There is strong evidence that dietary components, especially dietary fat, can exert a significant influence on risk factors for coronary heart disease (CHD). It is generally agreed that dietary intakes of saturated fat should decrease. Carbohydrate, monounsaturated fat and polyunsaturated fat have each been recommended to replace dietary saturated fat. Additional recommendations have been made to increase n3-fatty acid intake. We hypothesize that alterations in the dietary levels of specific classes of fatty acids (saturated, monounsaturated, polyunsaturated, and n-3 fatty acids) will have differential effects on known or suspected CHD risk factors; that for a population of subjects, specific recommendations regarding specific dietary fatty acid classes can be formulated which will minimize their apparent CHD risk, and that these recommendations will be unique for a given population and/or co-morbid condition. To test this hypothesis, we propose to examine the effects of series of dietary recommendations regarding fatty acid intake (reduction in SFA and total fat; replacement of SFA with either MUFA or PUFA; supplementation of diets with n3-fatty acids) on a constellation of known or suspected risk factors for CHD in a multiracial population of men and women. The risk factors which we propose to examine include: 1) plasma lipid, lipoprotein, and apolipoprotein levels; 2) lipoprotein composition; 3) LDL and HDL subpopulation distribution; 4) susceptibility of LDL to oxidative modification; 5) indices of eicosanoid metabolism; and 6) insulin resistance. Finally, we propose to further examine two diets identified in the above studies for their effectiveness in reducing CHD risk in two additional populations of subjects which may differentially respond to the dietary modifications, older men and women and obese men and women.