A recent paper is fueling the plant-based crowd. In it, the authors found that protein restriction turned off many genetic and molecular signals of aging.
It was a synthesis of over 350 existing studies, a mix of in vitro research, animal research, and human trials, and the overall finding was that restricting protein elicited favorable levels and changes to mTOR, FGF21, oxidative stress, and other things associated with or contributory to aging.
Now, the study had some interesting things, right? There was some nuance there. They readily admitted that protein restriction acts differently in sedentary versus active individuals. Those who are actively training have a higher supposedly “safe” window of protein consumption. Maybe they have a higher tolerance for protein. But overall, the thrust of the paper, and what most people will take away from it, and what your vegan friends are no doubt bragging to you about, is that less protein is better for longevity.
I don’t think it’s as simple as that. Let me explain.
Does Eating Meat Reduce Longevity?
Much of the research rests on the assumption that specific amino acids in excess promote aging. The one they say most is methionine. It’s found in dairy, muscle meat, eggs, and other animal products, and absolutely, excessive amounts of it can promote aging in animal models, and likely humans. No argument there.
But what these studies never explore is the reality that methionine is balanced by another amino acid: glycine. Glycine is almost entirely absent from the classic animal protein products like meat or eggs or dairy, and it’s found almost exclusively in connective tissue, bones, and skin.
There is a classic study where they put rodents on a high-methionine diet, and sure enough, those rats died pretty young. But they took another group and gave them glycine, same amount of methionine, just with extra glycine, and those guys lived long, healthy lives, just as long as the rodents who lived on a restricted-methionine diet.1-2
We see echoes of this in the human literature. Tons of research finds that low glycine levels in the serum predict type 2 diabetes, heart disease, and many of the other diseases classically linked to meat consumption.
Now let’s look at Hong Kong, which is one of the longest-living populations on Earth, who also happen to eat the most meat of anyone on Earth. But the meat they’re eating is not just steaks and burgers and roasts. They’re also eating skin, snouts, feet, and other animal foods that are high in glycine.
This is why collagen is so essential for the modern meat eater who doesn’t want to eat the obscure stuff like skin and bones. Thirty to 40 grams of collagen a day provides enough glycine to balance out all the muscle meat and other animal protein you eat. And although we don’t have direct human trials of balancing out methionine with glycine and looking at lifespan, the circumstantial evidence is pretty strong that it’s going to have good effects.
Except that in the real world, when you see people who actually practice this, these are people who live this lifestyle, they’ve read the studies, they’ve convinced themselves that protein restriction is key to living long. They are generally pretty unwell. They’re frail, always cold, have low energy, and generally aren’t the picture of health we are imagining for ourselves.
Now, they may be better off and look better than the general population in some ways. They tend to be thinner, at least, and, you know, even their biomarkers look pretty good. But I refuse to believe that this is the path to optimal health. You may limp by a bit longer. You may slowly walk into old age, but can you still run hills? Can you play? Are you strong?
And that’s where the study loses me.
My Beef with the Findings
Nothing against the authors themselves. It’s pretty impossible to cover every angle, and as I said before, they did a pretty fair job of noting that active exercisers have a higher tolerance of protein. But the true path to health is on the teeter-totter, the seesaw, the waxing and the waning.
It’s a big steak after a workout and then maybe skipping breakfast the next day and just having some fish with salad for lunch. It’s periods of abundance and periods of restriction. It is high-protein days and lower-protein days. We see this everywhere. We see it in wild animals, predators who eat and gorge themselves for a day or two and then go for several days without eating anything. You see this in the fasting habits of monks and other religious men. Christianity even has protein fasting built into it.
No, I’m not saying that you should fast for three days after you eat a big steak like a tiger or wolf, or eliminate protein for a 14-day period. I’m just saying that the world is cyclical. That seems embedded in our environment and also our biology.
This is why, over the years, I have settled on not daily protein targets, but four- to five-day protein targets, even weekly protein targets. I want to eat an average of 120 grams of protein a day over the course of a week. Some days it’ll be 180, other days it’ll be 70. It doesn’t matter so much day-to-day as it does across the week.
Do studies like this give you pause, or do you remain confident—as I do—in the healthfulness of an “high” (read, “sufficient”) protein omnivorous diet? Let me know in the comments.
References
https://journals.physiology.org/doi/abs/10.1152/physrev.1970.50.3.428
https://pubmed.ncbi.nlm.nih.gov/3668700/
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* This blog reflects my personal views and opinions and isn’t intended as medical advice, but I hope it will be informative and inspiring as you pursue a healthy, fulfilling life.
I don't think you can beat the whole 'moderation' in all things. I'm with you on the average over a week or even two ... the golden mean! Days of high protein, days of low, is how our ancestors would have naturally eaten according to season and festivals etc.