Jain can drink milk and eat dairies, which are a good source of B12.

One of the major criticisms of a vegan diet is the a almost complete lack of B12.

> when there are whole civilizations that exist on a diet, you will be okay.

If okay = "survive long enough to leave offspring", then yes. However, health and quality of life are a lot more complicated than survival, that's why we look deeper into the science instead of using these rules of thumb.

A truly vegan society would eventually go extinct if they didn't supplement with B12. To my knowledge, this isn't possible without modern technology.

It can take many years for freshly minted vegans to have their stores of essential nutrients depleted, so they may in fact reproduce successfully for one generation, but in the long run severe malnutrition is inevitable.

Okay = survive long enough to leave offsprung, and be strong enough not to be murdered by your neighbours.

Of course there is more to healthiness thsn that and science is important, but as far the rule of thumb goes, the second part is important.

To my knowledge, there is not a single tribe known to survive on a truly vegan diet for any extended period of time (several generations).

Jains are generally vegetarians, not vegans. There may be some anecdotes that some Jains did live off truly vegan diets, but then again there are anecdotes of people living off sunshine. Neither are plausible.

Counterpoint: there's a whole civilization on the western/USA diet, which has been shown to not be that great for your health (see e.g. obesity rates).

Counterpoint to your counterpoint, there are also whole civilizations in the Western world, for ex, the peoples of Southern Europe (France, Spain, Italy, Greece) who are total omnivores and boast some of the highest life expectancy rates in the whole world. They don't eat a magical "Mediterranean" diet or other such nonsense: most people will eat a wide variety of things, from vegetables, to fatty processed foods like cheese and sausage.

My point is I don't think there is a single "Western" diet with distinct health outcomes (just like the "Mediterranean" diet is also a myth).

You are gladly ignoring lots of differences in the diet between Southern Europe and the US. From the size of portions, to the prevalence to HFCS in the American diet, the dramatic difference in consumption of things like olive oil, wine, or beer , the consumption of soft drinks with the main meals of the day, etc. Americans consume signifcantly more Coca Cola than say the Italians, Spaniards or French. Guess what happens then?

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3828681/

> Results. Soft drink consumption increased globally from 9.5 gallons per person per year in 1997 to 11.4 gallons in 2010. A 1% rise in soft drink consumption was associated with an additional 4.8 overweight adults per 100 (adjusted B; 95% confidence interval [CI] = 3.1, 6.5), 2.3 obese adults per 100 (95% CI = 1.1, 3.5), and 0.3 adults with diabetes per 100 (95% CI = 0.1, 0.8). These findings remained robust in low- and middle-income countries.

I’m not, I’m well aware that around these parts they don’t sell gallon-buckets of soda in gas stations...

I was just pointing out how you mentioned “Western” diet, but I don’t think that’s a thing.

Jainism is completely different to veganism, so unsure what point you’re trying to make here.

Jainas are not necessarily vegans.

Although the nation of India checks out for vegetarianism. One wonders what that collective moment of culture was that a whole group of people decided that meat eating was not going to be a part of their lifestyle.

The usual reason behind being vegeterianism in india is mostly spiritual or family tradition.

Giving up Tamas food (meat, garlic, onion etc.,) is the first set of rules to follow on a spiritual journey.

once a family starts on this path, the behavior permeates to next generation automatically.

even though my family allowed me to eat meat, i started & stopped within a year because of ethical reasons (and not spiritual reasons).

Using such rule of thumb would let one believe that cannibalism is ok as part of diet because Fore people practised it for generations. We of course know now that it caused spread of Creutzfeldt-Jakob disease among them with incubation period on average longer than 10 years. There even appeared mutation among them which granted immunity to it.

What a bizarre and irrelevant thing to say.

Cannibalism, nutritionally speaking, is perfectly healthy, if you stick to muscle meats. Eating the brain of prion-infested sheep can kill you just as thoroughly as the brain of prion-infested humans.

We don't practice cannibalism for other reasons...

False equivalency. If you eat brain of prion-infested sheep, it will end with your death. With cannibalism it continues after members of your community eat you at your funeral, that allows for much wider spread of the disease. We don't practice cannibalism because of our own cultural norms, but that doesn't mean there aren't other good reasons for not doing it. (And question is whether out cultural norms against cannibalism didn't develop just to save us from this, after all there are speculations that it was kuru-like disease that caused extinction of Neanderthals[1])

[1]: doi:10.3390/pathogens2030472

Cannibalism was widespread well into historical times.

And it's quite possible that this was a reason why it stopped.

No it isn't.

quite the opposite diet can be claimed by the inuit. more, the most powerful civilization in the world, the US, has objectively one of the worst diets in history.

"more, the most powerful civilization in the world, the US, has objectively one of the worst diets in history."

The diets in the US have gotten worse in recent decades (way more processed foods especially) and the US is objectively facing the ramifications of those diets. That doesn't make them any less powerful but this discussion was actually about health and I think in this regard it paints a clear picture that this is not the way to go.