EFFECTS OF SUBSTITUTING DIETARY SOYBEAN PROTEIN AND OIL FOR MILK PROTEIN AND FAT IN SUBJECTS WITH HYPERCHOLESTEROLEMIA

Objectives: To determine whether, in individuals with hypercholesterol emia, substituting dietary soybean products for cows' milk products im proves 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 Lo ndon, Ont. Participants: Seventeen healthy men and 17 healthy women wi th elevated plasma levels of total and low-density-lipoprotein (LDL) c holesterol and with normal plasma levels of triglycerides. Interventio ns: Participants incorporated into their normal diet either 2% cows' m ilk products, soybean products or a combination of skim milk products and soy oil, each over period of 4 weeks, with 2 2-week wash-out perio ds. Plasma lipid profile, blood pressure and body weight were assessed after each dietary and wash-out period. Outcome measures: Plasma leve ls of total and lipoprotein cholesterol, plasma levels of triglyceride s, apolipoprotein B and Al levels, blood pressure and plasma lipid per oxidation. Results: The change in diet had no effect on body mass inde x, levels of apolipoproteins B and Al and most plasma lipids. During t he soybean period, the subjects' mean level of high-density-lipoprotei n (HDL) cholesterol increased 9% (p < 0.04) and their mean LDL/HDL cho lesterol ratio decreased 14% (p < 0.007). These effects were less pron ounced during the skim milk/soy oil period. In the 24 subjects with th e 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 ch olesterol ratio and positively correlated with the initial HDL cholest erol level. Conclusions: In people with hypercholesterolemia, the plas ma lipid profile improved after treatment with a soybean-product diet, and this improvement was partially due to soy oil. The degree of resp onsiveness was associated with initial risk factors for coronary arter y disease.