AN EXTRACT OF SOY FLOUR INFLUENCES SERUM-CHOLESTEROL AND THYROID-HORMONES IN RATS AND HAMSTERS

The effects of an ethanol-acetone extract from soy flour on serum lipi ds and thyroid hormones were studied in rats and hamsters. In Study 1, male Sprague-Dawley rats were fed diets containing protein from ethan ol-acetone extracted isolated soy protein (ISP-), nonextracted ISP (IS P), casein (casein-), or casein to which 0.36 mg ethanol-acetone extra ct/g protein was added (casein+). Rats fed either ISP-containing diet had lower serum total cholesterol concentrations compared with those f ed either casein diet (P < 0.05). Lower serum LDL-cholesterol concentr ations were present in rats fed either ISP-containing diet and in thos e fed casein+ compared with those fed casein- (P < 0.05). Adding the e xtract to casein (casein+) produced higher serum thyroxine concentrati on and free thyroxine indices compared with all other groups (P < 0.05 ). In Study 2, male Golden Syrian hamsters were fed experimental diets containing protein from ISP, ISP with added ethanol-acetone extract ( 0.36 mg extract/g protein; ISP+), casein-, casein+ (0.36 mg extract/g protein), or casein with twice the level of extract (0.72 mg/g protein ; casein++). Lower serum total cholesterol and LDL (LDL + VLDL + IDL) cholesterol concentrations were observed in hamsters fed ISP, ISP+ or casein+ compared with those fed casein- (P < 0.05). Addition of the ex tract at higher levels to casein (casein+ +) did not lower serum lipid s relative to those fed casein-. Serum thyroxine concentration and the free thyroxine index were greater in both ISP groups as well as in ha msters fed casein++ compared with those fed casein- or casein+ (P < 0. 05). In conclusion, both studies show that protein from soybeans decre ases serum total and LDL cholesterol while the effects on thyroxine ar e different in rats and hamsters. It is also apparent that the ethanol -acetone extract of soy flour produces changes in serum cholesterol, p articularly in the LDL fraction in both species.