Several carefully studied populations in Mediterranean countries and in some areas in Asia where traditional diets consisted largely of foods of plant origin exhibit low rates of many chronic diseases and long life expectancies. Many case-control and prospective studies have provided further evidence that high consumption of plant foods confers numerous health benefits. Investigations support links between increased vegetable, fruit, and fiber consumption, and lower rates of several cancers, coronary heart disease (CHD), neural tube defects, and cataracts. Although the mechanisms are not fully understood, carotenoids, folic acid, and fiber, all abundant in the Mediterranean diet, appear to play important roles in prevention of these diseases. In contrast, much evidence suggests that high consumption of full-fat dairy products is likely to increase CHD risk. Epidemiologic studies have not provided evidence that high dairy product consumption by adults prevents fractures; in fact, the results of several studies suggest positive associations. Thus, the abundant fruit, vegetables, and whole grains, and the low to moderate intake of dairy products in traditional Mediterranean diets are likely to have contributed to the low rates of numerous chronic diseases observed in these populations.