Toward more healthful dietary patterns--a matter of policy.

D i iet is a key determinant of health, as important a contributor to premature mortality as cigarette smoking.' The principles of diets that promote health and prevent disease are well established. First set forth 40 years ago by researchers concerned about rising rates of coronary heart disease,23 these principles are now thoroughly accepted as Federal nutrition policy4 and as national health objectives for reducing the risks of heart disease and other chronic diseases.5 Today's Dietary Guidelines for Americans advise variety in food intake; maintenance of healthy body weight; consumption of more grains, vegetables, and fruits but less fat, saturated fat, and cholesterol; use of sugar and salt in moderation; and use of alcohol in moderation, if at all.4 These guidelines are intended to be followed as a whole so as to constitute an overall pattern of dietary practices that promote health. The Department of Agriculture's (USDA) Food Guide Pyramid translates the guidelines into food choices, recommending that most daily choices come from grains, vegetables, and fruits ("plant foods"), fewer from meat and dairy foods ("animal foods"), and even fewer from fats and sweets.6 The benefits of following such a pattern are well supported by research. Largely plant-based diets are associated with protection against leading causes of death and disability, among them coronary heart disease, certain cancers, diabetes, stroke, digestive disorders, and other diet-related chronic conditions.i8 In recognition of such benefits, health agencies throughout the world have issued virtually identical sets of dietary recommendations.9 While authorities universally agree that largely plant-based diets promote good health, they differ on the extent to wvhich specific foods or nutrients affect disease risk. But because it is much easier to study the