I used to fast everyday, when I break it sometimes I eat a lot of meat, other days I don't want any and eat more nuts and veggies instead. I once went a whole week just eating a shitton of nuts and vegetables when I break my fast, and damn, my shits were amazing, but pretty much the same as when I eat meat. Kind of off-topic, I guess, but if you really want some health benefits without restricting the type of food you want to eat, I recommend intermittent fasting. It basically allows your body time to rest and repair when you're not digesting, and I've noticed numerous improvements in my health, even when I don't fast.
About the health studies, I honestly think health research is fickle. For example, low-carb diets are great in the short-term, but on the long-term they even out with normally calorie-restrictive diets, mainly because the body doesn't lose fat exponentially.
Long-term studies are difficult to conduct in themselves, but long-term nutritional studies are even worse in that regard, hence a lack of consensus. For the benefits of vegan diets, I think it's a result of being more health conscious and intaking more nutritious veggies rather than removing animal products. I could be completely wrong. The only solution, if you want to achieve anything, is to have some common sense (limit junk, don't drink calories) and then experiment with yourself (reasonably) and see what your body can tolerate. Have fun with it.
About the health studies, I honestly think health research is fickle. For example, low-carb diets are great in the short-term, but on the long-term they even out with normally calorie-restrictive diets, mainly because the body doesn't lose fat exponentially.