DIETARY COMPOSITION, OBESITY, AND CARDIOVASCULAR RISK

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Coronary heart disease (CHD) is a major cause of death and disability in our society. Obesity increases CHD risk by adversely affecting glucose, lipoproteins, and blood pressure. There is consensus that dietary saturated fat and cholesterol (C) restriction is beneficial for low density lipoprotein (LDL) lowering and CHD risk reduction, but there controversy about other aspects of the diet. We propose to examine the effects of three diets meeting National Cholesterol Education program Step 2 diet criteria on body weight and composition and on CHD risk factors (LDL C, HDL C, remnant lipoprotein C, Lp(a) C, insulin, glycosylated hemoglobin, glucose, and blood pressure) in the fasting and nonfasting state (4 hours after a meal) in 80 men and women (men greater than or equal to 50 and less than 65 years of age, women postmenopausal and less than 65) with LDL C values greater than or equal to 130 mg/dI and a body mass index greater than or equal to 28 and less than 38 kg/m2. A four phase study will be conducted in which all food and drink is provided during the first 3 phases, while diet is recommended but not provided in the fourth phase. In phase 1, all subjects will initially be placed on an average isoweight U.S. diet for 5 weeks (15 percent protein, 35 percent fat; 15 percent saturated fat; 15 percent monounsaturated (mono) fat; 6 percent polyunsaturated (poly) fat, with 150 mg of cholesterol/1000 calories and 10 g/1000 cal. of fiber). For phase 2, subjects will then be equally randomized to one of 3 diets, all containing 15 percent protein, 5 percent saturated fat and 60 mg of cholesterol/1000 calories: 1) high complex carbohydrate (CHO): 15 percent fat, 5 percent mono, 5 percent poly, and 70 percent CHO (mainly complex with relatively high glycemic index), 16 g/1000 cal of fiber, and low dietary caloric density of 1.10 cal/gm; 2) high mono: identical to diet 1 except that the fat content will be 30 percent (15 percent mono) and 55 percent CHO with CHO of high glycemic index and high caloric density, 1.25 cal/gm; and 3) composite: identical to diet 2 except that there will be lower glycemic index and low dietary caloric density of 1.10 g/1000 cal). These diets will be given ad libitum, and subjects can adjust their calorie level using 200 calorie casseroles from 66 percent to 133 percent of calories needed to maintain weight, for a 12 week period. Subjects will then be continued on these same diets isoweight for an additional 5 weeks under controlled circumstances in phase 3, and then for one year (phase 4) under uncontrolled circumstances where they will receive dietary instruction and menus, but not food. Body weight and blood pressure will be assessed three times per week, and plasma lipoproteins (LDL, HDL, remnants, and Lp[a]), glucose, glycosylated hemoglobin, and insulin levels will be assessed three times in the fasting state and once in the fed state at the end of each controlled dietary period and at 3, 6, 9, and 12 months in the long-term follow-up period. In addition, body weight, body energy expenditure, physical activity, body composition, anthropometics, and metabolic rate will be measured at regular intervals during all phases. Our hypothesis is that the fat-restricted diet rich in complex carbohydrate and low in caloric density and the composite diet low in caloric density and glycemic index will have a more favorable effect on CHD risk factors, body weight, body composition and energy expenditure than the Step 2 diet higher in mono fat, glycemic index, and caloric density.