[Dr. Sivana]

but Vitamin B12 doesn’t have many sources but beef.

Well, there's clams and sardines. Other forms of meat (lamb, even chicken) have plenty. Some in eggs as well.

But yes. I just looked up non-animal sources of Vitamin B12. All of them "fortified". Then I asked, how are they fortified? Collecting lots of the right bacteria and putting it in products like yeast.

OK, that process is not something the pilgrims, or ancient Tibetan Monks, Bushmen, Aztecs, or Egyptian Pharoahs could have indulged in. Now I can extend my argument: how can we be meant to have a vegan diet when it wasn't possible to get all needed nutrients with one until the 20th century?

[TigersEye]

Tibetan monks would have no problem eating meat. In fact they'd pretty much have to living in Tibet. But it would be counter to the views of Vajrayana Buddhism to make distinctions like that no matter where they lived.

Exploring the Diversity of Livestock in Tibet: Beyond Yaks

[metmom]

We weren’t.