https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5522483/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5522483/ Shows Vegan and Ovo-Lacto Vegetarian neck and neck.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5522483/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5522483/ Shows Vegan and Ovo-Lacto Vegetarian neck and neck. As another poster pointed out, in many areas living a pure vegan diet is far WORSE for the environment as you have to expend considerable CO2 getting the correct foodstuffs there. There's also the open question about many countries where the land is only suitable for pasture as it's not arable.