Diet is a component in the etiology of the two major causes of death in the United States, namely, cardiovascular disease and cancer. During the last decade, various organizations have suggested that we alter the“typical”American diet in order to decrease the incidence of these diseases even though both diseases are indisputably of multiple etiology. An implication behind these recommendations is that individuals will increase their longevity by changing their diets. The burden of proof falls on those proposing changes to the diet that such alterations will be safe and effective. In spite of our often indicted diet, mortality from heart disease and stroke continue to fall and deaths from diet-related cancers are static or dropping. Longevity in the U.S. is exceeded by only five countries, whose populations consume a diet similar to ours in four, and that in the fifth is approaching ours. While low-fat high-fiber diets probably have some beneficial effect vis-a-vis chronic diseases, it is likely that other risk factors contribute more to the total risk of disease. Therefore, it is illogical to expect dietary manipulation to offset significantly other concurrent risks such as heredity, tobacco use, hypertension, and obesity. Individuals who are at high risk for specific diseases should modify their diets to minimize this particular risk factor. Most Americans can safely reduce their intake of total calories, fat, sugar, and salt. Although this can be achieved most readily on a population basis by following a form of“prudent”diet, it is premature to promise medical benefits to individuals.(ABSTRACT TRUNCATED AT 250 WORDS)