We do not recommend a strictly plant based diet, and this is one of the reasons. In the article published by the Weston A. Price Foundation, Myths of Vegetarianism, we learn that it is a myth that vitamin B12 can be obtained from plant sources. The article cites the sources to each of these statements.
Of all the vegetarian myths, this is perhaps the most dangerous. While lacto and lacto-ovo vegetarians have sources of vitamin B12 in their diets (from dairy products and eggs), vegans (total vegetarians) do not. Vegans who do not supplement their diet with vitamin B12 will eventually get anemia (a fatal condition) as well as severe nervous and digestive system damage; most, if not all, vegans have impaired c metabolism and every study of vegan groups has demonstrated low vitamin concentrations in the majority of individuals. Several studies have been done documenting B12 deficiencies in vegan children, often with dire consequences. Additionally, claims are made in vegan and vegetarian literature that B12 is present in certain algae, tempeh (a fermented soy product) and Brewer’s yeast. All of them are false as vitamin B12 is only found in animal foods. Brewer’s and nutritional yeasts do not contain B12 naturally; they are always fortified from an outside source.
There is not real B12 in plant sources but B12 analogues–they are similar to true B12, but not exactly the same and because of this they are not bioavailable. It should be noted here that these B12 analogues can impair absorption of true vitamin B12 in the body due to competitive absorption, placing vegans and vegetarians who consume lots of soy, algae, and yeast at a greater risk for a deficiency.
Some vegetarian authorities claim that B12 is produced by certain fermenting bacteria in the lower intestines. This may be true, but it is in a form unusable by the body. B12 requires intrinsic factor from the stomach for proper absorption in the ileum. Since the bacterial product does not have intrinsic factor bound to it, it cannot be absorbed.
It is true that Hindu vegans living in certain parts of India do not suffer from vitamin B12 deficiency. This has led some to conclude that plant foods do provide this vitamin. This conclusion, however, is erroneous as many small insects, their feces, eggs, larvae and/or residue, are left on the plant foods these people consume, due to non-use of pesticides and inefficient cleaning methods. This is how these people obtain their vitamin B12. This contention is borne out by the fact that when vegan Indian Hindus later migrated to England, they came down with megaloblastic anaemia within a few years. In England, the food supply is cleaner, and insect residues are completely removed from plant foods.
The only reliable and absorbable sources of vitamin B12 are animal products, especially organ meats and eggs. Though present in lesser amounts than meat and eggs, dairy products do contain B12. Vegans, therefore, should consider adding dairy products into their diets. If dairy cannot be tolerated, eggs, preferably from free-run hens, are a virtual necessity.
That vitamin B12 can only be obtained from animal foods is one of the strongest arguments against veganism being a “natural” way of human eating. Today, vegans can avoid anemia by taking supplemental vitamins or fortified foods. If those same people had lived just a few decades ago, when these products were unavailable, they would have died.
Read more in the Vegetarian Tour section of the Weston A. Price Foundation’s website.