Hara H, Haga S, Kasai T, Kiriyama S
Laboratory of Nutritional Biochemistry, Department of Bioscience and Chemistry, Faculty of Agriculture, Hokkaido University, Sapporo 060, Japan.
J Nutr. 1998 Apr;128(4):688-93. doi: 10.1093/jn/128.4.688.
Plasma cholesterol concentration is reduced by feeding some dietary fibers but the mechanism is not fully understood. We examined whether cecal fermentation products are involved in lowering plasma cholesterol by feeding rats a highly fermentable sugar-beet fiber (SBF) in four separate experiments. These were designed to investigate the effects on plasma cholesterol of oral ingestion of fermentation products on plasma cholesterol, the effects of the products in comparison with that of a short-chain fatty acid (SCFA) mixture, effects of individual SCFA and effects of alteration of energy and nitrogen ratio in the diet by the addition of the SCFA mixture. Cecal contents of rats were cultured with SBF by using a jar fermenter under anaerobic conditions, and the supernatant from the culture medium, containing fermentation products of SBF, was collected and freeze-dried before feeding to rats. Yield of fermentation products as dry weight from the fiber was 80-90%. In rats fed a diet containing fermentation products (80 g/kg diet), plasma cholesterol concentrations were lower than in rats of the fiber-free group 3, 7 and 14 d after feeding the test diet. Major SCFA in the fermentation products were sodium salts of acetic, propionic and butyric acids. Plasma cholesterol concentration in rats fed the diet containing a mixture of equal amounts of the three SCFA salts (66 g/kg diet) as the fermentation products diet was also lower than that in the fiber-free group and was not different from those in rats fed SBF (100 g/kg diet) and the fermentation products. In rats fed an acetate-containing diet but not in rats fed diets without acetate, plasma cholesterol was significantly lower than in the fiber-free group. In conclusion, absorption of SCFA from cecal fermentation products lowers plasma cholesterol. Acetate, and not propionate, may be responsible for lowering plasma cholesterol concentration.
喂食某些膳食纤维可降低血浆胆固醇浓度，但其机制尚未完全明确。我们通过在四项独立实验中给大鼠喂食高度可发酵的甜菜纤维（SBF），研究盲肠发酵产物是否参与降低血浆胆固醇。这些实验旨在研究口服发酵产物对血浆胆固醇的影响、与短链脂肪酸（SCFA）混合物相比产物的影响、单一SCFA的影响以及通过添加SCFA混合物改变饮食中能量和氮比例的影响。在厌氧条件下，使用广口瓶发酵罐将大鼠盲肠内容物与SBF一起培养，收集培养基上清液（含有SBF的发酵产物），冻干后喂给大鼠。纤维发酵产物的干重产量为80 - 90%。在喂食含发酵产物饮食（80 g/kg饮食）的大鼠中，喂食试验饮食后3、7和14天，其血浆胆固醇浓度低于无纤维组大鼠。发酵产物中的主要SCFA是乙酸、丙酸和丁酸的钠盐。喂食含有等量三种SCFA盐混合物（66 g/kg饮食）作为发酵产物饮食的大鼠，其血浆胆固醇浓度也低于无纤维组，且与喂食SBF（100 g/kg饮食）和发酵产物的大鼠无差异。在喂食含乙酸饮食的大鼠中，血浆胆固醇显著低于无纤维组，但在不含有乙酸饮食的大鼠中则不然。总之，盲肠发酵产物中SCFA的吸收可降低血浆胆固醇。乙酸而非丙酸可能是降低血浆胆固醇浓度的原因。
