There are lots of healthy lifetime vegans and omnivores though. Most of the healthy people aren’t carnivores - as there are too few carnivores but way more healthy people. Not like “healthy” is some exact thing but still, we can work with it.
I definitely feel about as healthy as after decades with almost no meat (okay, that’s almost now :D) so I don’t think meat is particularly important for me if I get my nutrients elsewhere. I mostly eat meat because it turned out I am even more okay with extreme low-carb so meat is a must.
My SO would suffer on a woe with much meat or low-carb, it seems (it’s not like he can try it for a long time but there are hints). I expect he will be quite healthy at 110 years old after his life long HCHF woe but we will see. He is very young still, not even 42, of course he had no health problem yet (except the lack of his spleen) though most people aren’t like him. Humans are horribly sickly! But genes play a huge role too. Good genes, good lifestyle, the right woe for us, all should be right for our planned very long, very healthy life. We can’t afford to make an important factor wrong.
Corals has right, there are many factors, it’s not just eating plants or not. But that may be an important factor as well. Much plants would be a problem for me (and not at all for my SO, apparently), it’s mostly an indirect effect though, adding plants make way more important changes to my woe.
But our case is just a very early N=2 so it’s insignificant (except for ourselves when we make our decisions for ourselves). We have much data, lots of people are strong and healthy as a vegan so it’s possible. Many are sick, sure, it’s easy to do it wrong, after all and it’s not good for everyone. I probably could survive without big health problems but I would be miserable on my super low-carb plant-based woe, yuck. And the mental problems would cause physical problems and I would still die early… But maybe not, I can’t possibly know. Fortunately I can choose and even with fails, I can keep my woe okay enough. I like to be an omnivore, be it no or much meat. Not like little meat has a significant chance at this point but I probably could live quite healthily as a vegetarian low-carber if some outer force would demand so. It wouldn’t be ideal, I hope it never happens but I wouldn’t suffer much or get sick… But it’s just a hypothesis again (based on my experiences in my younger times but with less knowledge and on a way worse woe. even my exercise wasn’t good enough).
I don’t need sub 20g but 20g from plants is awfully much for me, that easily messes with my mind. I prefer it being 0-2g, occasionally, with a good reason a bit more… But I still fail a lot (it’s still not so bad, I can handle much more if it’s an isolated happening). In average, I should get the (vast) majority of my carbs from animals, that’s the right way. It’s needed for me staying on keto, actually. It wasn’t always the case but it is now.
And I don’t believe that a plant matter that is designed to be eaten because the plant itself wanted that is toxic, it’s not very logical but I don’t care anyway. I can handle it in moderation. (Fruit. The number one enemy to my carnivore plans nowadays. Even my disdain towards sugar isn’t effective enough.)
Many other plant matter has problematic substances, it’s known. But as my body handles them quite fine, it’s really my choice and I don’t need to worry about it. When I consumed 100 times as much every day, I still felt no problem so this drastically reduces amount should work wonderfully. While worrying definitely would harm my health.