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Department of Nutrition, School of Public Health, Loma Linda University, Loma Linda, CA 92350, E-mail: pjohnston{at}sph.llu.edu
Dear Sir:
We agree with Weinsier regarding the use of the term vegetarian. In fact, we raised the very same issue in another forum some 5 y ago (J Sabaté, unpublished observations, 1994). We proposed then that the criteria for defining a vegetarian diet place more emphasis on the presence of vegetables, fruit, grains, and other plant foods and less on the absence of flesh products from the diet. We suggested that the cutoff points between what have been called vegetarian, semivegetarian, or nonvegetarian diets not be based solely on the frequency of meat consumption, as is usually the case in research studies. Further, we suggested that persons who do not have ample daily consumption of fruits, vegetables, and whole-grain cereals be considered nonvegetarians, regardless of their consumption of meat and other animal products. Such classification is intended to give credit to the potential health effects of plant foods rather than to emphasize only the effects of meat.
As noted by Willett (1) in the keynote address at the Third International Congress on Vegetarian Nutrition, there has been a shift in thinking in the past decade regarding vegetarian diets. In the past, the focus was on foods that were excluded from the diet, particularly meat, and the attendant health effects. More recently, attention has focused on the benefits of some foods, such as fruit and vegetables, that may be found in larger quantities in vegetarian diets. The point has been well made that vegetarian diets may or may not be healthful (1). Further, depending on food choices, an omnivorous diet may prove to be equally healthful (2).
Problems in both terminology and complexity are encountered in studies designed to ferret out relations between diet and health. The dietary intake patterns of persons calling themselves vegetarians are as diverse as are the patterns of persons who are classified as omnivores. Very little can be correctly assumed about nutrient intake from the use of either term or from the various other terms that have been used in an attempt to be more descriptive of particular dietary patterns. It has been repeatedly stated that to evaluate the nutritional adequacy of a vegetarian diet, a detailed dietary intake record must be obtained (3). In addition, other lifestyle-related practices need to be assessed for their relevance to nutritional status (4).
Scientists can attempt to evaluate the health effects of nutrients, foods, or dietary patterns. As we progress from a single nutrient to overall dietary patterns, analytic complexity increases greatly. Describing the effect of a single nutrient is much less challenging than describing the effects of the mixture of foods consumed in often varying amounts as part of any diet. In addition, persons who follow distinct dietary patterns often have other lifestyle characteristics that have various health effects that may confound the effects due to diet. This challenge is not unique to researchers studying vegetarian diets but has been encountered in studies of the now well-publicized Mediterranean diet (5). The inclusion of philosophic considerations associated with dietary patterns adds another layer of obstacles to be overcome in understanding the true relations of dietary intake to health outcomes.
Another problem encountered with some frequency is the attribution of outcomes from a diet that has been classified as vegetarian to another diet for which the same terminology is used but that is quite different in the foods that are included and excluded. As a result, nutritional problems encountered in persons who follow a particular vegetarian diet have been attributed to all persons who call themselves vegetarians. Conversely, the beneficial effects associated with some vegetarian dietary practices may be attributed inappropriately to all so-called vegetarians.
Despite the fact that this issue of terminology was raised several years ago, the reality is that there is a tradition among both the public and researchers to continue to use vegetarian as a descriptor of dietary practices, even though this is a reductionistic approach to the naming of complex food patterns. As we continue to address this topic, it is doubtful that we will find one term that adequately differentiates the various dietary patterns often covered by the term vegetarian diet. It is necessary, then, within any given study, to describe with some care and precision the dietary characteristics that are being investigated. Nonetheless, we are comfortable with the use of the term plant-based diet to describe the dietary intake of the increasing number of persons who want to decrease their intakes of animal foods and replace them with plant foods.
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