(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.
- Herbert [1984] reports that dehydration at 200°C (392°F) for 6 days reduced B-12 levels by approximately one-third. Note that 200°C is well above normal boiling/steaming temperatures.
- Herbert [1984] also reports that boiling in alkali destroys 85% of the corrinoid content, per L. liechmanni (USP, bacterial assay) test. This result is difficult to interpret, as typical cooking practices do not involve boiling in alkali, and the USP test, as discussed above, is not a reliable measure of true B-12.
- Banerjee and Chatterjea [1963] report wide variation in B-12 losses in cooking various types of fish, meat, and milk. B-12 losses, when they occurred, ranged from 23.7-96.4%. However, one fish species in their study showed no loss of B-12, and samples from three fish species (and also goat liver) showed increases in B-12 levels from cooking. (The authors suggest the increase may be caused by cooking increasing the B-12 level in the extraction solvent.) The result that B-12 level for some species increased via cooking, of course, raises questions regarding the overall reliability of their experimental methods and results. Also, their study measured B-12 via microbial assay (Euglena gracilis var. bacillaris), which today is regarded as a less-reliable assay method (does not/may not distinguish analogue forms from true B-12). Banerjee and Chatterjea [1963] also tested 20 types of plant foods, and found no B-12 activity in any of the raw plant foods.
- Heyssel et al. [1966] report that liver boiled in water for 5 minutes lost only 8% of its vitamin B-12 content (vs. raw liver), while muscle meat broiled at 171°C (340°F) for 45 minutes lost 27% of vitamin B-12 (vs. raw meat). [Note: The paper mentions 340°F in one place and 340°C in another. Given that 340°C = 644°F (an unusually high cooking temperature), that figure is probably a typo, and the correct figure is most likely 340°F (171°C).] They note that some of the B-12 they record as lost might actually be contained in the drippings (liquids discarded) in cooking. Their paper also used a Euglena gracilis assay for B-12.
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.)
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(Recent Research on Vitamin B-12 Absorbed in Plants via Manure)
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SEE REFERENCE LIST
SEE TABLE OF CONTENTS FOR:
PART 1 PART 2 PART 3 PART 4 PART 5 PART 6 PART 7 PART 8 PART 9
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
