Studying Methionine Restriction
The response of metabolism to lowered methionine intake appears to be a major component of the mechanisms of calorie restriction: "Methionine dietary restriction (MetR), like dietary restriction (DR), increases rodent maximum longevity. However, the mechanism responsible for the retardation of aging with MetR is still not entirely known. As DR decreases oxidative damage and mitochondrial free radical production, it is plausible to hypothesize that a decrease in oxidative stress is the mechanism for longevity extension with MetR. In the present investigation male Wistar rats were subjected to isocaloric 40% MetR during 7 weeks. It was found that 40% MetR decreases heart mitochondrial ROS production at complex I during forward electron flow, lowers oxidative damage to mitochondrial DNA and proteins, and decreases the degree of methylation of genomic DNA. ... These results indicate that methionine can be the dietary factor responsible for the decrease in mitochondrial ROS generation and oxidative stress, and likely for part of the increase in longevity, that takes place during DR. They also highlight some of the mechanisms involved in the generation of these beneficial effects."
I believe that nearly all vegan and most vegetarian diets (excluding large amounts of dairy and egg products) will be at least 40% deficient in methionine as compare to typical isocaloric American omnivore diets. It should be easy to determine whether these human diet results are similar to those in lab animals.
@ Lou Pagnucco: I know that researchers are thinking along these lines, but I'm not sure at this point how much work has been done in the form of concrete studies:
https://www.fightaging.org/archives/2009/01/revisiting-methionine-restriction-and-veganism.php
A fruitarian diet is the perfect way to restrict methionine. The real total protein requirement to maintain positive nitrogen balance is around 10g per day for the average adult. Fruits and vegetables alone provide ample protein. We are clinically evaluating an arginine and methionine restriction diet as cancer therapy. It is possible that a diet consisting of mango, pineapple, papaya, kiwi and strawberry and nothing else may be a very potent cancer treatment for early stage disease. Later stage disease may require extra help from cytotoxic agents like selenium and fatty acid synthase inhibitors like luteolin and EGCG.
A couple of other remarks -
I believe reducing the level of any essential amino acid reduces circulating IGF-1 and/or its receptors - BTW, diets deficient in the essential amino acid, tryptophan, have also increased longevity in other experiments.
The methylation issue is interesting, since some research papers claim that CR increases maintenance and de novo methylation. If MetR slows the process, does it selectively downregulate de novo methylation? Wouldn't interefering with both types lead to epigenomic instability? So what happens when both calories and methionine are restricted?
What's interesting is that vegetarians live longer than vegans, even though vegans usually have higher rates of Met restriction. Perhaps the other deficiencies in a vegan diet cancel out the Met restriction advantage.
PS @MarkSimon: A fruitarian diet is about as healthy as a high red meat diet - little real quality protein, tons of sugar. A more balanced diet is still best.
KC, where did you find your stats on vegans?
I am not suggesting a long term 100% fruitarian diet for any healthy individual. A balance with green vegetables, nuts and seeds is better. Also, B12 supplementation is essential.
For therapeutic purposes, the 100% fruitarian diet is an effective protocol for amino acid restriction. Patient compliance is another issue but most patients faced with advanced cancer that want a longer time on this earth will surrender to the diet and control food cravings.
I do not know how you an compare a red meat diet to a fruit diet. Fruits provide fiber, minerals, 2-4 percent protein, almost no fat, no cholesterol, enzymes, very high digestibility, powerful phytonutrients and no violence or suffering.
"no violence or suffering"
Maybe 'no extra violence or suffering' is a better expression. Sugar, despite being of plant origin, was an industry founded on slavery. Bananas are the very emblem of tropical plantation crops, and still are probably involved in exploitation and suffering for at least some of the workers somewhere in the world. It's hard to trace all the suffering that comes out of our actions -- eventually the effect depends on the social system as a whole, and how other people's choices affect the response to your own.
I can buy a limited argument that a raw fruit diet is nominally healthier than an all red meat diet, but mainly because there's some intrinsic variety in the family of fruits. But fundamentally these diets seem similar in kind, in that they sharply restrict the ability to include foods of complementary nutritional profiles in the diet, and in that they force you to move from relatively plausible staples to relatively wasteful eating practices. Part of the thing with fruit is that the calorie content is fairly low, so it means you will be shipping a lot of bananas from the tropics to who-knows-where to make up for that.
Just reading it frum the surface, a raw fruitarian diet seems like a slightly more sustainable version of the juice fast. That is, at least as I understand it, the calories are still coming from fruit juice except now you get the benefits of the pulp as well. I'm unconvinced that it's a good long term choice in terms of health. And like the juice fast, raw fruitarianism seems to be a breeding ground for various anti-scientific stances toward 'nutrition,' so it may have some credibility issues to work through.