There's really no way to answer those outcomes broadly because, for the vast majority of human beings, we don't count our calories or compute the macronutrients in our food. It's very difficult to see this unless you perform the study on twins, since birth, maintaining distinctly separate, perfectly controlled diets. The most consistent take is looking at it from an anthropological perspective - plenty of societies throughout history fed on a vegetarian lifestyle, which continues to persist today.
It would be interesting to see the stats of a country like India though, where you don't have confounders like vegetarianism often being a class signal like in the developed world. Although the more I look into it, the more I find that "vegetarian" is a pretty loose label there.
What societies in the past have mainly been vegetarian? None except India seem to persist to this day. I hear the human race took a pretty big hit in the early agricultural era as far as life expectancy goes.
