In the intestines and in the feces of 7-month-old germ-free and conventional male mice, Sulfated and non-sulfated bile acids are determined. The major bile acids from germ-free mice are cholic acid, α-Muricholic acid and β-Muricholic acid. Compared with the high-fat diet control group, in high-fat diet (HFD)-soy protein isolate (SPI) mice, in the case of primary bile acids, alpha-murline acid was greatly reduced.