Who would fund such a study? There’s no money in it.

Food politics is awful and leads people to make terrible decisions. People develop health problems due to pursuing plant only diets (stuff like vitamin B deficiency, anemia, etc).

Many overall health issues can be helped by teaching people to eat smaller, balanced meals and less focus on extreme diets.

1-year vegan here, no new health issues to report. I supplement vitamins D and B12 and omega-3 fats.

There are people for whom a vegan diet works. You seem to be one of them. I tried it a few times, and no matter what I supplemented, I would lose weight rapidly. I understand that it can turn into a moral argument as well, except that I kill fewer animals than you to eat. Responsibly-grown meat is less detrimental to local ecosystems than vegetables.

It isn’t survivor bias when the giant red rashes all over your body go away after nothing else has worked your entire life and your doctor says that for that to happen is impossible. It’s overlooked science.

But there could still be survivor bias in there to some degree. We need proper interventional studies.

My wife has psoriasis, she has recently (ish) switched to a plant based diet, her psoriasis has cleared up too. She isn't making claims that her change in diet fixed it.

Maybe it's a change in the diet that helped? Not a change to a specific, but rather a change in general.

Very possible, but diet changes usually go hand in hand with other lifestyle changes too. It could be any one of them or a combination, and it can also be person specific.

If she is plant based now, she could have only been SAD before? This is the reason why vegans and vegetarians think their diets are good, because literally anything besides the SAD is an improvement. She is a reduction in symptoms because of a reduction of sugar and other things. Put her on carnivore for a month and if she doesn’t experience anything I’ve described then I’ll eat my hat.

SAD? She has always had a good diet with low sugar intake, her change was literally to cut out meat from her existing diet.