An Extract of Soy Flour Influences Serum Cholesterol and Thyroid Hormones in Rats and Hamsters

Abstract

The effects of an ethanol-acetone extract from soy flour on serum lipids and thyroid hormones were studied in rats and hamsters. In Study 1, male Sprague-Dawley rats were fed diets containing protein from ethanol-acetone extracted isolated soy protein (ISP-), nonextracted ISP (ISP), casein (casein-), or casein to which 0.36 mg ethanol-acetone extract/g protein was added (casein+). Rats fed either ISP-containing diet had lower serum total cholesterol concentrations compared with those fed either casein diet (P < 0.05). Lower serum LDL-cholesterol concentrations were present in rats fed either ISP-containing diet and in those fed casein+ compared with those fed casein- (P < 0.05). Adding the extract to casein (casein+) produced higher serum thyroxine concentration 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 extract at higher levels to casein (casein++) did not lower serum lipids relative to those fed casein-. Serum thyroxine concentration and the free thyroxine index were greater in both ISP groups as well as in hamsters fed casein++ compared with those fed casein- or casein+ (P < 0.05). In conclusion, both studies show that protein from soybeans decreases serum total and LDL cholesterol while the effects on thyroxine are different in rats and hamsters. It is also apparent that the ethanol-acetone extract of soy flour produces changes in serum cholesterol, particularly in the LDL fraction in both species.

Isoflavone Glycitein Diminished Plasma Cholesterol in Female Golden Syrian Hamsters

“…The experimental diets contained ∼37% of energy as fat, 25% casein, and 0.1% cholesterol (8). Rice flour was used as a carbohydrate source to prevent "wet tail" disease, a chronic diarrhea that may kill hamsters (1).…”

The Effect of Cost Effective and Useful Diets on Blood Parameters in Female Mice

“…Therefore, consumption of vegetable protein is being increased every day. Soybean is a widely used vegetable seed [8]. In this study, diets containing soybean meal showed a significant decrease in blood cholesterol levels than the control group.…”

“…Methionine and low ratio of lysine to arginine, a parameter that decreases cholesterol, are constituent components of soybean protein [7]. Also some nonprotein compounds of soybean are reported to have beneficial effects on improvement of plasma cholesterol [8]. In addition, soybean contains the highest level of isoflavones among vegetable proteins.…”

Health benefits of soy beans and soy products: a review

“…It is well known that mammalian oestrogens have a significant impact on serum lipids, promoting decreases in LDL and increases in HDL cholesterol. Evidence for an effect of isoflavones on serum cholesterol concentrations has been demonstrated in rats, hamsters, nonhuman primates and humans (Cassidy et al, 1995;Pelletier et al, 1995;Anthony et al, 1996;Balmir et al, 1996;Clarkson et al, 1998). The three primate studies reported by Anthony et al (1994Anthony et al ( , 1995aAnthony et al ( , 1995b demonstrated that soy protein rich in isoflavones favourably affected serum lipids, and that soy protein from which the oestrogens had been extracted had a minimal effect.…”