Vitamin B12 is produced only by bacteria. Not yeast.
It’s incredibly difficult to get sufficient quantities of B12 outside of meat products or manufactured supplements.
It’s incredibly difficult to get sufficient quantities of B12 outside of meat products or manufactured supplements.
So either way your B12 is coming from supplements. It's either in a pill already, or the flesh of animal who didn't want to die, and they simply took the pill on your behalf.
Most nutritional yeast is supplemented with B12. It's a good source of protein and other minerals.
Many vegetarians also eat fermented pickles that contain B12 naturally, though you do have to eat rather a lot to get sufficient B12.
By contrast, most non-vegetarians are very deficient in fiber, and nobody ever seems to bother about it.