Here's a strange, but not totally uncommon theory regarding why vegans who don't take supplements do not develop a B12 deficiency.
I wonder where this... anal fixation comes from? How was this myth about human faeces as a usable B12 source created?Human faeces can contain significant B12. A study has shown that a group of Iranian vegans obtained adequate B12 from unwashed vegetables which had been fertilised with human manure. Faecal contamination of vegetables and other plant foods can make a significant contribution to dietary needs, particularly in areas where hygiene standards may be low. This may be responsible for the lack of aneamia due to B12 deficiency in vegan communities in developing countries.
First of all, this Iranian study on vegans apparently doesn't exist. There is a study, but these people weren't vegans....
We know that not only does the B12 in faeces represent a very small part of the stools, but only a small part (circa 5%) of this B12 is active B12. According to Victor Herbert and others, "24-hr human stool contains only about 5 µg of cobalamin but about 100 µg of apparent analogues". First of all; these people tend to suggest that B12 analogues always will block the absorption of active B12. There is no evidence for this, but if they would have been right, NO B12 would have been absorbed from their stools. The poor 5 mcg would have lost the fight against the massive 100 mcg of analogues.
If those who think that the digestive systems of healthy humans are capable of differentiating between true, active B12 and inactive analogues are right, there would be another dilemma, namely that even if we consume 5 mcg B12, we don't absorb 5 mcg B12.
It has been said that if you eat something containing B12 only once a day, it should contain at least 10 mcg B12 in order to provide you with the B12 you need (I could say a lot about this, but won't do this right now! ) .
Back to the "faecal contamination of vegetables and other plant foods" as a "significant" B12 contribution... The numbers above shows that even if we would be able to absorb every all the 5 mcg B12 in humans stools (by eating everything that came out of our bottoms), the portion would have been too small if such a 'meal' was eaten once pr. day. In order to get those 10 mcg this way, one human would need the stools of two persons daily.
I've seen these theories about getting 'faeceal B12' from improper hand washing and unwashed vegetables several times, and it's somewhat fascinating that these people believe in what they write! It doesn't help to mix stools with other dirt (like the pieces of soil on unwashed carrots) either, because the same principles apply to soil: B12 only represents only a tiny part of the soil (circa 1 mcg B12/100g)... and this B12 probably consists of a mixture of active and passive B12. Plus (again): we only absorb some of the B12 we consume.
Proper or improper handwashing: one would probably have to eat just as much stools or soil as one ate food to get sufficient B12 from non-food sources.
Some claim that we would get enough B12 from dirt and bugs present in foods. In another silly thought experiment, I figured out (in an equally non-scientific manner) that one would have to eat an average of 480 billion insects daily to get enough B12. I don't know what's worst, really, 480 billion bugs or 1 kg stools/soil mixture pr. day...
The somewhat sad thing about all this is that some people simply have decided that B12 does not exist in plants, and that if people get B12 from plants, it must be from insect droppings or dirt. I spoke on the phone a few years ago with a guy involved in testing B12 levels in algae, and he seemed disappointed he had found B12 in his studies, and wanted to convince me that the B12 actually didn't come from the algae, but from insects in the lake they took the algae from. I don't know why people are doing these tests if they have decided that they won't trust the results they get...