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1 From the Tufts University Schools of Medicine and Nutrition and the Frances Stern Nutrition Center, New England Medical Center, Boston.
2 Supported in part by contract number 53/3 K06-10 with the US Department of Agriculture.
3 Address reprint requests to JT Dwyer, Frances Stern Nutrition Center, New England Medical Center, Box 783, 750 Washington Street, Boston, MA 02111. E-mail: johanna.dwyer{at}es.nemc.org.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONPERSPECTIVES ON VARIOUS EATING...IS THERE A CONVERGENCE...ARE WE IN THE...REFERENCES |
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Key Words: Vegetarian diet • plant-rich diet • plant-only diet • vegan diet • macrobiotic diet • omnivorous diet • dietary guidelines
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INTRODUCTION |
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PERSPECTIVES ON VARIOUS EATING PATTERNS |
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Timothy Key asserted that habit, tradition, food availability, and the influences of advertising determine the food choices of most people, but that food choices should instead be based on scientific, environmental, ecologic, and nutritional considerations. He advocated more strenuous efforts to disseminate nutrition recommendations widely via the mass media, which could lead to changes in national attitudes and personal food choices that are based more on nutritional considerations. Key saw the most likely movement at the national level to be toward plant-based rather than plant-only diets. He pointed out that the literature on the long-term health of vegans was meager and that more research was needed because existing studies were based on small numbers of individuals. Key called for more research on vegan diets, especially those given to children. He also recommended more research on vegetarian and semivegetarian diets in highly industrialized countries. Much more is known about semivegetarian diets and their association with health in developing countries.
Macrobiotic perspectives
Lawrence Kushi said that the general principle behind the macrobiotic diet is that foods biologically far away from humans are better for humans, so those foods, rather than red meat, should form the basis of the diet. Kushi opined that there was a bias in the scientific literature against macrobiotics. When findings were negative, the word macrobiotic appeared in the title, whereas when findings were positive, the word vegetarian was used. Kushi noted that some health problems such as rickets, borderline vitamin B-12 deficiency, and risks of other deficiencies had existed in the past when young children were fed some macrobiotic diets. He believes that this is no longer true and that macrobiotic parents have altered their infant feeding practices. With respect to health benefits, macrobiotic lifestyles appear to be associated with decreased blood cholesterol and blood pressure, and possibly beneficial changes in some serum estrogen subfractions that may be associated with lower cancer risk.
Lactoovovegetarian perspectives
David Nieman cited results of the Adventist Health Study and of many other studies showing that long-term lactoovovegetarians who had adhered to their diets for decades weighed less, had lower total serum cholesterol and blood glucose concentrations, and had lower blood pressure than did nonvegetarians. He summarized evidence showing that increased consumption of fruit, vegetables, and dietary fiber appeared to be associated with lower rates of coronary artery disease and stroke even in those who consumed some animal foods, especially if they included fish and very lean meat. On balance, Nieman added that there was solid evidence that lactoovovegetarians have lower prevalence rates of ischemic heart disease, type 2 diabetes, obesity, hypertension, dyslipidemia, and possibly some forms of cancer (eg, breast and colon) than do omnivores, and that diet was at least partly responsible for these findings. However, the vegetarian diet is "only one spoke in the wheel that turns toward wellness." Vegetarians are often more physically active than are omnivores; thus, they also benefit from the many positive effects of active lifestyles.
Sujatha Rajaram spoke about the need for those following vegan diets to guard against dietary inadequacies through careful dietary planning. She emphasized the importance of eating plant-based diets that are high in whole grains rather than highly processed or refined foods. Such whole-grain foods have the advantage of being high in fiber, rich in antioxidant nutrients and phytochemicals, and low in fat. These dietary constituents reduce the risk of certain diet-related, chronic, degenerative diseases, such as coronary artery disease. Unsupplemented whole-food diets based solely on plants are not appropriate because they are devoid of vitamin B-12. Low concentrations of vitamin B-12 are apparent in the sera of individuals who consume such diets, especially after they have consumed such diets for many years. Vitamin B-12 deficiency is a special problem for pregnant vegans unless they are supplemented. Another nutrient that tends to be low in plant-only diets is calcium; plant foods must be chosen carefully to obtain enough calcium from them. Consumption of tofu and calcium-fortified orange juice helps. Vitamin D is a concern for vegans chiefly in wintertime and in northern latitudes where there is little sunlight. Vitamin D–fortified milk or vitamin D supplements are recommended for vegans. Consuming enough iron is sometimes a problem for vegans, but wise food choices or iron supplements can remedy the situation. Rajaram recommends a lactovegetarian diet, especially one that stresses whole foods and low-fat milk products.
Omnivorous perspective
Walter Willett spoke about plant-based omnivorous diets, of which there are many in the world. Both Greek and Japanese eating patterns appear to offer advantages in these respects over certain other patterns. The challenge is to find out what components are responsible for beneficial effects in both vegetarian and omnivorous dietary patterns. Inappropriate choices within vegetarian or nonvegetarian diets can lead to health problems. Willett discussed unresolved questions about diet and breast cancer. He concluded that even though, on average, vegetarian diets are quite healthy, there may be ways to improve them even further. Research is needed on these issues.
Audience perspectives
Among the concerns of the audience was whether genetic alterations taking place in the plant-food supply would affect the health of vegetarians or vegans. The panelists recalled that selective breeding has been practiced for thousands of years, but stressed that caution was indicated so that biotechnology would be used appropriately. An audience member urged more emphasis on ecologic and environmental concerns relating to food and eating patterns; to "take the global viewpoint on resource use." Another audience member asked whether it was better to add phytochemicals to milk or to add vitamin B-12 to soyfoods. The issue was left unresolved by the panel. The next question concerned how much meat semivegetarians should eat for optimal health, and whether 1–2 servings/wk would be optimal. A panelist suggested that the National Academy of Sciences recommends a larger amount. Other questions concerned whether vegetarians should become even more physically active (the panelists agreed that this was helpful) and a plea to be more specific about how vegetarian diets reduce disease risks in discussions of diet and health.
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IS THERE A CONVERGENCE OF SCIENTIFIC OPINION ON PLANT-BASED AND PLANT-ONLY DIETS? |
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From the education and communications standpoint, there is convergence in that the information disseminated on nutritious diets is sounder, more sophisticated, and more plentiful than ever before. The negativism and ridicule that vegetarians were once subjected to in the popular press has also largely disappeared. The media are increasingly tolerant and accepting of vegetarian and a variety of omnivorous patterns.
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ARE WE IN THE MIDST OF A "PARADIGM SHIFT?" |
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Until the 1950s, adequacy and prevention of deficiency diseases was the main criterion and the standard for judging the healthfulness of dietary patterns. It is now well established that plant diets can be made adequate in the nutrients they lack by complementation, fortification, and supplementation, so these are hardly breakthroughs in thinking that would constitute a paradigm shift. It is also evident that variety does not need to be limited on vegetarian diets, and that balance and moderation can be achieved as easily, or even more easily, with vegetarian than in omnivorous dietary patterns.
Today, our criteria for salubrious dietary patterns are broader than nutritional adequacy and avoidance of deficiency disease. They include balance, moderation, and a focus on reducing the risks of chronic degenerative diseases. Improvements in analytic equipment and techniques have permitted an expansion of research on how chemical differences between various types of dietary patterns are related to health benefits (Dwyer JT, Redican S, unpublished observations, 1997). If a paradigm shift has occurred in scientists' views of dietary patterns, it is in 2 areas. First is the recognition that essential nutrients can be added to plant foods. From a technical standpoint, a greater variety of plant foods; more plant foods fortified with vitamins B-12 and D, iron, and calcium; and more nutrient supplements are available today than ever before. These developments mean that convergence between the essential nutrient profiles of plant-only and plant-based eating patterns is possible if vegetarians use these expanded options in dietary planning (5). Second is the recognition that diet affects chronic degenerative disease risk and that many chemicals other than nutrients in foods are important to health. It is important to continue research on how dietary patterns vary in their composition of nonnutrient substances in foods that affect health.
Remaining divergence in values about eating
Both scientific issues and values are involved in scientists' nutritional recommendations. Values are not amenable to verification by empirical methods (5, 6). For most eaters, choices between the various types of patterns are matters of taste, not of health or morality. Not everyone in society agrees that there are moral imperatives for following a particular eating pattern. In any event, ethical, religious, and moral considerations remain personal and beyond the scope of science to dictate. For others, such as some vegans, moral judgements and principles, nutrition, and health all play a part in eating decisions (6). Individual eaters make different choices and rationalize them differently. There is little evidence that societal or individual philosophies, ideologies, and tastes are converging to favor a single eating pattern to guide food choices among the multiple patterns discussed. Moreover, attempts to force such a convergence may do more harm than good. The prescription of a single pattern that everyone should follow is not only beyond the scientific evidence; from a practical standpoint, it will surely fail.
The progress of science and the passage to dietetic perfection
Does nutrition science progress and evolve over time toward dietetic perfection? Certainly, nutrition has advanced from primitive to more complex and elaborate elucidations of the health effects of what we eat. Science works best within a dominant paradigm that endures until it is replaced by a single new paradigm. Nutritional guidance is different. It needs to be based on science, but there is plenty of room for diversity. Scientific progress should not be interpreted to imply that each successive breakthrough in nutrition knowledge brings us closer to a single platonic eating ideal or to "dietetic truth." Scientists must continue to respect dietary freedom and diversity when making recommendations. They must continue to resist "nutritional imperialism" that insists on a single recommended eating pattern, be it vegetarian or omnivorous. Dietary diversity is one of our culture's strengths and sources of pleasure. There are many healthy ways to eat to be healthy, happy, and wise.
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REFERENCES |
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This article has been cited by other articles:
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  E. Lea, A. Worsley, and D. Crawford Australian Adult Consumers' Beliefs About Plant Foods: A Qualitative Study Health Educ Behav, December 1, 2005; 32(6): 795 - 808. [Abstract] [PDF]
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 C. Koebnick, A. L. Garcia, P. C. Dagnelie, C. Strassner, J. Lindemans, N. Katz, C. Leitzmann, and I. Hoffmann Long-Term Consumption of a Raw Food Diet Is Associated with Favorable Serum LDL Cholesterol and Triglycerides but Also with Elevated Plasma Homocysteine and Low Serum HDL Cholesterol in Humans,2 J. Nutr., October 1, 2005; 135(10): 2372 - 2378. [Abstract] [Full Text] [PDF]
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S. P. Murphy and L. H. Allen Nutritional Importance of Animal Source Foods J. Nutr., November 1, 2003; 133(11): 3932S - 3935. [Abstract] [Full Text] [PDF]
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 R. Weinsier Use of the term vegetarian Am. J. Clinical Nutrition, May 1, 2000; 71(5): 1211 - 1212. [Full Text] [PDF]
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