The objective of the proposed studies is to assess, in older (40-70 years), hypercholesterolemic [low density lipoprotein (LDL) cholesterol 130-160 mg/dl] male subjects, the impact of consuming different sources of protein (mixed-animal versus soy) and/or different levels of isoflavonoids (primarily genestein and diadzein) on the concentration of plasma lipids [total cholesterol, very low density lipoprotein cholesterol, LDL cholesterol, high density lipoprotein cholesterol, triglyceride] and apolipoproteins (apo) [apo A-1, apo B, Lp (a)]; as well as isoflavonoids in plasma and urine; and hormonal status. The experimental design consists of two multi- phased studies devised to determine the independent effects of type of protein and/or level of isoflavonoids; in Study 1, within the context of a diet approximating that currently consumed in the U.S. [15 energy (E) % protein, 47 E% carbohydrate, 38 E% fat (15 E% SFA, 14 E% UFA, 6 E% PUFA), 170 mg cholesterol/1000 kcal] and Study 2, within the context of a diet consistent with recommendations for individuals with moderate hypercholesterolemia (Step 2 diet) [15 E% protein, 49 #% carbohydrate, 24 E% fat (7 E% SFA, 7 E% MUFA, 8 E% PUFA), 61 mg cholesterol/1,000 kcal]. The variable components of the diets, type of protein and isoflavoniods, will respectively comprise two-thirds (67%) of the protein of 10% of energy, and range from 3 to 49 mg/1000 kcal. The aims of the study are to determine the effect of 1) a one to one (E/E) substitution of soy for mixed-animal protein on plasma lipoprotein, on plasma lipoprotein patterns associated with CHD risk; 3) increasing the isoflavonoid content of the diet in a dose-related manner on plasma lipoprotein patterns associated with CHD risk; 4) dietary protein source on hormonal status (androgens, estrogens, thyroid); and 5) dietary isoflavonoids on hormonal status (androgens, estrogens, thyroid). The area of soy protein and isoflavonoids is highly controversial and in the public domain. The results of these studies, whether positive or negative, should contribute to the data base on which to formulate more specific public health recommendations with respect to decreasing risk of developing CHD.