Prevention of hypercholesterolemia and atherosclerosis in Japanese quail by high intake of soy protein.

This study was undertaken to determine the influence of levels of soy protein on cholesterol metabolism and the development of atherosclerosis in Japanese quail (Coturnix coturnix japonica). Quail were fed purified diets containing one of four levels (10, 20, 40 or 60%) of soy protein either with (atherogenic) or without (control) 0.5% cholesterol. Results showed that higher proportions of protein (40 and 60%) in atherogenic diets had a preventive effect on the development of atherosclerosis in adult male quail. For the atherogenic diets the higher protein levels resulted in significantly lower serum and aorta cholesterol concentrations than observed with the 10 or 20% protein levels and free of aortic atherosclerosis. A dual isotope technique was used to measure the absorption rates for cholesterol in quail fed with 20 and 40% soy protein. Absorption rates were not affected by the level of dietary protein but were influenced by the presence of dietary cholesterol. Relative rates were 40% in quail fed control diets and 30% in quail fed atherogenic diets. The excretion of neutral sterols, largely cholesterol, and bile acids increased with the high intake of soy protein. These results demonstrate that in quail the presence of higher dietary levels of soy protein has both a hypocholesterolemic action and a preventive effect on cholesterol-induced atherosclerosis and one of the possible mechanisms is through increased excretion of cholesterol.