Is mTOR Good or Bad for Longevity?

An issue that keeps resurfacing in some online forums is the question of mTOR, which is related to the issue of how much protein we should eat and what amino acids in protein are good or bad from the perspective of life extension.

Protein is essential, and the amino acid leucine is key to our health. But too much protein, and too much leucine, are associated with the over-activation of mTOR (the growth pathway) and the under-activation of AMPK (the longevity pathway). Hundreds of studies have shown that too much mTOR activation can accelerate aging, at least in lab animals.

Switching off mTOR (by restricting leucine or protein) has been shown to increase the lifespan in several different species, including mice, yeast, worms and flies. Several researchers, including Dr. David Sinclair of Harvard Medical School and Dr. Valter Longo, Professor of Gerontology at UCLA, have cited those studies when mentioning the benefits of a low or moderate protein diet.

Most Americans eat diets that are high in all three macronutrients (fat, protein and carbohydrates). Both excess protein and excess carbs can activate mTOR and suppress AMPK. Many people go through their lives constantly nibbling and eating, which keeps mTOR on a slow burn, keeps AMPK off or subdued, and prevents autophagy (a process that removes debris from our cells).

But jumping from this knowledge to concluding that AMPK is “good” and mTOR is “bad” and should always be kept “off”, and that anything that might activate it, even in passing, is bad for longevity, strikes me as a dangerous oversimplification.

Too little mTOR activation also has several negative effects:

Too little mTOR can slow and disrupt healing.
Too little mTOR contributes to diabetes and insulin resistance.
Too little mTOR can cause specific health problems such as cataracts in mouse models.
The approaches some people use to lower their mTOR such as eating less protein can result in muscle wasting, particularly in elderly people.
None of this is to negate that there can be benefits to lowering mTOR activity. But it does not need to be low all of the time. And there can be serious health problems if it goes too low.

What about veganism?

One way of keeping mTOR in the “off” position would be to eat a vegan diet. I was vegan myself for almost three years, carefully balancing my foods to make sure I was getting enough complete protein, vitamins and minerals without eating any food from animal sources. This gave me a certain perspective on the mTOR question.

I was hoping this would improve my health, but in the long term it didn’t. After what seemed like some initial benefits, I experienced a large number of health problems, including memory and mood issues and issues with my eyesight and my teeth, which rapidly cleared up when I added eggs, dairy and meat back into my diet.

I’ve also seen sharp declines in friends of mine who gave up animal based foods thinking it would improve their health. One of them experienced a rapid progression toward frailty, memory problems and dementia. One got rail-thin and started losing her hair and having tooth problems, then later became morbidly obese. A third had cancer; was given five years to live; went low protein vegan hoping it would give him more time on Earth, and died in only four months.

I’m not saying vegan diets are bad for everyone. Some people may have the genetics to do well on them. They can have adequate protein if they’re well planned, but the protein from plants tends to be lower in quality and bioavailability than the protein from meat and other animal sources. Most vegan diets are low in leucine, which as I’ve talked about above can be a double-edged sword.

An odd side effect of the anti-mTOR “movement” in the anti-aging community is that some people have become afraid of exercising due to a fear of activating mTOR. Doug McGuff addresses these concerns, which I believe are misguided, in this video.