The effect of fermented soymilk on rats fed a high cholesterol diet was investigated to clarify the cholesterol-lowering function. Male Sprague-Dawley rats aged 7 weeks were fed a control diet (1% cholesterol, high cholesterol diet), high cholesterol diet containing 11.7% fermented soymilk diet (5% soy protein as final concentration, F-5), or high cholesterol diet containing 23.4% fermented soymilk diet (10% soy protein as final concentration, F-10) for 5 weeks. The liver weight and fat mass were decreased by the ingestion of fermented soymilk. The hepatic triglyceride and cholesterol levels in the F-5 and F-10 groups were significantly lowered compared to those in the control group. The plasma total cholesterol level of the F-10 group was significantly decreased. The expression of SREBP-2, a cholesterol synthesis-related gene, was significantly decreased in liver of the F-5 group, but the expression of CYP7a1, a cholesterol catabolism-related gene, was significantly increased. These results suggest that fermented soymilk can modulate the cholesterol metabolism in rats fed a high cholesterol diet.
Soy foods are known to be effective for the amelioration of lipid metabolism. We investigated the effect of fermented soymilk on lipid metabolism in rats fed a high fat diet. Male Sprague-Dawley rats aged 7 weeks were fed either a control diet (AIN-93G), high fat diet including 28.5 % powdered beef tallow (60 % fat energy), or test diet where 24.1 % of the high fat diet was replaced with fermented soymilk (10 % soy protein in diet) for 5 weeks. Although it was previously reported that the plasma triglyceride level in rats fed a normal diet (AIN-93G) was not decreased by the ingestion of fermented soymilk, it was found in the present study that the level of rats fed a high fat diet containing fermented soymilk was significantly suppressed compared with those of rats fed a high fat diet. Although the hepatic cholesterol level in rats fed a high fat diet was reduced by the ingestion of fermented soymilk, a significant decrease in plasma total cholesterol level, to the level in rats fed a normal diet, was not observed. These lipid metabolism-modulation effects in rats fed a high fat diet seem to depend on the physiological action of fermented soymilk supplemented to the diet.
We investigated the effect of lactic fermented soymilk in improving hepatic lipid metabolism in rats fed a high fat and high cholesterol diet. Male Sprague-Dawley rats, aged 7 weeks, were fed a very high lipid diet (VC diet) or moderately high lipid diet (MC diet) for 5 weeks. The VC diet contained 30 % triacylglycerol (TG) and 0. 5 % cholesterol ; for VF diet (very high lipid diet with fermented soymilk), 25.0 % of the VC diet was replaced with fermented soymilk. The MC diet contained 15 % TG and 0.125 % cholesterol ; for MF diet (moderately high lipid diet with fermented soymilk), 22.2 % of the MC diet was replaced with fermented soymilk. Only hepatic crude lipid and cholesterol contents were significantly suppressed in the VF group, whereas plasma total cholesterol (TC) and TG levels, as well as hepatic crude lipid, cholesterol and TG contents were significantly suppressed in the MF group. There was no down-regulation of hepatic lipid metabolism-related gene expression in the VF group ; in contrast, the expression of FAS was down-regulated in the MF group. These results suggested that the effect of fermented soymilk in improving lipid metabolism was small in rats fed the VC diet, likely due to reduced hepatic metabolic function caused by lipid overloading, whereas ingestion of fermented soymilk effectively suppressed the accumulation of hepatic lipid and the elevation of plasma lipid levels in rats fed a MC diet. Keywords : lactic fermented soymilk, lipid metabolism, high fat and high cholesterol diet, rat, modulation of hepatic gene expression, fatty liver キーワード : 乳酸発酵豆乳,脂質代謝改善作用,高脂肪高コレステロール食,ラット,肝臓遺伝子発現調節 先進国を初めとする世界各国で肥満が増加傾向にあり, メタボリックシンドロームによる動脈硬化や糖尿病などの リスク増加が懸念されている 1) .また,メタボリックシンド ロームで見られる脂肪肝では肝臓の代謝機能低下を生じて いる 2) .食品機能成分には肝臓脂質蓄積および脂肪肝の防 止作用を示すものがあり,肝臓脂質蓄積抑制に大豆タンパ ク質の脂質代謝改善作用が有効であることはよく知られて いる 3) 4) .また,大豆タンパク質のように強い生理作用はな いが,大豆イソフラボンも肝臓脂質代謝改善に作用すると 報告されている 5) 6) .最近,大豆発酵食品による脂質代謝改 善効果について報告があり 7) 8) ,著者らの研究室でも豆乳の 乳酸発酵物の脂質代謝改善作用に注目し,ラットへの乳酸 発酵豆乳投与によって肝臓脂質代謝改善作用を示すことを 明らかにした 9) .また,高脂肪食を投与したラットに乳酸発 酵豆乳を摂取させると血漿トリアシルグリセロール(以下 TG)低下作用,肝臓コレステロール低下作用が認められ
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