A solid foundation of epidemiologic, clinical and laboratory evidence underlies the current dietary recommendations for population-based prevention of coronary heart disease. Average blood cholesterol levels will decline with the consumption of less saturated fat and cholesterol than has been traditional in the United States. It is not clear, however, whether reductions in total fat intake are necessary as well. More research also is needed to define how best to provide a national food supply whose composition will enhance efforts to reduce coronary heart disease risk. Fatty acid investigations are especially critical, because this is an area in which the food industry has greater latitude in reformulating products according to current scientific evidence, dietary recommendations, and customer demand. Stearic acid, for example, may be suitable as a replacement for 'hard' fatty acids because it has relatively little effect on total blood cholesterol levels, but it may be rendered less suitable for this purpose if it accelerates the tendency of blood to clot. Similarly, hydrogenated vegetable oils are used as substitutes for saturated animal fats, but they contain trans-fatty acids that may raise low-density lipoprotein levels as do saturated fatty acids. In general, the mechanisms by which diet influences the eventual development of atherosclerosis through alterations in lipid and lipoprotein levels and metabolism, and through other factors such as hemostasis, still are not fully understood.