> [bad reaction] I think it's risky to supplement methyl donors in substantial quantity, such as choline, betaine, methionine, and S-adenosylmethionine. > The amount of methyl in that form of B12 is so tiny that I think it's more likely an allergic reaction; folic acid is allergenic too, and the slightly different manufacturing processes could account for different reactions to different products. > Intestinal bacteria are an important source of B12, and many plant materials contain some. Carotene can be converted to vitamin A when B12 is available. I don't think the real causes of a B12 deficiency are known. A generous dietary source of both A and B12 is desirable, but usually not essential. I think the main reason for having a significant amount of fat in the diet is for its effect on digestion. [Source](https://lowtoxinforum.com/threads/ray-peat-email-advice-depository.1035/post-230414)