ANIMAL AND HUMAN STUDIES ON THE ROLE OF SOYBEAN, RICE AND NUTS CONSUMPTION IN HYPERCHOLESTEROLEMIA AND ATHEROSCLEROSIS

Soybean, rice and nuts are the staple foods in South East Asia. In order to clarify the function of these foods in relation to coronary heart diseases, we have done a series of experiments using animals and humans. Soybean protein preparations (SPI) in comparison with an animal protein, casein (CAS), resulted in reducing atherosclerotic lesion development in apolipoprotein (apo) E deficient mice that develop an advanced lesion similar to that in humans. This action was attributed to the protein, since the ethanol-extracted SPI (EE-SPI), from which isoflavones and saponins removed, lowered the lesion development in apo E-deficient mice. However, The EE-SPI, compared to the SPI, resulted in a decrease of mRNA for key proteins of cholesterol metabolism (low density lipoprotein receptor and cholesterol 7$\alpha$-hydroxylase) in hypercholesterolemic rats, followed by an elevation of the serum cholesterol level, indicating a contribution of isoflavones to the serum cholesterol level. Rice protein (RPI) was also effective to lower the lesion development in apo E deficient mice. Both the SPI and RPI led to an increased level of the serum NOiN03, metabolites of NO. This effect appeared to be attributed to their high content of arginine. Besides, C57BL/6J mice fed a diet containing whole grain rice had an elevation of the serum high-density lipoprotein cholesterol. Furthermore, rice bran oil and the unsaponifiable fraction that is rich in plant sterols were effective to lower serum cholesterol levels in hypercholeserolemic rats. Finally, we tested if walnuts consumption would be hypocholesterolemic for Japanese. A diet containing walnuts effectively lowered the serum total and low density lipoprotein cholesterol in Japanese men and women. These animal and human experiments would be relevant to advocate publics to keep consuming diets including soybean, rice and nuts for their healthful life.