>My digestive system got wrecked trying to be on a mostly vegetarian diet over several years after the housing bubble popped. The gist of it is that the lectins (and other defense mechanisms in the husks) of legumes and nightshades disrupt the mucus lining of the intestines, which leads to leaky gut and stool getting into the body cavity and blood (leaky gut), which may lead to autoimmune diseases like colitis and arthritis.

Umm...did you cook the plants before eating them? Cooking destroys like 99% of lectins.

>Something about animal protein heals this lining, probably because humans evolved as scavengers eating leftover kills and carrion from top predators.

This sounds like total pseudo-science new age woo. No organism EVER directly incorporates foreign protein into itself. Its always broken down completely first, so the structure or origin of these "animal proteins" doesn't matter.