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This recent review, noting that “vegan diets,” in part because they tend to be naturally low in methionine, “may prove to be a useful nutritional strategy in cancer growth control,” also looked at “methionine restriction” and “life-span extension.” It seems that the less methionine there is in body tissues, the longer different animals tend to live. But, what are the “possible implications for humans?”

I’ve talked before about the “free radical theory of aging”—this concept that aging can be thought of as the oxidation of our bodies, just like rust is the oxidation of metal. And, methionine is thought to have a “pro-oxidant effect.” So, the thinking is that lower methionine intake leads to less free radical production—the so-called “reactive oxygen species,” which slows the rate of DNA damage, which then would slow the rate of DNA mutation, slowing the rate of aging and disease—thereby potentially increasing our lifespan.

There are three ways to lower methionine intake: caloric restriction (they call it dietary restriction here); meaning, like, you cut your intake of food in half—for example, only eating every other day. That would lower your methionine intake. Or, because methionine is found concentrated in certain proteins, you could practice protein restriction across the board—eating a relatively protein-deficient diet. Or, the third option is to eat enough food; eat enough protein—but, just eat plant proteins, because they are relatively low in methionine.

Caloric restriction is hard, because you walk around starving all the time. Something like every-other-day eating “is never likely to gain much popularity as a pro-longevity strategy for humans.” So, “it may be more feasible to achieve moderate methionine restriction, in light of the fact that [plant-based] diets tend to be relatively low in this amino acid.” As we’ve seen, “plant [products]…tend to be lower in methionine than animal [products] .”

Yes, protein restriction across the board can be performed to avoid the hunger of caloric restriction. But, again, methionine restriction “could also be performed emphasizing low-methionine, high-quality vegetable sources of protein. Among foods containing [plant] proteins, [legumes] are especially rich in essential aminoacids, offering excellent substitutes for proteins of animal origin.”

The fact that beans have comparatively low methionine has been “classically considered…[a] disadvantage.” But, given “the capacity of [methionine restriction] to decrease the rate of [free radical] generation in internal organs, to lower markers of chronic disease, and to increase maximum longevity, ironically converts such ‘disadvantage’ into a strong advantage and [it] fits well with the important role of [beans] in healthy diets like the [traditional] Mediterranean diet. Interestingly, [soy] protein is also especially poor in methionine, and it is widely considered that [soy]-containing foods have healthy effects in human beings.”

Now, on a population level, folks could benefit from just lowering their protein intake, period. “The mean intake of proteins (and thus methionine) of Western human populations is much higher than needed. Therefore, decreasing such levels…has a great potential to lower tissue oxidative stress and to increase healthy life span in humans while avoiding the possible undesirable effects of [caloric restriction].” We’re eating “twice as much protein” as we need, so the first thing we can recommend is just “decreasing the intake of protein…has…a large potential to bring health benefits.” But then, we can lower methionine even further, eating a plant-based diet.

“The reason [plant-based diets] are [so] protective is not known.” Yes, “vegetables contain thousands of phytochemicals,” but “separately investigating their possible protective role[s would be] an impossible task. The idea that the protective effect is not due to any of the [individual plant food] components, but to a [synergistic] ‘combined effect’ is gaining acceptance… However, based on the relationship of excess dietary methionine with toxicity to major vital organs, and its likely mechanism of action through increases in [free radical] generation, the possibility exists that the protective effects of [plant-based] diets can be due, at least in part, to their lower methionine content.”

This is not a new idea. It was proposed back in 2009, but is only now gaining increasing acceptance in more mainstream scientific circles. The idea that “low-methionine content of vegan diets may make methionine restriction feasible as a life extension strategy.”

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