Supplementing Vegetarian Diets

This section is compiled by Frank M. Painter, D.C.
Send all comments or additions to:    Frankp@chiro.org

From The October 2000 Issue of Nutrition Science News

by Charles K. Rosenberg, C.N.

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Vegetarians vary by degree, but all those who avoid animal products potentially lack some nutrients necessary for optimal living.

Vegetarian diets have blossomed and proliferated far beyond their countercultural roots in the early 1970s. Scientific evidence now makes clear that eliminating meat from the diet can indeed be a healthy choice. In fact, switching to a high intake of plant foods will provide the body with substantial amounts of vitamins, minerals and phytochemicals and low amounts of saturated fat—factors that have been associated with reduced risk of chronic diseases such as cancer and heart disease. [1] During the last 30 years, interest in such plant-based diets has shifted from assessing their adequacy to determining their specific health benefits. [2] And although scientists agree that there are a number of advantages, many also feel that, under certain circumstances, vegetarians may not be getting enough of a handful of nutrients.

Nutrient supplementation for some vegetarians is a necessary step for maintaining health, but choosing the right products can be a challenge. Unfortunately, despite an abundance of information in the scientific realm, there is little guidance in the popular literature. The opposite is true for many commercial diets, which often market an accompanying array of supplements. For example, if your customers know their blood type they can choose a multivitamin and an herbal combination to supplement their diets. If they follow Barry Sears' Zone diet, a range of products exists to help them along.

There are four significant types of plant-based diets in the Western world: lactoovovegetarianism, the vegan diet, macrobiotics and the raw-food diet (see sidebar for definitions). Those practicing these vegetarian diet variations may have to dig a little deeper to discover the supplements needed for an optimized diet. A good place to start, though, is with vitamin B12, calcium and vitamin D and, for premenopausal women, iron.

Vitamin B₁₂ (cobalamin), of all the micronutrients, is the one that vegetarians should pay the most attention to. Insufficiencies of B12 have been reported in lactoovovegetarians, in those on macrobiotic diets and in vegans, despite the consumption of foods believed to contain high levels of this vitamin. [3,4] A deficiency of this sort can be caused by a number of factors including reduced absorptive ability regardless of the amount of B12 in the diet. This occurs in a small percentage of people whose stomachs do not produce intrinsic factor, an essential compound that the human body produces for B12 absorption. However, the great majority of B12 insufficiencies in vegetarians can be attributed to dietary inadequacies.

Vitamin B12 is produced by bacteria, especially strains that live in soil. When animals ingest these bacteria through plant consumption, B12 is stored in their flesh. Thus, the best sources of vitamin B12 are animal flesh foods. Forms of B12 do exist in vegetable foods such as bacterially fermented soy foods and some algae and seaweeds that have surface bacteria. Nevertheless, much of the B12 in these foods exists in the form of a noncobalamin analog, which does not function in the same way that the true vitamin B12 does. [4-6 ]

Lactoovovegetarians often mistakenly believe that they are protected from B12 insufficiencies because the vitamin occurs in its absorbable form in eggs and dairy foods. For example, in a study of two groups of Seventh-day Adventist men—one lactoovovegetarian and the other vegan—both had a significantly lower serum concentration of B12 than a control group that ate one or more servings of animal-flesh foods per week. Dietary deficiency was implicated in 70 percent of the cases of inadeqate B12 status. Interestingly, there were no significant differences in B12 concentrations between the
lactoovovegetarian and vegan groups. [7] One explanation for these low B12 levels is that vegetarians tend to have a high fiber intake, which can reduce absorption of B12. [8] Because of this, all vegetarians should consume a form of cobalamin B12 supplementation such as from fortified soymilk or a multivitamin.

Calcium is often an issue for those on plant-based diets. Excessive protein in the diet, typical of omnivorous American diets, has been found to increase the amount of calcium excreted in the urine. Therefore, since vegetarian protein intake is generally lower than that of omnivores, lactoovovegetarians may not need as much calcium. But vegans and raw foods dieters, lacking dairy in the diet, may not have enough concentrated sources of calcium. And, although their calcium need may not be as great since their protein intake is less, some of the calcium in the vegan/raw foods diets may not be absorbed by the body. This is because of the potentially high amounts of phytate and oxalate, organic acids acting as precipitating agents, that bind to calcium and make it unavailable.

If vegetarians rely too heavily on spinach, whole beans (pinto, red, white) and whole grains, they may decrease calcium absorption, although this effect may be offset by the concomitantly high levels of calcium in a well-designed vegetarian diet. [9,10] Fortunately, vegans and raw foods dieters can rely on calcium-rich, low phytate and oxalate vegetables for much of their calcium. The best choices are broccoli, kale and Chinese greens such as bok choy and mustard greens. But steaming up a pot of greens is not as easy as pouring a glass of milk. For the vegan who can't get enough greens in the diet, calcium-fortified soymilk or calcium supplements are a must. A supplement that provides 500 to 1,000 mg of calcium in the well-absorbed citrate or citrate-malate form is also recommended.

Additional dietary factors that affect calcium retention are salt and caffeine intake. Like protein, excess salt increases urinary calcium loss. The same is true for caffeine, but to a lesser degree. Both vegetarians and omnivores should have no more than a moderate intake of sodium and caffeine. [10]

Vitamin D intake, as well as sufficient calcium, contributes mightily to bone health. Moreover, the high fiber content of plant-based diets can compromise vitamin D intake, since fiber binds with vitamin D in the digestive tract and reduces its absorbability. [11 ]

Vitamin D consumption is not usually a problem for lactoovovegetarians since most milk is fortified with this nutrient. Likewise, those individuals practicing macrobiotics who eat fish regularly ingest enough vitamin D. Even most vegans and raw foods dieters can get a sufficient quantity from exposure to sunlight; however, those living in northern latitudes may wish to consider supplements during the winter months when sun exposure is lowest.

Iron, particularly non-heme iron—the type found in vegetables—is less well-absorbed than the heme iron found in meat. In addition, the same vegetable phytates that bind with calcium and prevent its absorption can also do the same with iron. These factors suggest that a vegetarian diet would give rise to an iron deficiency but, surprisingly, deficiency is rarely seen in vegetarians. This is because humans have an internal regulatory mechanism to control the absorption and storage of iron. Although vegetarians have a significantly lower absorption of iron compared to omnivores, they balance this low absorption with a decrease of iron excretion in the feces. In other words, vegetarians hold on to the iron they do absorb. Omnivores, on the other hand, excrete more iron in response to their higher dietary intakes of this mineral. [12]

The internal regulatory mechanism of iron helps maintain bodily stores, at least in the short term, even in the presence of low dietary iron. However, scientists are still unsure about iron storage in those who are on plant-based diets for extended periods of time. Some suggest supplementation, but this may only lead to greater excretion. Nonetheless, supplementation may be wise, especially for premenopausal vegan women and any vegetarians who have maintained a meat-free diet for more than six years. [13 ]Men, postmenopausal women, vegans and raw foods dieters, however, should be careful of supplemental iron. No studies state these groups need extra iron, and iron overload in these populations may be a risk factor for heart disease. [For more information on iron, see NSN 2000 Jun;5(6):236-40.]

Vegetarian diets provide enormous health benefits by reducing the risk of disease and improving well-being. Despite the overall benefits, however, the chances of deficiencies of the nutrients discussed above are greater in vegetarians than omnivores. The perfect diet, plant-based or omnivorous, still eludes us. In the meantime, fortification and supplementation bring us a step closer.

Note: The dietary recommendations discussed above apply to non-pregnant adults. Nutritional needs of children on vegetarian diets should be reviewed by a certified nutritionist or other health professional.

Sidebars:

Vegetarians, Essential Fatty Acids And DHA

Glossary Of Diets

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Charles K. Rosenberg, C.N., is an adjunct faculty member at Bastyr University in Bothell, Wash.

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References:

1. Nestle M. Animal v. plant foods in human diets and health: is the historical record unequivocal? Proc Nutr Soc 1999 May;58(2):211-8.

2. Sabate J. Publication trends of vegetarian nutrition articles in biomedical literature, 1966-1995. Am J Clin Nutr 1999 Sep;70(3 Suppl):601S-7S.

3. Miller DR. Vitamin B-12 status in a macrobiotic community. Am J Clin Nutr 1991 Feb;53(2):524-9.

4. Dagnelie PC. Vitamin B-12 from algae appears not to be bioavailable. Am J Clin Nutr 1991 Mar;53(3):695-7.

5. Watanabe F. Pseudovitamin B (12) is the predominant cobamide of an algal health food, spirulina tablets. J Agric Food Chem 1999 Nov;47(11):4736-41.

6. Dagnelie PC. Some algae are potentially adequate sources of vitamin B-12 for vegans/comments on the paper by Rauma et al. (1995). J Nutr 1997 Feb;127(2):379.

7. Hokin BD. Cyanocobalamin (vitamin B-12) status in Seventh-day Adventist ministers in Australia. Am J Clin Nutr 1999 Sep;70(3 Suppl):576S-8S.

8. Linder MC. Nutrition and metabolism of vitamins. In: Linder MC, editor. Nutritional biochemistry and metabolism. 2nd ed. Norwalk CT: Appleton & Lange; 1991. p. 139.

9. Weaver CM. Dietary calcium: adequacy of a vegetarian diet. Am J Clin Nutr 1994 May;59(5 Suppl):1238S-41S.

10. Weaver CM. Choices for achieving adequate dietary calcium with a vegetarian diet. Am J Clin Nutr 1999 Sep;70(3 Suppl):543S-8S.

11. Lamberg-Allardt C. Low serum 25-hydroxyvitamin D concentrations and secondary hyperparathyroidism in middle-aged white strict vegetarians. Am J Clin Nutr 1993 Nov;58(5):684-9.

12. Hunt JR. Nonheme-iron absorption, fecal ferritin excretion, and blood indexes of iron status in women consuming controlled lactoovovegetarian diets for 8 wk. Am J Clin Nutr 1999 May;69(5):944-52.

13. Shaw NS. A vegetarian diet rich in soybean products compromises iron status in young students. J Nutr 1995 Feb;125(2):212-9

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