Valid point about methionine restriction. I didn't mean to come across as making authoritative claims. I am simply cautioning people against jumping into dietary changes that would cause them more harm than good.

First things first, different groups of humans have different protein requirements (pregnant women, elderly, athletes, sedentary non-active adults etc) so generalizations in nutrition science are always dangerous.

Secondly, the studies you cited have been experimental on yeast and mice, but observational and correlational with humans - nothing conclusive about how a practical reduction in methionine and leucine in the real world for real humans would work, and how it would affect them long term. Those are two completely different scenarios, with the former being highly controlled studies of non-human species.

Thirdly, even if methionine reduction did positively affect lifespan/healthspan, the reality is that most people are simply not equipped to take on such a dietary change, leading to more harm done than good.

The reality is that, yes, many animal foods contain much more methionine than plant based. However, you also have to consider that if regular people tried to switch to plant-based (aside from lacking general education about plant-based diets), in order for them to consume sufficient amounts of protein from plants, they'd end up consuming a lot more calories (not only fibre but other simpler carbs) due to the higher calorie-to-protein ratio. This, especially if they don't live very active lives, would contribute to weight gain, all the while them thinking they're being healthier by being plant-based.

I understand that these are promising studies that have been around for a while, and I was a vegetarian for 5 years before switching back to omnivore due to becoming more disillusioned by the vegetarian diet, especially as I was trying to build muscle while on veggie+fasting, and failing.

But context matters, real world conditions matter.

Correlational/observational studies don't mean shit because they cannot possibly account for the diverse lifestyle practices of the participants living in the real world, try as they might.

Hence why I'm advocating for people to simply consume more protein, because, even though there might be benefits to restricting certain AAs, a lot of other implications to this dietary change might be overlooked, causing more harm to the health long term.

Let me know if I'm missing something crucial.

> nothing conclusive

It's true that conclusive lifelong human trials with appropriate controls are not available; but neither will they be, they're impractical.

The mechanistic basis for the health benefits of protein restriction is established to be conserved across species; they key aspects are mTor suppression, reduced IGF-1 levels and a shift from anabolic hypertrophy to catabolic autophagy.

This now famous study [1] showed that people in a large cohort who shifted to plant foods did manage to achieve lower mortality rates, perhaps challenging your assumption about the ability of the "regular person" to plan an effective diet that restricts protein.

In contrast to your experience, I am obtaining all micronutrients on a plant-based, whole foods diet, at under 1.5kcal/day; I drink one pea protein shake, for a total of 1.4 * bw. I'm happy with this, it's a form of "dietary restriction with optimal nutrition", but I'm not looking to increase muscle mass, because anabolic hypertrophy is detrimental to my longevity goals. I do exercise regularly and strength continues to increase, albeit modestly; this is consistent with a recent human trial that showed dietary restriction can lead to loss of muscle mass, yet without loss of strength.

[1] https://pubmed.ncbi.nlm.nih.gov/27479196/

Thanks for elaborating. I hope you're right, and after I'm finished with hypertrophy I'll try to tip the balance more in the direction of plant-based again. Cheers.