The sweet spot for protein intake encompasses two goals which are at least in theory somewhat opposed to each other.
Goal 1: I want to get maximal hypertrophy from my weightlifting sessions.
Goal 2: I want to oppose the aging process, reduce disease risk, and maximize lifespan.
Why are these goals opposed to each other, at least in theory? The reason harks back to the growth-longevity tradeoff. Generally, the more an organism grows, the shorter the lifespan will be, due to the nature of mTOR and other biochemical mechanisms.
On the other hand, maximizing muscle growth from weightlifting entails eating a substantial amount of protein.
Maybe we can balance the two. Maybe it’s possible to maximize hypertrophy and retard aging at the same time. We need to find the right amount of protein, enough to maximize hypertrophy without compromising lifespan. I’m not saying that it can be done, but that’s what I’ll look at here.
Most bodybuilders will tell you that the more dietary protein you have, the better. But there are limits to how much protein the body can use. For example, a study called Evaluation of protein requirements for trained strength athletes found that for strength athletes, a diet with 1.4 grams protein per kilogram of bodyweight produced a balanced state, whereas 0.86 grams was not enough, and at 2.4 grams, some of the protein was being burned for fuel and not used for hypertrophy.
These results are broadly in line with other studies, notably the widely cited and agreed upon calculations in the review by Lemon. He increased the recommendation by two SD to cover just about everyone. So it appears that hypertrophy is maximized at about 1.8 g/kg bodyweight.
As Lemon says in his article, the debate continues, since many, many factors, such as other dietary components, training intensity, age, must be taken into account. But let’s go with 1.8 g/kg.
That’s still quite a bit of protein, more than double the RDA.
The most robust treatment for the prolongation of lifespan in virtually every animal it has been tried on is calorie restriction. Animals, such as rats, that are fed 30% or fewer calories than ad libitum fed animals can live up to 50% longer, and with better health, less disease. In essence, they stay younger longer, so this treatment doesn’t just prolong old age.
It appears that the main macronutrient responsible for the effects of calorie restriction is protein. “Many of the effects of dietary restriction (DR) on longevity and health span in model organisms have been linked to reduced protein and amino acid (AA) intake and the stimulation of specific nutrient signaling pathways.” If calories are restricted but protein is not, little to no benefit appears; if calories remain the same but protein is restricted, much or all of the same benefit appears.
This also seems to be the mechanism with methionine restriction: restriction of this one amino acid causes less protein to be synthesized.
The means by which protein restriction causes the longevity promoting effects of calorie restriction seems largely due to a decrease in levels of insulin and IGF-1, which promote growth of all kinds, including cancer. People who are deficient in IGF-1 have a very low incidence of diabetes and cancer.
If you ever read articles on bodybuilding sites, you see that bodybuilders seek to raise levels of IGF-1 in order to build muscle. Human growth hormone’s effects are mediated by an increase in IGF-1. One way they seek to raise IGF-1, other than hormones and steroids, is through increased dietary protein.
So here’s the problem: does raising IGF-1 through higher protein intake in order to maximize hypertrophy lead to a higher rate of aging and greater risk of cancer and other diseases of aging? I’d say that it does.
Can we build muscle and decrease aging? There may be a way.
Muscle growth seems to be much more linked to myostatin than it does to IGF-1. Quote: “… growth factor responses local to the muscle may be more important than circulating factors in contributing to muscle hypertrophy with resistance training.”
We don’t need large systemic increases in IGF-1 to promote hypertrophy. Therefore, at least as far as IGF-1 goes, we don’t need as much protein.
There’s some evidence that trained weightlifters and bodybuilders need less protein than beginners. Trained athletes use protein more efficiently, and beginners are packing on muscle like gangbusters, so this makes some sense.
Dedicated members of the Calorie Restriction Society who were eating ~1.7 g/kg daily of protein had IGF-1 levels of 194 ng/ml after several years of calorie restriction. That’s a high protein intake and represented, for them, about 24% of total calories. After dropping their protein intake to less than 1 g/kg for three weeks, their IGF-1 levels dropped by about 25% to 152 ng/ml. The problem with interpreting these results is whether these IGF-1 levels, both before and after dropping protein intake, are good or bad. I don’t know and don’t think anyone knows what level of IGF-1 conduces to lower mortality and longer life.
We don’t know which levels of IGF-1 are healthy and which conduce to aging. Another aspect is that IGF-1 levels are a relatively esoteric lab test that most people do not regularly get; I’ve never had one, for instance.
Would we be compromising hypertrophy from weightlifting by decreasing protein intake, or is there a sweet spot where we can have the best of both worlds: increased lifespan and robust muscle building. Again, the answer isn’t clear. I am however beginning to suspect that the bodybuilder’s standard of 1.8 grams of protein per kilogram of bodyweight daily may not be optimal for increased lifespan. Weightlifting is great, but perhaps the protein not so much.
If any readers have anything to add I’d love to hear it.
Updated: Pete (of Straightforward Fat Loss) alerted me to an article by bodybuilder Menno Henselmans called The Myth of 1 g/lb: Optimal Protein Intake for Bodybuilders. A number of studies are cited, all by recognized experts in the field, and this one is typical: Influence of protein intake and training status on nitrogen balance and lean body mass. In it, the authors state that elite bodybuilders needed only 1.05 g/kg protein daily to remain in nitrogen balance. Not only is this way below the usual cited figures, but it lends credence to what I stated above, that trained bodybuilders need less protein than beginners. Also of great interest, this figure is only slightly higher than the amount of protein that lowered IGF-1 levels in the members of the Calorie Restriction Society, cited above. If this is so, then it also shows that elite bodybuilders do not need high levels of IGF-1 in order to be who they are. (Possibly beginners do; that’s unknown at this point.)
So maybe we’ve found a sweet spot: slightly over 1 g/kg protein daily. This ought to provide plenty of support for muscle hypertrophy, assuming you’re not a beginner, and also prevent ultra-high IGF-1 levels. It comes with the caveat that we don’t really know the optimal IGF-1 level, although probably lower is better, other things being equal.
Another aspect not discussed in the original post is that of protein pulsing: one could eat plenty of protein on workout days, and less on off days, for a total of less protein. Since IGF-1 varies over a longer term, this should make for lower levels. In all of the research I’ve read on protein requirements for athletes, especially bodybuilders, never have I seen anything that addressed whether bodybuilders need this amount of protein only during the 24 to 48 hours after a workout, or always.