Effects of Soy Protein Isoflavones on Serum Lipids, Lipoprotein Profile and Serum Glucose of Hypercholesterolemic Rabbits

The main objective of this research was to determine the effects of soy protein isoflavones on serum lipids, lipoproteins and fasting blood sugar levels in hypercholesterolemic rabbits_ Materials and Method: Twenty-four male New Zealand rabbits received the basic pellet diet for two weeks and were then placed on a hypercholesterolemic diet (pellets plus 1% cholesterol) for three weeks. Mter elevation of total cholesterol, the rabbits were randomly allocated into four experimental groups. Groups 1 to 3 received loog soy protein containing 200mg (SPI+), lOOmg (SPI50%) soy protein diet and without isoflavones (SPI-), respectively, for six weeks. The fourth group was kept on the hypercholesterolemic diet (HC).
Results: Findings showed that cholesterol rich diet produced significant increase in total, LDLand HDL-cholesterol concentrations. In SPI+ group these parameters remained unchanged, compared with SPI-and SPI50% groups (P<0.000l). HDL-cholesterol was significantly elevated after administration of HC diet and remained high (almost three fold) in all soy diets relative to baseline. However, its level was significantly lower in SPI50% compared with SPIgroup (p<0.0l). Triglycerides and VLDL concentrations were significantly increased in SPI50% compared with baseline and HC groups (P<0.03). Fasting blood sugar levels were not changed in all soy treatment groups. Conclusions: These results suggest that intact soy protein isoflavones ameliorate the lipid profile in spite of high-cholesterol intake, but has no obvious effect on blood sugar levels and can therefore be useful in hyperlipidemias especially when cholesterol intake is simultaneously decreased. Moreover, there is no direct doseresponse relationship between soy isoflavone content and its lipid-lowering effect.