"McDougall does have a point when he says that there is no good evidence so-called low B12 causes any diseases in vegans. This is the core of the debate. Most diseases that are associated with low B12 are found in the elderly who are in fact eating meat and dairy."
And:
"At the end of the day it has been shown that you can eat certain plant foods (chlorella in particular and purple nori) and they do increase plasma B12 (as measured by methy malonic acid) more so that meat and eggs do."
My quick response:
I followed McDougall and veganism for about 10 years. I made me sick. I saw many people get benefits in the first 1-2 years, then get ill. I saw babies impaired by B-12 deficiency in mothers. The idea that we have no evidence of B-12 deficiency causing illness in vegans and that B-12 deficiency diseases mostly occur in elderly omnivores is a crock of corn grits.
Vitamin B12 deficiency is associated with coronary artery disease in an Indian population.
Nutritional vitamin B12 deficiency in a breast-fed infant of a vegan-diet mother.
Severe vitamin B12 deficiency in infants breastfed by vegans
Metabolic complications and neurologic manifestations of vitamin B12 deficiency in children of vegetarian mothers
Subacute Combined Degeneration of the Spinal Cord in Vegetarians: Vegetarian's Myelopathy [free full text, includes radiographs of the lesions]
Pancytopenia in nutritional megaloblastic anaemia. A study from north-west India.
Low red and white blood cell counts in long term veg*ns and increased infections.
Vegetarian diet and cobalamin deficiency: their association with tuberculosis. [Full text, found nearly 3 times greater incidence of tuberculosis among vegetarians compared to omnivores.]
Vitamin B12 deficiency due to a strictly vegetarian diet in adolescence.
Brain damage in infancy and dietary vitamin B12 deficiency
A syndrome of methylmalonic aciduria, homocystinuria, megaloblastic anemia and neurologic abnormalities in a vitamin B12-deficient breast-fed infant of a strict vegetarian.
Low bone mineral density and bone mineral content are associated with low cobalamin status in adolescents.
Signs of impaired cognitive function in adolescents with marginal cobalamin status. [full text]
The commenter also claimed:
"At the end of the day it has been shown that you can eat certain plant foods (chlorella in particular and purple nori) and they do increase plasma B12 (as measured by methy malonic acid) more so that [sic] meat and eggs do."
Even veganhealth.org reviews the evidence and concludes we do not have evidence that chlorella and nori prevent B-12 deficiency (because they contain analogues).
On the page B12 in Tempeh, Seaweeds, Organic Produce, and Other Plant Foods you will find this:
"Until chlorella is tested on humans to determined whether it lowers MMA levels, it should not be considered to be a reliable source of vitamin B12, especially since the study by Pratt & Johnson showed no vitamin B12. "
This commenter also wrote:
"And this study found that meat and eggs do nothing to increase plasma B12 - "Dietary sources of vitamin B-12 and their association with plasma vitamin B-12 concentrations in the general population: the Hordaland Homocysteine Study.""
The abstract states: "Plasma vitamin B-12 was associated with intakes of increasing amounts of vitamin B-12 from dairy products or fish (P for trend <0.001 for both) but not with intakes of vitamin B-12 from meat or eggs. For the same content of vitamin B-12, intake from dairy products led to the greatest increase in plasma vitamin B-12. Total intake of vitamin B-12, particularly from milk and fish, decreased the risk of vitamin B-12 concentrations <200 pmol/L and impaired vitamin B-12 function (vitamin B-12 <200 pmol/L and methylmalonic acid >0.27 micromol/L) in the total group and in 71-74-y-old subjects."
So this commenter ignores the finding that fish and milk do raise B-12, selectively citing the finding that B-12 from meat or eggs did not raise levels. I haven't read the full text, but I doubt they actually assayed the meat and eggs consumed, rather they probably relied on tables of nutritional value to estimate intakes of B-12 from meat and eggs.
This could mean the meat and eggs these people ate (factory farmed) had little B-12, compared to fish (mostly wild) and milk, and it does not prove anything about meat and eggs from grass fed animals. Further, fish and milk did increase B-12, so animal products did effectively raise B-12. This certainly does not support veganism.
Humans are omnivores and you pursue veganism at your own risk.
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