[AstralStorm]

The real stinger for vegan diets, but also poor meat based ones is lack of certain known micronutrients. Mostly D, B12. Potentially also potassium, magnesium, molybdenum. Some investigational ones like boron as well.

This is because he of the food chain is deprived and in case of D and B12 these really are not available in plant sources only.

[GrzegorzWidla]

Animals that haven't eaten natural diet and haven't seen the sun get B12 shots before slaughter. 99% of meat consumed is so poor that majority of population is B12 and vitamin D deficient despite eating it regularly.