Protein and Longevity

The following is an edited transcription based on the above video to provide additional context and support. 

There are few topics of greater interest than longevity–we are understandably obsessed with living long, healthy lives. Among the fruits of this obsession is the discovery and appreciation of a cellular protein signal called mTOR. mTOR has been implicated as a key protein that promotes the aging of a cell. This is largely due to its effects on autophagy. Autophagy is a process whereby a cell breaks down (to rebuild later) old parts of itself. As the cell stays functional by renewing itself, the thought is that the body by extension will be “renewed”. mTOR blocks this process–mTOR is only interested in building up the cell, not breaking it down.[1] Thus, the thinking goes that if you want a long life, you need autophagy; if you want autophagy, you need to keep mTOR turned off. And this is where diet comes in.

The idea that lowering mTOR can promote longevity is not baseless–there are ample animal studies that support this idea, but it’s not as clear as many believe it is.[2] First of all, there’s no evidence to suggest that mTOR inhibition will promote longevity in humans. It is only conjecture. But second, let’s suppose mTOR does matter. Let’s suppose that mTOR is, in fact, the protein that you want to keep turned down in the body to promote longevity.

Unfortunately, that’s a little problematic; mTOR is an essential protein that stimulates muscle and bone growth. If you want strong muscles and bones, for example, you better have frequent mTOR activation. And perhaps that’s the key to it–turning mTOR on and off, in a cyclical pattern. It’s in the dynamic cellular building up and breaking down process wherein muscles and bones get strong.

But how is mTOR turned on? The most famous method is through dietary protein, and the subsequent rush of amino acids into the blood.[3] But amino acids only elicit a temporary stimulation of mTOR, which is helpful to allow periods of autophagy after a period of building. Perhaps the problem with mTOR is when it’s turned on chronically

Interestingly, as potently as amino acids stimulate mTOR, the hormone insulin appears to have at least as dramatic an effect–activating mTOR and keeping it elevated for a longer period of time. [4] Furthermore, insulin stays higher much longer in the blood following an insulin-spiking, starchy/sugary meal than amino acids do. While amino acids usually clear the blood (and stop activating mTOR) within about 45 minutes, insulin can remain elevated for hours. And by the time insulin starts to return to fasting levels, it’s often spiked back up due to frequent eating.

These observations are relevant in light of a recently published manuscript in the British Journal of Nutrition entitled: “Diets with Higher Insulinemic Potential Are Associated with Increased Risk of Overall and Cardiovascular Disease-Specific Mortality.” The study found that people who had followed diets that increased their insulin (i.e., diets that were higher in processed starches and in carbohydrates that would give them a higher insulin level or hyperinsulinemia) had a higher mortality (i.e., chance of dying). [5] Clearly, the insulin-spiking diet wasn’t much help with living longer.

In conclusion, these sentiments challenge a broadly growing sentiment that the secret to longevity is to reduce dietary protein in the hopes of keeping mTOR turned off. If mTOR matters for longevity, all the more reason to scrutinize insulin spikes, not dietary protein.

References

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4382265/
2. https://www.karger.com/Article/Fulltext/484629
3. https://www.nature.com/articles/nrm3522
4. https://pubmed.ncbi.nlm.nih.gov/21702994/
5. https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/diets-with-higher-insulinaemic-potential-are-associated-with-increased-risk-of-overall-and-cardiovascular-diseasespecific-mortality/B938B1CE90C1A22249E44B04FBC2A3CB