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*Cancer Research Center of Hawaii, University of Hawaii, Honolulu, HI 96813 and Department of Nutrition, University of California, Davis, CA 95616
2 To whom correspondence should be addressed. E-mail: suzanne{at}crch.hawaii.edu.
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ABSTRACT |
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 TOP ABSTRACT LITERATURE CITED |
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KEY WORDS: • animal source foods • schoolers • dietary quality • micronutrients
Through choice or necessity, many people consume diets that contain few or no animal source foods (ASF)3. Both macronutrients and micronutrients may be present in suboptimal levels in primarily vegetarian diets (1–3); however, these diets are considered by many to be a healthy alternative to a more omnivorous diet that is high in saturated fat and cholesterol and low in fiber (4,5). Both lacto-ovo vegetarian and nonvegetarian diets can be nutritionally adequate, but considerable care must be taken with true vegan diets, which include no ASF. This article will discuss the advantages of combining plant-based diets with ASF.
Findings from the Nutrition Collaborative Research Support Program
The Nutrition Collaborative Research Support Program (NCRSP), conducted in the 1980s, identified a variety of micronutrients that were low in the diets of children in marginally malnourished regions of Kenya, Mexico and Egypt (6). In both Kenya and Mexico, the diets contained few animal products. Although protein intake appeared to be adequate for almost all children, even after adjustment for protein quality, the intake of several micronutrients was clearly low. Table 1 shows the estimated prevalence of inadequate intake by young children for six nutrients of particular concern: iron, zinc, vitamin B-12, riboflavin, calcium and vitamin A. Negative health outcomes are known to occur if intake of these nutrients is below requirements. These problems include anemia, diminished work capacity, night blindness and poor growth, as a result of moderate inadequacies. More severe problems can result from long-term low intake of these nutrients: rickets, impaired cognitive performance, blindness, neuromuscular deficits, psychiatric disorders and death.
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Nutrients in plant and animal source foods
The nutrient levels in several plant and animal source foods are compared in Table 2. Whether considered per unit of weight or per unit of energy, ASF tend to be richer sources of the six nutrients of concern. Not only are these foods high in many micronutrients, but the nutrients often are more available. Table 2 shows that both iron and zinc are more bioavailable in animal foods. In addition, the bioavailability of carotenoids as vitamin A precursors is now believed to be lower than indicated in traditional food composition tables (7). Thus, for diets that depend on plant sources of vitamin A, more fruits and vegetables are needed to meet requirements than was thought previously. In the case of vitamin B-12, all requirements must be met from ASF, as there is virtually no vitamin B-12 in plant source foods.
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ASF also tend to be sources of macronutrients that may not be desirable in the diet, such as saturated fat and cholesterol, although lean alternatives contain less of these macronutrients (Table 2). ASF also may be undesirably high in total fat, energy and protein. For children in developing countries, a concentrated source of these macronutrients often is desirable, although for children (and adults) in more affluent countries, excessive consumption of energy-dense foods may lead to overconsumption of energy. Although meat intake has been associated with an increased risk of colon cancer in several studies, processed meats appear to be stronger predictors than unprocessed meats (9). Particularly in developing countries, the contribution of meat to improved nutrient intake more than offsets this uncertain association with colon cancer (10,11).
Studies of the effects of vegetarian diets on nutrient intake and status
Dagnelie and colleagues have shown that Dutch infants consuming macrobiotic (strictly vegan) diets had poorer nutritional status and were more likely to have rickets and deficiencies of vitamin B-12 and iron (12,13). In Nepal, xeropthalmia in young children was less likely to occur if they had relatively high meat or fish intake when they were 13 to 24 mo of age (14). U.S. men consuming vegan diets had lower serum ferritin concentrations, and 10 of 25 vegans in the study had marginal deficits of vitamin B-12 (15). However, the vegan diets also tended to be lower in fat and higher in fiber, vitamin C, folate, magnesium, copper and manganese. Recently, Hunt (16) summarized studies of the iron and zinc status of vegetarians and expressed concern about mineral status for those consuming plant-based diets. The panel setting the new Dietary Reference Intakes for iron assumed 10% iron absorption for vegetarian diets versus 18% absorption for a mixed diet and thus suggested that the Recommended Dietary Allowance for iron should be 80% higher for vegetarians (7).
It is commonly assumed that vitamin B-12 deficiency is unlikely if small amounts of ASF are consumed. However, this is clearly not the case, as it is becoming clear that the prevalence of vitamin B-12 deficiency is very high in many poorer regions of the world, including Kenya (17), India (18), Guatemala (19) and Mexico (20). A number of studies now show the vitamin B-12 status of lacto-ovo vegetarians in industrialized countries to be considerably worse than that of omnivores (21, 22), presumably because of the lower amount of vitamin B-12 in milk than in meat.
Concern also has been expressed about the difficulty that children have in obtaining adequate energy and nutrient intake from bulky plant-based diets. Recent recommendations from the World Health Organization on complementary feeding demonstrate that only ASF have the potential to provide enough calcium, iron and zinc for infants (23).
Designing an intervention to provide ASF
We utilized information on the nutrient content of foods to design a snack to feed to school-age children in rural Kenya. It was hypothesized that children who received a combination of githeri (a local stew of maize, beans and vegetables) and either milk or beef would consume a more nutritionally adequate diet overall than children who received the same amount of energy from githeri alone and thus would perform better on a variety of health and performance measures. Table 3 shows the composition of the three snacks expressed as a percentage of a schooler's recommended intake. As expected, the two snacks containing ASF supplied a higher proportion of most nutrients than the vegetarian snack. When averaged across the eight nutrients in Table 3, the milk and beef snacks provided more than twice as great a proportion of the recommendations. Although a combination of both milk and meat plus githeri was not tested, it is clear from the data in Table 3 that the overall proportion of the recommended intake provided would have increased even more. Diets based on starchy staples other than maize (i.e., rice) would be improved equally by the addition of small amounts of ASF.
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Food guides
The Food Guide Pyramid (FGP) for the U.S. was developed to provide guidance to Americans on food choices that would provide a nutritionally adequate diet (24,25). It includes recommended amounts of meat or meat substitutes, and dairy products. Development of a vegetarian alternative to the FGP has proved to be difficult, because few plant source foods can provide meaningful levels of nutrients such as calcium. Furthermore, in a vegan diet with no animal products, a supplemental source of vitamin B-12 must be provided. Although a vegetarian equivalent to the FGP has recently been proposed (26), it relies on fortified foods to obtain adequate intakes of vitamin D, vitamin B-12 and calcium. Food guides for other countries usually include recommendations for both dairy and meat intakes (27).
Thus, the FGP recommendation to consume 2–3 servings of dairy products (where 1 cup of milk is a serving) and 5–7 ounces of lean meat or meat substitutes (where one-half cup of cooked dried beans, 1 egg or one-third cup of nuts counts as 1 ounce of meat) appears to be applicable to developing countries as well. Although the sources and amounts of these animal products may vary across cultures, the advice to include them in a healthy diet should be universally applicable.
Dietary quality
Dietary quality can be evaluated in a variety of ways. One of the easiest ways is to determine a mean proportion of nutrient recommendations that is supplied by the diet (as was done for the snacks for the Kenya study and shown in Table 3). This approach also could be used to evaluate the impact of including various amounts of ASF on overall nutrient adequacy, using a more extensive list of nutrients. However, a food-based dietary quality measure also has been utilized in scoring schemes such as the Healthy Eating Index (HEI) (28). This approach to determining dietary quality compares intakes of the five major food groups (grains, vegetables, fruit, dairy and meats) to those recommended by the FGP and assigns a score (e.g., zero for no intake of a food group and 10 for at least the recommended intake). The average score across the five groups then can be used to determine the overall dietary quality. In addition, the HEI scores intakes of total fat, saturated fat and cholesterol to provide measures of overconsumption. Such an evaluation scheme eliminates the need to utilize extensive food composition tables when determining overall dietary quality. Thus, an index like the HEI could provide a useful method of quickly evaluating dietary quality in both developing and developed countries. A diet with a high dietary quality score needs to include either dairy or meat products (or meat substitutes), but still be moderate in fat.
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FOOTNOTES |
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3 Abbreviations used: ASF, animal source foods; FGP, Food Guide Pyramid; HEI, Healthy Eating Index; NCRSP, Nutrition Collaborative Research Support Program.
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LITERATURE CITED |
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TOPABSTRACTLITERATURE CITED |
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