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Comment by nradov | Hacker News Reader

Caloric restriction has never been shown to increase lifespan in large primates. And the experiments showing increased lifespan in lower animals have been highly artificial with the subjects protected from infections and injuries. Caloric restriction in elderly people causes sarcopenia, which greatly increases the risk of disabling orthopedic injuries.

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I wonder if some of the benefits come not from caloric restriction itself but reduction of something else that's harmful.

> Regenerative healing also requires freedom from substances that inhibit the digestion of the debris. The great decline in proteolytic autophagy that occurs with aging (Del Roso, et al., 2003) can be reduced by inhibiting the release of fatty acids. This effect is additive to the antiaging effects of calorie restriction, suggesting that it is largely the decrease of dietary fats that makes calorie restriction effective (Donati, et al., 2004, 2008)[0]

[0] https://raypeat.com/articles/articles/regeneration-degenerat...

While most experiments done until now have investigated the effect of calorie restriction, there have also been some more specific experiments.

Some experiments have obtained similar lifespan extension by protein intake restriction, not by energy intake restriction. A few other experiments have obtained the same effect by restricting only the methionine intake.

Methionine is required for the initiation of the synthesis of any protein. When it is insufficient, the rate of protein synthesis slows down everywhere in the body.

Assuming that all these experimental results are correct and that they have a more general applicability than for the few tested animals, then it appears that the lifespan extension is achieved by slowing down the rate of protein synthesis.

This might work by preventing an unnecessary recycling of the body components, which eventually accumulates defects. Nevertheless, in the case of injuries or illness, a reduced rate of protein synthesis is very undesirable.

It is likely that in big or long-lived animals the rate of protein synthesis is already diminished and close to the minimum acceptable, because such animals have lower energy intake per mass needs (even when comparing poikilotherms).

This would explain why such lifespan extension methods do not seem to work in big animals. It is likely that they have low or no effect in humans too.

There are aboriginal people with a diet low in protein like New Guinea highlanders who subsides mostly on sweet potato and other starchy vegetables. Their protein intake is like 35-40 grams/day, https://pubmed.ncbi.nlm.nih.gov/7328441/

Yet they are not known for a particularly long life span. One can argue as aboriginal people they do not have access to modern medicine and most people die from preventable diseases. Yet it does allow to doubt that just by protein restrictions one can noticeably prolong life in humans.

Also their dies is low in fats, so again, this makes one skeptical towards claims that low-fat diet prolongs life.

I wonder if there's a benefit to eating precisely the amount of calories needed to prevent notable muscle loss with as little surplus as possible, or to CR in the young that you stop when you're older?

It's very difficult for elderly people to build and maintain lean muscle mass because the endocrine and digestive systems become less effective with age. After about age 70, progressive muscle loss is unavoidable (at least without heavy use of performance enhancing drugs which cause other negative side effects). So, if you want to live a long life without falling down the stairs and breaking a hip when you're 80 then you need to build up some extra muscle when you're young. That means eating a relatively high protein diet (but not a caloric surplus unless you're underweight).

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