ABSTRACT
OBJECTIVES: To determine whether, in individuals with hypercholesterolemia, substituting dietary soybean products for cows' milk products improves the plasma lipid profile and whether any change in the profile is due partially to soy oil. DESIGN: Randomized 3-treatment crossover trial. SETTING: Family practice clinics and an outpatient clinic in London, Ont. PARTICIPANTS: Seventeen healthy men and 17 healthy women with elevated plasma levels of total and low-density-lipoprotein (LDL) cholesterol and with normal plasma levels of triglycerides. INTERVENTIONS: Participants incorporated into their normal diet either 2% cows' milk products, soybean products or a combination of skim milk products and soy oil, each over period of 4 weeks, with 22-week wash-out periods. Plasma lipid profile, blood pressure and body weight were assessed after each dietary and wash-out period. OUTCOME MEASURES: Plasma levels of total and lipoprotein cholesterol, plasma levels of triglycerides, apolipoprotein B and A1 levels, blood pressure and plasma lipid peroxidation. RESULTS: The change in diet had no effect on body mass index, levels of apolipoproteins B and A1 and most plasma lipids. During the soybean period, the subjects' mean level of high-density-lipoprotein (HDL) cholesterol increased 9% (p < 0.04) and their mean LDL/HDL cholesterol ratio decreased 14% (p < 0.007). These effects were less pronounced during the skim milk/soy oil period. In the 24 subjects with the highest initial LDL cholesterol level and LDL/HDL cholesterol ratio, the mean LDL cholesterol level decreased 11% after the soybean period. In all subjects, changes in the LDL/HDL cholesterol ratio induced by a soybean diet were negatively correlated with the initial LDL/HDL cholesterol ratio and positively correlated with the initial HDL cholesterol level. CONCLUSIONS: In people with hypercholesterolemia, the plasma lipid profile improved after treatment with a soybean-product diet, and this improvement was partially due to soy oil. The degree of responsiveness was associated with initial risk factors for coronary artery disease.
