Cordain on Grains and Vitamin B

Loren Cordain writes (among others) on B-vitamins in his masterpiece Cereal Grains: Humanity’s Double-Edged Sword:

B Vitamins
Diets based primarily or wholly upon plant food sources tend to be either low or deficient in vitamin B12, since this nutrient is found exclusively in animal products [40]. …

Many nutritionists consider cereal grains to be good sources of most of the B vitamins except for vitamin B12. Inspection of table 4 generally is supportive of this concept, at least in terms of the % RDA which cereal grains contain. However, of more importance is the biological availability of the B vitamins contained within cereal grains and their B vitamin content after milling, processing and cooking. It is somewhat ironic that two of the major B vitamin deficiency diseases which have plagued agricultural man (pellagra and beriberi) are almost exclusively associated with excessive consumption of cereal grains. …

Although table 4 suggests that most cereal grains except for oats are relatively good sources of vitamin B6, the bioavailability of B6 from cereal grains tends to be low, whereas bioavailability of B6 from animal products is generally quite high, approaching 100% [60]. Vitamin B6 exists in foods as three nonphosphorylated forms (pyridoxine, pyridoxal and pyridoxamine) and two phosphorylated forms of pyridoxal and pyridoxamine. An additional glycosylated adduct of pyridoxine, pyridoxine glucoside, occurs widely in cereal grains and has been shown to reduce the bioavailability of both nonphosphorylated and phosphorylated forms of vitamin B6 by 75–80% [60, 61]. The presence of pyridoxine glucoside in cereal grains has an overall effect of depressing the vitamin B6 nutritional status [62]. …

Perhaps the least studied of the B complex vitamins is biotin. Animal studies have shown that most cereal grains except maize have very low levels of bioavailable biotin [65, 66], whereas foods derived from animal sources have a high biotin digestibility [66]. Both wheat and sorghum not only have a low biotin bioavailability, but seem to have elements within them which seem to elicit a depression of biotin metabolism [66]. The enzyme, biotinidase, recycles the biotin derived from the turnover of the biotin-dependent carboxylases and from exogenous protein-bound dietary biotin (fig. 1). Whether or not antinutrients present in cereal grains interfere with biotinidase is not known. …

This is now more than a decade old – one would think that our knowledge has improved in the meantime.