The theory is based on a very and i mean very out-dated study from the 1960's by Halstead et al where he reported on the Vitamin B12 levels of a group of villagers in Iran. He concluded from his report that Vitamin B12 deficiency caused by a deficient diet must be very rare.
Firstly before we even get to the nitty gritty of this study, we know from a wealth of current research that his conclusion is now false and that Vitamin B12 deficiency is extremely common in vegans and is caused directly from the lack of dietary B12 intake and not other compounding factors.
One fact we know for sure from the sheer mountain of scientific research on Vitamin B12 and vegan diets is that vegans are commonly deficient in Vitamin B12 and many suffer from hyperhomocysteinemia as a result. Elevated homocysteine levels is also a risk factor for the development cardiovascular disease.
Anyways lets get back to the study, two groups of villagers were studied. The first group it says "subsisted on a diet deficient in animal protein". However in the next sentance the study contradicts itself because it explains that they ate a diet of whole wheat bread almost exclusively with a small amount of a milk product called mast, similar to yogurt once or twice a week, and a little meat or chicken not more than once a month.
To start with the above does not in anyway correlate to a diet "deficient in animal protein", they seem to have completely ignored the fact that whilst these Iranians might have been on a low animal protein diet, they still consumed dairy foods once-twice weekly and meat once a month, both of which are reliable and rich sources of Vitamin B12.
Whilst the intake of animal foods is low by western standards, in theory it is still potentially enough to sustain normal Vitamin B12 levels in otherwise healthy individuals.
Vitamin B12 is a nutrient which is stored in the liver, this is part of the reason why when many go strict vegan they don't develop B12 deficiency/anemia for a few months to even a year in some individuals.
This article on the Vegan Health.org website seems to have brought alot of confusion to many readers, infact many vegans use it as justification for following strict vegan diets, which contain NO animal foods. Id like to point out again that the Iranian villagers in the study were still consuming a small amount of animal foods weekly, for anyone who hasn't read the full study.
To be fair to the study, it does point out the possibility that the reason why these Iranian villagers B12 levels were normal could be because they were still consuming animal foods regularly DUH....., seems fairly common sense to me, especially considering the depth of current scientific research we have on vegan diets, vitamin B12 deficiency and the resulting hyperhomocysteinemia that the majority of these B12 deficient vegans end up suffering from.
However the study also offers two other potential explanations why the Vitamin B12 levels in these individuals were normal. One is that gut bacteria in these individuals was different to others due to their high carbohydrate diet and that they were possibly synthesizing their own B12.
The gut bacteria does produce some Vitamin B12, however there is no research to suggest that its enough to ward off deficiency or enough to waive dietary intake of Vitamin B12. There are plenty of vegans who consume prebiotic fiber rich diets, fermented foods(rich source of beneficial bacteria) and other B12 analog foods such as seaweeds/algaes regularly, yet we consistently see that the majority of these individuals still end up B12 deficient as a result of following strict vegan diets.
The third possibility according to the study is that because the Iranian villagers live with their farm animals, that they might have been unknowingly consuming the feces of these animals, which is thought to contain large amounts of cobalamins including cyanocobalamin(Vitamin B12) according the study.
To me the above two theories are pushing the boundaries of logic in my opinion, the most likely logical explanation for their normal Vitamin B12 levels was the fact that these individuals were consuming Vitamin B12 rich animal foods such as dairy products up to twice weekly, whilst boosting their intake further with meat/chicken once a month.
To use this very out-dated study as justification of following a strict vegan diet containing NO animal foods would be a potentially dangerous decision in my opinion and one that would likely yield low Vitamin B12 levels as we see from the latest research on Vitamin B12 status and vegan diets.
1. Serum Vitamin B12 Concentration in Dietary Deficiency