One interesting remark in one of Joe Rogan's interviews with a former vegetarian, was somewhat like the following ...

He stated most animals can be eaten by humans, but most plants cannot. Because plants cannot move, plants need to have some innate defences to prevent being killed before being able to reproduce and as such many plants are poisonous. Humans apparently have evolved to be able to disregards some poisons in some plants.

Also, in this interview the former vegetarian stated that if humans were to eat pretty much all of the meat of the animal (including liver, heart) they would get most of the vitamins required to stay in good health.

Now I don't know exactly which person Joe interviewed. Might have been Paul Saladino.