Plant-Based Diets and Longevity

Plant Protein

We'd die quite quickly without amino acids, the organic compounds that serve as the building blocks for every protein in the human body. Without them—and in particular the nine essential amino acids that our bodies cannot make on their own—our cells can't assemble the life-giving enzymes needed for life.

Meat contains all nine of the essential amino acids. That's easy energy, but it doesn't come without a cost. Actually, a lot of costs. So can we just avoid protein? Ironically, protein is what satiates us. Same for mice. Same for swarming locusts in need of nutrients, which is why they eat each other. ¹ It would appear that animal life can't easily limit protein in the diet without some hunger pains.

There isn't much debate on the downsides of consumption of animal protein. Study after study has demonstrated that heavily animal-based diets are associated with high cardiovascular mortality and cancer risk. Processed red meats are especially harmful. Hot dogs, sausage, ham, and bacon might be gloriously delicious, but they're ingloriously carcinogenic, according to hundreds of studies that have demonstrated a link between these foods and colorectal, pancreatic, and prostate cancer. ² Red meat also contains carnitine, which gut bacteria convert to trimethylamine N-oxide, or TMAO, a chemical that is suspected of causing heart disease.

That doesn't mean a little red meat will kill us—the diet of hunter-gatherers is a mix of plants packed with fiber and nutrients, mixed with some red meat and fish in moderation ³ —but if we're interested in a long and healthy life, our diet probably needs to look a lot more like a rabbit's lunch than a lion's dinner. When we substitute animal protein with more plant protein, studies have shown, all-cause mortality falls significantly. ⁴

Limiting Intake of Amino Acids

From an energy perspective, the good news is that there isn't a single amino acid that can't be obtained by consuming plant-based protein sources. The bad news is that, unlike most meats, weight for weight, any given plant usually delivers limited amounts of amino acids. From a vitality perspective, though, that's great news. Because a body that is in short supply of amino acids overall, or any single amino acid for a spell, is a body under the very sort of stress that engages our survival circuits.

When the enzyme known as mTOR is inhibited, it forces cells to spend less energy dividing and more energy in the process of autophagy, which recycles damaged and misfolded proteins. That act of hunkering down ends up being good for prolonged vitality in every organism we've studied. What we're coming to learn is that mTOR isn't impacted only by caloric restriction. ⁵ If we want to keep mTOR from being activated too much or too often, limiting our intake of amino acids is a good way to start, so inhibiting this particular longevity gene is really as simple as limiting our intake of meat and dairy.

It's also increasingly clear that all essential amino acids aren't equal. Rafael de Cabo at the National Institutes of Health, Richard Miller at the University of Michigan, and Jay Mitchell at Harvard Medical School have found over the years that feeding mice a diet with low levels of the amino acid methionine works particularly well to turn on their bodily defenses, to protect organs from hypoxia during surgery, and to increase healthy lifespan by 20%. ⁶ One of my former students, Dudley Lamming, who now runs a lab at the University of Wisconsin, demonstrated that methionine restriction causes obese mice to shed most of their fat—and fast. Even as the mice, which Lamming called “couch potatoes,” continued to eat as much as they wanted and shun exercise, they still lost about 70% of their fat in a month, while also lowering their blood glucose levels. ⁷

We can't live without methionine. But we can do a better job of restricting the amount of it we put into our bodies. There's a lot of methionine in beef, lamb, poultry, pork, and eggs, whereas plant proteins, in general, tend to contain low levels of that amino acid—enough to keep the light on, as it were, but not enough to let biological complacency set in.

The same is true for arginine and the three branched-chain amino acids, leucine, isoleucine, and valine, all of which can activate mTOR. Low levels of these amino acids correlate with increased lifespan ⁸ and in human studies, a decreased consumption of branched-chain amino acids has been shown to improve markers of metabolic health significantly. ⁹

We can't live without them, but most of us can definitely stand to get less of them, and we can do that by lowering our consumption of foods that many people consider to be the “good animal proteins,” chicken, fish, and eggs—particularly when those foods aren't being used to recover from physical stress or injury.

All of this might seem counterintuitive; amino acids, after all, are often considered helpful. And they can be. Leucine, for instance, is well known to boost muscle, which is why it's found in large quantities in the protein drinks that bodybuilders often chug before, during, and after workouts. But that muscle building is coming in part because leucine is activating mTOR, which essentially calls out to our body, “Times are good right now, let's disengage the survival circuit.” ¹⁰ In the long run, however, protein drinks may be preventing the mTOR pathway from providing its longevity benefits. Studies in which leucine is completely eliminated from a mouse's diet have demonstrated that just one week without this particular amino acid significantly reduces blood glucose levels, a key marker of improved health. ¹¹ So a little leucine is necessary, of course, but a little goes a long way.

All of these findings may explain why vegetarians suffer significantly lower rates of cardiovascular disease and cancer than meat eaters. ¹² The reduction of amino acids—and thus the inhibition of mTOR—isn't the only thing at play in that equation. The lower calorie content and increased polyphenols are also helpful. All of these are valid explanations for why vegetarians live longer and stay healthier. ■