptions-about-saftey-part-1/
2.0-2.5 g/kg, possibly beneficial up to 3.5 g/kg: http://www.leanbodiesconsulting.com/articles/the-protein-interview-an-interview-with-dr-stuart-phillips/
However, the high end of these recommendations are mostly based on observational experience, projections and interpretations of the existing data. Very-high protein intakes remain rarely studied via proper experiment. I would like to see more very-high versus moderately-high protein studies, which feed the moderately-high protein control group in the 1.8 g/kg to 2.2 g/kg range. Unfortunately, there are not a lot of them out there that I can find.
A recent literature review from Helms et al. (http://www.ncbi.nlm.nih.gov/pubmed/24092765
) recommends up to 3.1 g/kg (of FFM) for very lean individuals in high caloric deficit. We then got a 2015 follow-up study from Helms et al. (http://www.ncbi.nlm.nih.gov/pubmed/25028958
), which showed that 2.8 g/kg failed to outperform 1.6 g/kg, except in psychological and perceived fatigue assessments. Unfortunately, this study was only two weeks long, and used caliper measurements for body composition analysis. These two papers have an excellent rebuttal from Henselmans here: http://bayesianbodybuilding.com/eric-helms-protein/
How about longer time periods? We have some interesting results from a 2014 Antonio et al. study (http://jissn.biomedcentral.com/articles/10.1186/1550-2783-11-19
), which compared 4.4 g/kg versus 1.8 g/kg over 8 weeks. Unfortunately, it is a maintenance study, not a deficit study, but a notable conclusion was reached here. The very-high protein group added a mean 145 grams of protein per day to their diet above the control group (800 additional calories over normal maintenance diet for the very-high protein group), yet both groups maintained the same LBM and fat mass over the experiment, so the authors conclude that overfeeding the hypercaloric very-high protein diet does not result in an increase in fat mass nor fat-free mass. Additionally, the very-high protein group experienced a better body composition change than the control (change in FFM/FM), although these results were not statistically significant. The authors attribute the lack of significant body weight gain in the very-high protein group to thermic effect, although this was not verified. A critical analysis of the study by Schoenfeld is posted here: http://www.lookgreatnaked.com/blog/new-study-on-protein-overfeeding-a-critical-analysis/
Antonio et al. did a follow-up 2015 investigation that compared 2.3 g/kg versus 3.4 g/kg using a structured strength program (http://jissn.biomedcentral.com/articles/10.1186/s12970-015-0100-0
). Again, the moderate-protein group continued their normal diet, while the high-protein group added additional protein to their normal diet. Both groups added FFM and lost FM, so again a maintenance diet. However, body composition results achieved statistical significance this time, with the high-protein group losing significantly more fat mass and more percent body fat than the moderate-protein group. This is in spite of the high-protein group adding almost 400 calories of protein to their baseline normal maintenance diet. The authors speculate that in addition to thermic effect, changes in AEE and NEAT may account for the significant fat loss in the high-protein group. They also note significant individual subject response variability in the results, possibly due to genetic components.
Antonio et al. just recently published another 2015 study that was similar to the 2014 maintenance study, but this one used a 16-week crossover trial (http://jissn.biomedcentral.com/articles/10.1186/s12970-016-0114-2
). Again, normal, habitual diet for the 2.6 g/kg moderate-protein phase, with only protein intake raised to 3.3 g/kg for the high-protein phase. Although the high-protein phase saw subjects lose more fat mass, statiscal significance in body composition markers was not reached. No significant body compostion changes were found between phases, despite the high-protein segment consuming an additional 450 calories over baseline. The authors note that 9 out of 11 subjects lost fat mass during the high-protein phase. They also note that the subjects averaged ~3 g/kg protein intake over the 16 week experiment, and there were no changes in blood lipids, renal or hepatic functions.
It is not clear from the current research available that there is a predictable benefit to protein intake above 2.2 g/kg for the highly-trained weight lifter during caloric deficit. While some studies show potential body composition benefits, the results often do not reach statistical significance, with high degrees of individual subject response variability usually a factor. Recent results from Antonio et al. suggest that if all other factors are controlled during maintenance diet, then it is difficult to overfeed on protein in practice, and protein overfeeding in such circumstances can actually lead to fat loss for some individuals (thereby leading to a potential slow fat-loss strategy).
So MFP, what do you think is the "optimal" protein intake for the drug-free, highly-trained weight lifter during caloric deficit? If you can find any more very-high protein intake related info, please post here.