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(Comparative Anatomy and Physiology Brought Up to Date--continued, Part 7C)

Key Nutrients vis-a-vis Omnivorous
Adaptation and Vegetarianism (cont.)

Vitamin B-12: Rhetoric and Reality (CONT., 3 OF 5)

B-12 in spirulina and other plant foods

Microbial assays for B-12 are unreliable. A common misconception in vegan circles is that fermented foods and spirulina contain B-12. This claim may, at times, be supported by lab tests for B-12 based on the USP (U.S. Pharmacopeia) assay methods.

Unfortunately, as explained in Herbert et al. [1984] and Herbert [1988], the USP assay method for B-12 is unreliable. The assay measures total corrinoids--that is, true B-12 plus analogues (forms of B-12 that are not metabolically active in the body)--and the analogues have the potential to block the absorption of true B-12 by occupying B-12 receptor sites. A preferred, reliable test that can differentiate between true B-12 and corrinoids is provided by differential radioassay. The assay problem must be considered in evaluating "old" studies on B-12.

Spirulina and tempeh contain mostly analogues of B-12. Herbert [1988] reports that tests on tempeh, a fermented soy product, and spirulina revealed that they contained almost no true B-12, i.e., the "B-12" they contained (per USP assay test) was predominantly analogues. Herbert [1988, p. 857] reports:

We suspect that people taking spirulina as a source of vitamin B-12 may get vitamin B-12 deficiency quicker because the analogues in the product block human mammalian cell metabolism in culture [i.e., in the lab] and we suspect that they will also do this in the living human.

The presence of analogues, rather than true B-12, in fermented foods makes them unreliable sources for B-12.

Effects of cooking and processing on B-12 in foods

Available information not well-controlled enough to provide definitive answers. Recognizing that some vegans advocate raw-food diets, the question of the effect of cooking and processing on B-12 levels is relevant. The information on this topic (available to this writer) is less clear than desired. That is, for a reliable comparison to be made, tests must be made on both raw and cooked samples from the same base lot of raw foods, and a reliable assay method must be used. Comparison of B-12 levels, raw vs. cooked, via standard nutritional tables, is not an optimal comparison method, as it may not be clear whether the above conditions for comparison are met, and/or if reliable assay methods were used in the table analysis.

The limited evidence available, though, suggests that cooking reduces B-12 levels, though the exact extent is, unfortunately, unclear.

The possibility that plant foods might contain some B-12 will be discussed later herein. At that time we will note that there is little or no data on the effect of cooking on B-12 levels in plant foods.

Is biologically active B-12 produced by intestinal bacteria?

Claims of intestinal B-12 production may be based on insufficient evidence. Albert et al. [1980] is sometimes cited as evidence that B-12 producing bacteria can exist in the small intestine. Sometimes explicit claims are made, e.g., that intestinal bacteria allegedly can produce adequate B-12. Baker [1981] and Nutrition Reviews [1980] are related citations that comment on Albert et al. [1980].

However, a careful reading of Albert et al. [1980] shows that it used bacteriological assays, which are of lower reliability, to measure B-12 levels. Specifically, the most accurate bacteriological assay they used is Ochromonas malhamensis. Note that Ochromonas is the most accurate bacterial assay method for B-12; however, even it may report values for some analogues as part of its "B-12" results [Schneider and Stroinski 1987, Tables 3-2, 5-3 to 5-5, pp. 56-57, 119-123]. Herbert and Das [1994, p. 405] apparently regard all the bacterial assay methods as being less reliable than differential radioassay; also see Herbert et al. [1984] and Herbert [1988] for related information.

Additionally, the data obtained in Albert et al. [1980] comes from isolated bacterial cultures. Therefore, it is unclear whether the bacteria would produce similar amounts of B-12 under the conditions present in the intestines. This point is discussed in Albert et al. [1980], but is sometimes ignored by dietary advocates with an ideological interest in minimizing the requirement for B-12 in the diet. The bottom line in the paper of Albert et al. [1980] is that it shows certain intestinal bacteria might produce B-12, but it is unclear whether/how much might be produced (and absorbed) under actual conditions in the small intestine.

Langley [1995, p. 74] summarizes the situation nicely:

In some people, B-12 producing bacteria certainly exist in the small intestine where the vitamin manufactured can, in theory at least, be absorbed. Exactly what contribution this makes to the daily B-12 intake of vegans remains to be clarified.

Also recall the discussion above (from Herbert [1984]) regarding the achlorhydric stomach being colonized by bacteria that produce abundant analogues of B-12. Analogues (which block uptake of true B-12) are a major concern whenever one discusses the possibility of B-12 being produced in the small intestine.

Direct coprophagy: a reliable (vegan?) B-12 source

Note: this section may be considered to be in poor taste--both figuratively and literally--by some readers. It is included here for completeness, and in the event certain (extremist) fruitarian/veg*ns might be interested in experimenting with a vegan (?) source of vitamin B-12 that is truly radical in character.

B-12 produced in, but cannot be absorbed from, the human colon. The human colon contains bacteria that produce vitamin B-12, and fecal matter is a rich source of B-12. This raises the question of whether B-12 can be absorbed from the colon. From Herbert [1988, p. 852]:

In one of the less appetizing but more brilliant experiments in the field of vitamin B-12 metabolism in the 50s, Sheila Callendar (7) in England delineated that colon bacteria make large amounts of vitamin B-12. Although the bacterial vitamin B-12 is not absorbed through the colon, it is active for humans. Callendar studied vegan volunteers who had vitamin B-12 deficiency characterized by classic megaloblastic anemia. She collected 24-h stools, made water extracts of them, and fed the extract to the patients, thereby curing their vitamin B-12 deficiency. This experiment demonstrated clearly that 1) colon bacteria of vegans make enough vitamin B-12 to cure vitamin B-12 deficiency, 2) the vitamin B-12 is not absorbed through the colon wall, and 3) if given by mouth, it is absorbed primarily in the small bowel.

Herbert et al. [1984] collected the 24-hour fecal output from 6 men. They found that the (24-hour) total fecal output contained ~100 mcg of total corrinoids, of which only ~5 mcg was true B-12 (the remainder being analogues). (Note: see Mozafar [1994] for a table of B-12 levels in manure, feces, soil, sludge, etc.) Given this, the work of Callendar mentioned above could be taken to suggest that the true B-12 in the feces (if reingested and passed back through the small bowel) would be absorbed, despite the substantial amount of analogues present.

Any takers? Further, the daily output of ~5 mcg versus the RDA/RDI of 1-2 mcg suggests that a direct coprophagy level (i.e., reingestion of feces) of 20-40% of output will meet requirements for B-12. Might this qualify as the only truly reliable, vegan (?) source of B-12? Will coprophagy be the next fad among certain fruitarian extremists? (Obligatory warning: coprophagy, and the handling of feces, is unsafe and increases the risk of transmission of parasites and diseases. Coprophagy is not recommended.)


(Recent Research on Vitamin B-12 Absorbed in Plants via Manure)

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GO TO PART 1 - Brief Overview: What is the Relevance of Comparative Anatomical and Physiological "Proofs"?

GO TO PART 2 - Looking at Ape Diets: Myths, Realities, and Rationalizations

GO TO PART 3 - The Fossil-Record Evidence about Human Diet

GO TO PART 4 - Intelligence, Evolution of the Human Brain, and Diet

GO TO PART 5 - Limitations on Comparative Dietary Proofs

GO TO PART 6 - What Comparative Anatomy Does and Doesn't Tell Us about Human Diet

GO TO PART 7 - Insights about Human Nutrition & Digestion from Comparative Physiology

GO TO PART 8 - Further Issues in the Debate over Omnivorous vs. Vegetarian Diets

GO TO PART 9 - Conclusions: The End, or The Beginning of a New Approach to Your Diet?

Back to Research-Based Appraisals of Alternative Diet Lore

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