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

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

Vitamin B-12: Rhetoric and Reality (CONT., 4 OF 5)

Indirect coprophagy: plant foods fertilized with feces/manure

The consumption of plant foods grown in soil fertilized with human manure (occasionally called "night soil") might also provide adequate B-12. Herbert [1988, pp. 852, 854] notes:

The more frequent source of vitamin B-12 in association with plant food is external contamination with bacteria, often of fecal origin...

The fact that stool vitamin B-12 can be important in human vitamin B-12 economy was delineated by James Halsted (11) working with Iranian vegans who did not get vitamin B-12 deficiency... Halsted went to Iran and found that they grew their vegetables in night soil (human manure). The vegetables were eaten without being carefully washed and the amount of retained vitamin B-12 from the manure-rich soil was adequate to prevent vitamin B-12 deficiency.

Note that the first part of the quote above--that B-12 on plant foods is primarily present as contamination--may be outdated, per the more recent research of Mozafar [1994]. The paper of Mozafar is sometimes cited by raw/vegan advocates as "proof" that a raw/vegan diet, if grown in the "right" soil (manured), can provide adequate B-12. Therefore, let's now take a closer look at this research.

Mozafar [1994] grew soybeans, barley, and spinach on three kinds of soils--unenriched soil (control), soil fertilized with raw, dried cow dung, and soil enriched with vitamin B-12. The discussion of Mozafar [1994] in this paper will omit the results from soil enriched with B-12, as it is not an economically feasible agricultural practice at present.

Vitamin B-12 levels were measured using "radioisotope dilution" [Mozafar 1994, p. 307], also called protein-binding. This assay claims a high resolution in distinguishing between true B-12 and analogues.

Plants may absorb B-12 from the soil. Mozafar [1994, pp. 307, 309-310] claims:

[M]ost, if not all, of the B-12 in the plant may be in the free form...

Considering the reports that plant roots and leaves can absorb the relatively large molecules of B-12 from nutrient solutions and transport them to other plant parts (Mozafar and Oertli 1992a) and the belief that plants cannot synthesize this vitamin (Friedrich, 1987; Lehninger, 1977; Smith, 1960), it seems that the observed increase in the concentration of B-12 in barley seeds and spinach leaves fertilized with cow dung is mostly (if not fully) due to the uptake of this vitamin by the roots from the soil and not due to superficial contamination or an increased synthesis within the plant.

The claim that the B-12 in the above experiment was mostly true B-12--and absorbed and taken up by the plants--is surprising in light of the known presence of B-12 analogues in many foods (see the papers by Herbert for discussions on this point). It also raises an important issue: if the assay techniques used by Mozafar did not also measure vitamin B-12/cobalamin analogues, then we really don't know if analogues are present, which could (potentially) interfere with absorption of vitamin B-12 from plant foods.

A later paper by Mozafar--i.e., Mozafar [1997, p. 51]--reports that very little is known about the absorption of B-12 analogues by plants. Note also that the second part of the above quote contradicts the claim by Herbert that B-12 is usually found primarily externally in plants. (The claim by Herbert may be outdated/incorrect; see Mozafar and Oertli [1992] for discussion of their research that shows soybean roots are able to absorb B-12, and the vitamin can be transported within the plant.)

B-12 found in tested plant foods. Mozafar found that the levels of B-12 in barley and spinach grown in untreated (control) soil versus soil treated with cow dung were significantly different. However, the B-12 levels of soybeans were not significantly different for the two soil types.

The B-12 measurements in Mozafar [1994] are frankly hard to interpret as-is. That is, the measurement unit utilized, i.e., nanograms of B-12 per gram of plant food, dry weight, is not meaningful to most readers. To help readers understand the Mozafar results, a part of the results are used below to estimate the amount of each plant food (by itself) needed to get 2 mcg of B-12 per day. The last 2 columns in the table below are the most important--they show the estimated weight (in kilograms and in pounds) of raw plant foods required to satisfy daily B-12 requirements.

B-12 Data from Mozafar [1994] and Estimated Weights
of Plant Foods Required to Supply 2 Mcg of B-12


Mcg of B-12 per kilogram (dry wt.)

Amount of food necessary to achieve
2 mcg daily requirement of B-12

Dry wt.

Wet wt.















Barley kernels,






Barley kernels,


















*NOTE: Sprouting applies to the figures for soybeans and barley; spinach is eaten as-is.

See Appendix 5 for assumptions and technical notes regarding table derivation.

Analysis of Mozafar [1994] results

On the surface, the results of Mozafar [1994] appear to indicate that one may be able to get adequate B-12 from a diet of raw plant food. However, let's take a closer look at the numbers.

Soybeans. Soybeans in their crude form are inedible, and need sprouting or cooking to be rendered edible. Many raw-fooders would challenge the idea that even raw, sprouted soybeans are actually that edible, however, as the flavor is--how to say it--"intensely awful." At any rate, to satisfy B-12 requirements one must eat 2.64-4.78 kg, or 5.81-10.52 pounds of soybean sprouts, per day, to meet B-12 requirements. It is very difficult/nearly impossible to eat that much bulk on a regular basis. The crude beans (0.75-1.37 kg) can be cooked, and the bulk is more manageable, but it is not clear how much extra one would need to eat to adjust for B-12 losses in cooking.

Barley kernels. Barley kernels in their crude form are inedible. While not 100% certain, it appears Mozafar tested unhulled barley, which has a tough hull (with sharp edges when chewed) that makes eating it raw very difficult, even when sprouted. The amounts of barley required are lower than for soybeans; in sprouted form, the estimate is 0.49-1.70 kg, or 1.07-3.74 pounds. However, the reality of the extremely tough hull on barley makes eating even 0.49 kg (1.07 pounds) per day a difficult and unpleasant task. The 0.24-0.85 kg (0.53-1.87 pounds) of crude barley kernels, if hulled and cooked, are easy to consume. Again, the problem arises in that one needs accurate data on B-12 losses in cooking to know how much extra to eat to compensate for loss of B-12 in cooking.

Spinach. Here 1.33-3.44 kg (2.94-7.57 pounds) are required. The amounts are within the range of possibility for a person to eat, though it would be difficult (bulk--multiple meals required). The problem, of course, is that a reliable supply of manured spinach is not available to most people, and the weights required of control (unmanured) spinach--3.44 kg or 7.57 pounds--are far too high, again, i.e, yet another bulk problem. It would be extremely difficult to eat that weight of greens in a day.

Comments on the Mozafar [1994] research

Research needs to be repeated and verified. The Mozafar paper is the first paper to report B-12 levels above trace in common plant foods. As it is but one study, the research needs to be validated--i.e., it should be repeated and extended by others. (Repetition of the research would provide important confirmation information.) It would be interesting to include root crops, fruit, and wheat in any future research along these lines; indeed, the extension of Mozafar's research to woody plants like tree and bush crops could be very important. Additional comments:

Geophagy: another source for B-12?

Warning: for some, this may be in poor taste too. (But remember here our goal to be as thorough as possible on the topic.)

Chimps and other apes have been observed engaging in geophagy, i.e., eating dirt, though the predominant hypothesis is that chimp geophagy is done to ingest clay that absorbs excess plant tannins in the GI tract (and not as a B-12 source).

Mozafar [1994] reports 14 mcg B-12 per kg of soil. If we assume this is all true B-12 and no analogues (highly unlikely), it implies a daily intake of ~143 g (0.31 pounds) of soil daily to satisfy B-12 requirements. Such an intake is obviously not feasible. Note that Mozafar lists B-12 values for soil from other studies as well (Table 3, p. 309, Mozafar [1994]). However, many of the studies cited are old and thus the assay methods used should be checked. Mozafar reports that soil is one of the richest sources of B-12, but that there is no information available on the level of analogues vs. true B-12 in soil.

Synopsis of impact of Mozafar research

The Mozafar research provides a limited confirmation of the earlier research by Halsted (as reported in Herbert [1988]). That is, if you eat enough plant foods grown in manured soil, you might get adequate B-12. However, inasmuch as most of us buy our foods from markets, it would be unsafe to assume that a typical raw/vegan diet provides adequate B-12. Accordingly, the use of B-12 supplements (and/or supplemented foods) by vegans is still appropriate.


(Feasible Vitamin B-12 Sources in Evolution / Mercury and B-12)

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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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