B12. It's not in plants. We can add it to plants, but that's an entire industry of itself. Don't know the enviro impact of that, but don't like the idea of relying on big pharma to produce such a requirement. Eating meat really isn't the issue either. It's the kind of meat & how damn much we eat. 3 oz gives all the B12. We eat that x3. But cutting back is insufficient without a move away from inefficient meats like beef. Or we can trust big pharma. I'm going to keep eating chicken.
@NihilVidere
I've been vegan for 30+ years and getting enough B12 has never been an issue for me. We don't need it in large amounts and any impacts of supplementing with B12 can not possibly compare with the environmental and other costs of livestock farming. I hear you, but every animal slaughtered is one too many for me.