Thanks for the well reasoned comment.

The more I dig, The more I find that can be issues for vegans. It's not just B12. Albumen, DHA, Vitamin K2, and the healthy saturated fats are just some of the missing elements in the vegan diet. Plant derived ALA converts to DHA only about 2% to 5%. It's just not enough, our brains need more. This does not even include the huge overdose of omega-6's that vegans have to try to balance to limit inflammation. High omega-6 content is also a problem with the grain fed meats.

Brant Cortright, Ph.D. in his book 'The Neurogenesis Diet and Lifestyle' discusses a bit of this, though it is not the main focus of the book, and not the only resource discussing this.

Genetics is a substantial part of the puzzle, but epigenetics is a handle that we have to alter how the genes are expressed. Diet and environment play large parts in this.

I find, that in all anti-meat arguments, the difference is never made between the factory farm, feed lot, grain fed meat and the healthy, pastured, grass fed, grass finished meat, devoid of feed treated with pesticides, herbicides, and devoid of animal treatments with antibiotics, hormones, and feed efficiency increasing drugs. It usually seems just a bit disingenuous to me, hiding behind poorly considered pretenses at morality to bolster a vegan argument with so many obvious holes. There is no sound logic supporting the presupposition that veganism of vegetarianism is more or less moral than omnivorous dietary habits.

Torturing animals with the wrong food, and drugs and hormones they've never encountered in nature, does not lead to a positive outcome for the animal regardless of it's end, but that does not render omnivorous diets immoral. It could even be that carnivores are immoral, but I doubt it.