The results of large prospective epidemiologic investigations support the hypothesis that coronary disease risk depends on the quality rather than quantity of dietary fat. Whereas saturated fat and cholesterol appear to increase the risk of coronary heart disease (CHD) as predicted by their effects on blood lipids, strong evidence has emerged that the deleterious effects of trans unsaturated fatty acids (trans fatty acids) extend beyond those predicted by their well-known adverse influence on the ratio of low-density lipoprotein to high-density lipoprotein cholesterol. On the other hand, increased consumption of the polyunsaturated fats, linoleic acid and linolenic acid, appears to reduce the risk of CHD.