[pmoriarty]

Not only that, but B12 isn't actually produced by any of the animals which make up those "animal products" which allegedly have "plenty" of B12 in them. The animals, if they have B12, get it from eating vegetables which have bacteria on them.

These days, however, many animals destined for the dinner table are pumped full of antibiotics (which may kill those B12-producing bacteria), are fed other animals or sterilized grains/vegetables. So it is quite possible that the animals themselves aren't getting adequate B12, and as a result even animal eaters might have a B12 deficiency.

My own doctor recommends all his patients, whether or not they're vegetarian, take B12 supplements.

[cpncrunch]

From wikipedia:

"Ruminants, such as cows and sheep, absorb B12 produced by bacteria in their guts"

[Raphmedia]

Fun fact: Rabbits eat their fecal pellets (they have soft and hard poops, pellets are the hard ones). Those are filled with half digested plant matter. Since they are exposed to bacteria during the first digestion, those fecal pellets are full of vitamins. B12 is one of them. They often eat those dried pellets directly from their fur as breakfast to get the energy to start the day.

[pmoriarty]

And how do the bacteria get there? Do they get there if they're fed sterilized food or other cows? And are the bacteria killed off by the antibiotics they're given?

[dualogy]

> And how do the bacteria get there?

Pre-seeded during breast feeding, as happens across all mammals. How many billions of years do you want to go back on this question?

> And are the bacteria killed off by the antibiotics they're given?

Evidently not, as in developed country sick animals don't get turned into meat foods on principle and by law --- so they don't show up deficient. If they lived for 9 decades like we do, they might (or not). But they don't.

[tgb]

But you can just measure whether animal eaters (tend to) have a B12 deficiency or not - you don't need to know any of this. Is your doctor recommending this based off a long chain of reasoning or based off of a study just directly measuring the rates of B12 deficiency? Since the latter is much easier and is what you actually care about.