DIETARY SOY PROTEIN ISOLATE, COMPARED WITH CASEIN, REDUCES ATHEROSCLEROTIC LESION AREA IN APOLIPOPROTEIN E-DEFICIENT MICE

The objective of this study was to compare the effects of dietary soy protein isolate and casein on atherosclerotic lesion development in ap olipoprotein (apo) E-deficient mice. Male C57BL/6J apoE-deficient mice (9-10 wk old) in groups of 6-9 were used in a series of feeding studi es. In the first experiment, mice were fed purified diets containing c holesterol (1 g/100 g) and cholate (0.25 g/100 g) for 6 wk; soy protei n isolate or casein was used as the protein source. Although serum tot al cholesterol concentration did not differ between groups, the lesion area of the thoracic aorta in the soy protein isolate group was lower than that of the casein group (P < 0.01). In the second and third exp eriments, mice were fed the same purified diet as in Experiment 1, onl y without supplementation of cholesterol and cholate for 24 and 9 wk, respectively. In each of these two experiments, serum total cholestero l concentrations again did not differ between soy protein isolate- and casein-fed groups. Serum homocysteine concentrations did not differ b etween groups in Experiment 3. Dietary soy protein isolate, compared w ith casein, lowered the thoracic aorta lesion area (Experiment 2; P < 0.001) and the percentage of the aortic arch inner surface covered by lesions (P < 0.05). In the final experiment, mice were fed the cholest erol-free diets containing ethanol-extracted soy protein isolate or ca sein plus the soy protein ethanol extracts for 9 wk. There were no dif ferences in serum total cholesterol concentration or thoracic aorta le sion areas between the two groups. These results indicate that the ant iatherogenic effect of native soy protein isolate cannot be explained by its effect on serum lipids or homocysteine and suggest that both th e protein component and the ethanol extracts of the soy protein isolat e may contribute to the antiatherogenic effect of the native soy prote in isolate.