Richardson Centre for Functional Foods and Nutraceuticals, University of Manitoba, 196 Innovation Drive, Winnipeg, MB R3T 6C5, Manitoba, Canada.
J Clin Lipidol. 2008 Apr;2(2):S4-S10. doi: 10.1016/j.jacl.2008.01.005.
Several food components have been demonstrated to exhibit cholesterol-lowering properties by interfering with cholesterol absorption and bile-acid trafficking. Such components include stearic acid, plant sterols, soluble fiber, and soy protein. Among saturated fatty acids, stearic acid is unique in its ability to reduce circulatory low-density lipoprotein cholesterol levels. This action is accompanied by an observed suppression in cholesterol absorption, an effect seen repeatedly in animal and human studies. Proposed mechanisms include micellar exclusion of cholesterol by this high melting point fatty acid, as well as the ability of stearate to alter the biliary ratios of primary to secondary bile acids, leading to a reduction in hydrophobicity index and lower overall solubility of sterols in micelles. Another dietary ingredient that interferes with absorption of sterols is soy protein, in which studies in animals and humans have identified that compared to casein, consumption of soy protein reduces intestinal absorption of cholesterol while enhancing fecal cholesterol excretion. Considerable investigation using free amino acid mixtures mirroring the composition of soy versus animal proteins has determined that co-existing agents other than soy's amino acid pattern are likely responsible for the inhibitory action of soy protein on sterol uptake. Recently, it has been shown that hydrolysates of soy protein appear to be effective in reducing sterol absorption; these are now being targeted as the possible factor responsible for the overall effect of this dietary ingredient. Plant sterols appear to impact absorption of sterols through several mechanisms, including competition with cholesterol for incorporation into micelles, co-crystallization with cholesterol to form insoluble crystals, interaction with digestive enzymes, and inhibition of cholesterol transporter proteins. Clinical trials attest to plant sterols lowering cholesterol absorption by 20% to 40%, an extent beyond which cholesterogenesis can compensate to restore normal circulatory cholesterol levels. As such, 2 g/day of plant sterols effectively lowers low-density lipoprotein cholesterol by 8% to 12%. Dietary soluble fiber represents another means of reducing intestinal cholesterol uptake, in part through enhanced bile-acid clearance through the gut. Pectin, β-glucans, fructans, and gums have been identified as agents that can work through the production of a viscous matrix that hinders movement of cholesterol and bile acids into micelles as well as the subsequent uptake of micelles into the enterocyte. Additional work on design of novel fibers that impede sterol absorption is warranted. In summary, a number of novel dietary factors exist that contribute to heart disease risk reduction via mechanisms that involve cholesterol absorption inhibition and/or biliary pathway perturbation.
几种食物成分已被证明通过干扰胆固醇吸收和胆汁酸转运具有降低胆固醇的特性。这些成分包括硬脂酸、植物固醇、可溶性纤维和大豆蛋白。在饱和脂肪酸中，硬脂酸是唯一能够降低循环低密度脂蛋白胆固醇水平的脂肪酸。这种作用伴随着胆固醇吸收的观察到的抑制，这种作用在动物和人体研究中反复出现。提出的机制包括这种高熔点脂肪酸通过胶束排除胆固醇，以及硬脂酸盐改变初级胆汁酸与次级胆汁酸的胆汁比例，导致疏水性指数降低和胆固醇在胶束中的整体溶解度降低。另一种干扰固醇吸收的饮食成分是大豆蛋白，动物和人体研究表明，与酪蛋白相比，食用大豆蛋白可降低胆固醇在肠道中的吸收，同时增加粪便中胆固醇的排泄。使用与大豆和动物蛋白组成相似的游离氨基酸混合物进行了大量研究，确定除了大豆的氨基酸模式之外，共同存在的其他物质可能是大豆蛋白抑制固醇摄取的原因。最近，已经表明大豆蛋白的水解产物似乎可有效降低固醇吸收；这些现在被作为负责这种饮食成分整体作用的可能因素。植物固醇似乎通过几种机制影响固醇的吸收，包括与胆固醇竞争掺入胶束、与胆固醇共结晶形成不溶性晶体、与消化酶相互作用以及抑制胆固醇转运蛋白。临床试验证明植物固醇可降低胆固醇吸收 20%至 40%，超过了胆固醇生成可以补偿以恢复正常循环胆固醇水平的程度。因此，每天 2 克植物固醇可有效降低低密度脂蛋白胆固醇 8%至 12%。膳食纤维是另一种减少肠道胆固醇吸收的方法，部分原因是通过肠道增强胆汁酸清除。果胶、β-葡聚糖、果聚糖和树胶已被确定为可通过产生粘性基质来发挥作用的物质，该基质阻碍胆固醇和胆汁酸进入胶束以及随后胶束进入肠细胞。有必要进一步研究设计可阻碍固醇吸收的新型纤维。总之，存在几种新型饮食因素，通过涉及胆固醇吸收抑制和/或胆汁途径扰动的机制有助于降低心脏病风险。
