In his November 2007 Newsletter, Dr. John McDougall, a tireless advocate of a strict vegetarian (vegan) diet, writes the following:
“Since the usual dietary source of vitamin B12 for omnivores is the flesh of other animals, the obvious conclusion is that those who choose to avoid eating meat are destined to become B12 deficient. There is a grain of truth in this concern, but in reality an otherwise healthy strict vegetarian’s risk of developing a disease from B12 deficiency by following a sensible diet is extremely rare—less than one chance in a million.”
Dr. McDougall apparently has not read the scientific literature on B-12 deficiency in vegans and vegetarians. In 1999, Haddad et al reported a study that included 25 vegan participants. Of these, “2 had macrocytosis (mean red cell volume 398 fL), 3 had circulating concentrations of vitamin B-12<150>376 nmol/L, which is the critical cutoff point that represents
3 SDs above the population mean.” Macrocytosis represents gross vitamin B-12 deficiency, which in this study occurred in 2 of 25 vegan individuals, or 8% -- an 80,000 times greater incidence than “one-in-a-million” (i.e. 0.0001%). Three of 25 or 12% had low VT-B12 concentrations, and 5 of 25 or 20% had elevated methylmalonic acid concentrations, which most experts consider the most sensitive indicator of vitamin B-12 deficiency.
Furthermore, the Haddad et al reported that “Although the average time subjects consumed a vegan diet was 4.2 y in this study, the data showed that 10 of the 25 vegans had at least one indicator of vitamin B-12 deficiency, either macrocytosis, low serum vitamin B-12, or elevated methylmalonic acid concentration (Table 4).” Therefore, this study alone suggested that approximately 40% of vegans may suffer from some degree of vitamin B-12 deficiency. In other words, this study recorded an incidence of B-12 deficiency 400,000 times as high as McDougall claims. Meanwhile, not one of the non-vegetarians had any of the indicators of B-12 deficiency.
Of interest, in table 2 of this paper, Haddad et al report that average intakes of B-12 from both food and supplements did not differ much between the vegans and nonvegetarians. This suggests strongly that B-12 supplements and fortified foods (the only significant sources of B-12 in vegan diets) do not prevent B-12 deficiency in long-term vegans. This could occur because the form used in supplements and fortified foods, cyanocobalamin, differs from the form supplied by animal foods.
This deficiency also affects lacto-vegetarians. In 1999 Hokin and Butler reported a study of 340 Seventh Day Adventist Vegetarians, 245 of which were lactovegetarians or vegans. In the vegetarians, 53% had serum B-12 levels below the laboratory reference range of 171 pmol/L, and 73% had levels below 221 pmol/L, the level identified as normal for an individual with adequate production of the intrinsic factor required for vitamin B-12 absorption. By conducting the Schillings test for intrinsic factor activity, Holin and Butler determined that dietary inadequacy caused the B-12 deficiency in 70% of the vegetarian subjects in this study.
In 2003, Herrmann et al conducted a study of 66 lactovegetarians or lactoovovegetarians
(LV-LOV group), 29 vegans, and 79 omnivores. This team tested three indicators of B-12 deficiency in all subjects: holotranscobalamin II, methylmalonic acid (MMA), and homocysteine levels. Low serum B-12 or holotranscobalamin II, or elevated MMA or homocysteine, indicate B-12 deficiency. They reported:
“Irrespective of vitamin usage, low vitamin B-12 concentrations (<> 271 nmol/L) was found in 5% of the omnivores, 61% of the LV-LOV subjects, and 86% of the vegans.”
Again, the facts dispute McDougall’s claim. In this study, signs of B-12 deficiency appeared not only in up to 90% of vegans, but also in up to 73% of LV-LOVs, and this despite use of vitamin B-12 supplements among the vegetarians.
In table 2 of this study they report the following findings among subjects not using vitamins:
• Normal B-12 status occurred in 78% of omnivores, 11% of LV-LOVs, and only 8% of vegans.
• Stage I or II B-12 deficiency occurred in 10% of omnivores, 21% of LV-LOVs, and 8% of vegans.
• Stage III B-12 deficiency occurred in 3% of omnivores, 60% of LV-LOVs, and a disconcerting 83% of vegans.
McDougall also claims that vegan diets work the best for reduction of homocysteine because of their high levels of folate and low levels of methionine—an amino acid abundant in meat but not plant proteins. But in this study, vegans and LV-LOVs, not omnivores, had the highest homocsteine (tHcy) levels, due to their B-12 deficiency. Herrmann et al wrote:
“We found tHcy concentrations <> 7 nmol/L). In contrast, hyperhomocysteinemia occurred in the LV-LOV subjects and vegans when serum folate was as high as 42.0 nmol/L.”
In other words, high folate and low methionine intakes do not protect against elevated homocysteine. High homocysteine appears linked to heart disease, cancer, osteoporosis, and many other common degenerative conditions, none of which occurred in healthy hunting and gathering groups.
So McDougall doesn’t have his facts correct about the incidence of B-12 deficiency or elevated homocysteine levels in vegetarians. But he goes on from that error to add:
“Take a moment to compare the possible consequences of your dietary decisions. You could choose to eat lots of B12-rich animal foods and avoid the one-in-a-million chance of developing a reversible anemia and/or even less common, damage to your nervous system. However, this decision puts you at a one-in-two chance of dying prematurely from a heart attack or stroke; a one-in-seven chance of breast cancer or a one-in-six chance of prostate cancer. The same thinking results in obesity, diabetes, osteoporosis, constipation, indigestion, and arthritis. All these conditions caused by a B12-sufficient diet are found in the people you live and work with daily. How many vegans have you met with B12 deficiency anemia or nervous system damage? I bet not one! Furthermore, you have never even heard of such a problem unless you have read the attention-seeking headlines of newspapers or medical journals.”
This paragraph contains several fallacies. First of all, he asserts a false dilemma: Either eat no animal foods and court a miniscule risk of B-12 deficiency, or eat “lots of B12-rich animal foods” and incur a high risk of heart attack, stroke, breast cancer, prostate cancer, obesity, diabetes, osteoporosis, constipation, indigestion, and arthritis.” This dilemma is false in several ways:
• He suggests falsely that you have only two choices, either eat no animal foods, or eat an undefined “lots” of them, when in fact a diet can vary from 0% to 100% animal food.
• He has not defined what percent will constitute “lots” of animal food, and though it refers generally to large amounts, by contrasting it with “no” animal food, Dr. he implies without evidence that eating any amount of any kind of animal food will put you at high risk for the listed diseases
• He implies that eating “lots” of animal foods will put anyone or everyone at risk for the listed diseases, and conversely that eating a vegan diet will prevent all these diseases in anyone or everyone.
Traditional Eskimos eat a diet composed of up to 90% animal food, and on their traditional diet, they had a low risk of heart attack and no cancer, no obesity, no diabetes, and no constipation. I do not think the Eskimo diet is ideal, but traditional Eskimo dietary experience certainly disproves McDougall’s implied claim that eating “lots” of animal food causes all the disorders he listed.
Dr. McDougall goes on to cite one study finding that “The human gut also contains B12-synthesizing bacteria, living from the mouth to the anus.” Although apparently true, he fails to mention that in order to produce true vitamin B-12 (cobalamin), these bacteria would need a source of cobalt, since a functional B-12 molecule contains this mineral.
Foods can supply cobalt, either as B-12 or in elemental form. A study by Hokin et al found that in Australia meat and potatoes are the main dietary cobalt sources. Comparing cobalt intakes of 10 omnivores, 10 lacto-ovo-vegetarians, and 10 vegans, Hokin et al found that lacto-ovo-vegetarians had the lowest cobalt intakes, that vegans who ate large amounts of potatoes had cobalt intakes similar to omnivores, and that vegans who did not eat large amounts of potatoes had cobalt intakes similar to lacto-ovo-vegetarians. Hokin et al found no correlation between dietary cobalt intake and serum B-12 concentrations in any of the dietary groups.
Hokin et al reported both vegans and vegetarians had mean serum B-12 levels of 175 pmol/L, compared to 366 pmol/L in omnivores. (As noted above, levels below 221 pmol/L are considered deficient and are associated with macrocytosis and elevated homocysteine in vegetarians.) Hokin et al noted that even the lowest cobalt consumption in the groups studied (6.67 mcg/d) would support the production of 165 mcg of B-12, about 80 times the RDA for B-12 – but that did not happen in the vegans, indicating that human gut flora does not produce significant or adequate amounts of B-12 from dietary cobalt.
Dr. McDougall goes on to discuss the fact that the intestinal flora of ruminant animals (such as cattle, sheep, deer, bison, giraffes, and goats) produce vitamin B-12. These animals ingest cobalt, carbon, hydrogen, phosphorus, and nitrogen by eating grass, a food inedible to humans, and their intestinal flora use that material to produce B-12. They absorb and use some of that B-12, so that the B-12 appears in the meat and milk of these animals, but they also pass much out in their feces.
McDougall goes on to say:
“The [human] colon contains the greatest number of bacteria (4 trillion/cc of feces), and here most of our intestinal B12 is produced. However, because B12 is absorbed in the ileum, which lies upstream of the colon, this plentiful source of B12 is not immediately available for absorption—unless people eat feces (don’t gasp). Feces of cows, chickens, sheep and people contain large amounts of active B12. Until recently most people lived in close contact with their farm animals, and all people consumed B12 left as residues by bacteria living on their un-sanitized vegetable foods.”
Why shouldn’t we gasp? Is he suggesting that it is healthier to eat feces than to eat meat or milk? I venture to say without any scientific reference that people all over the planet feel revulsion at the idea of eating feces, and that no successful culture has failed to recognize the need to take steps to remove fecal matter from foods before consumption.
Moreover, every culture that keeps farm animals does so to have access to meat, milk, and eggs, not so as to have vegetables contaminated with fecal matter. But McDougall writes as if he wants us to believe that in the old days people avoided eating animal products and only kept farm animals so they could have access to vegetables contaminated with fecal matter.
I don’t know of any human group that has a tradition of keeping farm animals just for the purpose of eating unwashed vegetables contaminated with feces. I find his insinuation insulting to the intelligence of the reader and the human race in general. In case the reader or McDougall does not know, consumption of fecal matter can kill by ingestion of deadly coliform bacteria or protozoans. Yet McDougall appears to think it is better to eat vegetables contaminated with fecal matter than to eat animal flesh.
McDougall goes further to say: “Why would a plant-food-based diet, heralded as a preventative and cure for our most common chronic diseases be deficient in any way? Such a diet appears to be the proper, intended, diet for humans, except for this one blemish.”
Okay, one thing at a time. First, here he clearly uses the phrase “plant-food-based diet” to refer only to a vegan diet. But in fact the phrase “plant-based” does not mean plant-only. Any diet that provides more than 50% of its bulk or energy from plant foods can legitimately be called plant-based. What else would you call a diet that provided 75% of its energy from plant foods and 25% from animal foods? I certainly would not call that diet “animal-based.”
A vegan diet is not only plant-based, it is plant-only. Vegans quite commonly apply the concept of dietary base inconsistently. They commonly call the omnivorous diet “animal-based” when in fact the majority of modern omnivores eat plant-based diets, i.e. the bulk of the diet of omnivores comes from plants, not animals. If a diet contains any animal foods at all, vegans call it “animal-based,” but will call a diet “plant-based” only if it is 100% plant food.
Moreover, B-12 deficiency is not the only “blemish” on plant-only diets. Plant-only diets may fail to meet human needs for taurine, DHA, zinc, iron, vitamin B-6, and vitamin A.
Further, what does he mean when he says a plant-only diet is the “proper, intended” diet for humans? Who does he think “intended” for humans to eat a plant-only diet? Does he opine that some supernatural creator “intended” for humans to eat vegan diets? I find this sudden reference to an “intended” diet creepy.
I know many readers may believe in a god, but no one has ever produced any scientific evidence that any of Nature or human physiology occurred as a result of the “intention” of any supernatural entity. In addition, various human tribes have claimed to “know” the existence, will, or intent of many different gods– the Judeo-Christian God, the Islamic Allah, Vishnu, Brahman, Zeus, Poseidon, Buddha, etc. The opinions as to what these entities supposedly “intended” for humans appear quite contradictory. Compare the dietary proscriptions of Islam and Hinduism, or of Seventh Day Adventists and Jews, etc., and you will quickly see that the experts on the gods’ wills for human diets have major disagreements. Even within cults there appears dispute about what the god wants. Some Buddhists claim Buddha prohibits meat-eating, some say not. Some Christians say their God allows meat-eating, some say not.
Discussions of human nutritional requirements require evidence from scientific research, not vague references to the “intended” diet of man without reference to any entity that could have intent (such as humans). Certainly rice did not “intend” for humans to eat its seeds; apple trees did not produce apples for humans; soybean plants do not intend for humans to eat their seeds; and so on.
Nature did not “intend” for humans to eat any diet; rather, humans adapted to eating what Nature provided in the ecological niche humans chose to inhabit. All the scientific evidence indicates not only that humans have always eaten omnivorously, but in fact that prehistoric humans depended primarily on animal-source foods for millions of years during the ice ages.
In fact, humans could not have spread from Africa to inhabit Europe, starting 50, 000 years ago, unless they heavily utilized meat, poultry, fish, and eggs as staple foods. From that time until about 10, 000 years ago, an ice age gripped the planet, and humans moved out of Africa into Central Asia, and from there eventually to Australia, Europe, China, Siberia, and North America. The climate did not allow the earth to produce sufficient quantities of edible plant foods along many of the routes of migration humans followed. So they lived on meat and fish of whatever type they could find.
What every vegan needs to know about B-12: http://www.veganhealth.org/articles/everyvegan/
Another study showing low B-12 levels and elevated homocysteine in vegans and vegetarians:
http://content.karger.com/ProdukteDB/produkte.asp?Aktion=ShowAbstract&ArtikelNr=12827&Ausgabe=224621&ProduktNr=223977
Notes
Haddad et al, Dietary intake and biochemical, hematologic, and immune status
of vegans compared with nonvegetarians, Am J Clin Nutr 1999;70(suppl):586S–93S.
Hokin and Butler, Cyanocobalamin (vitamin B-12) status in Seventh-day Adventist
ministers in Australia, Am J Clin Nutr 1999;70(suppl):576S–8S.
Herrmann et al, Vitamin B-12 status, particularly holotranscobalamin II and
methylmalonic acid concentrations, and hyperhomocysteinemia
in vegetarians, Am J Clin Nutr 2003;78:131–6.
Albert MJ, Mathan VI, Baker SJ. Vitamin B12 synthesis by human small intestinal bacteria. Nature. 1980 Feb 21;283(5749):781-2.
Hokin et al, Comparison of the dietary cobalt intake in three different Australian diets, Asia Pac J Clin Nutr 2004;13 (3):289-291.
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