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目的观察大豆蛋白对人体血浆胆固醇浓度的影响并探讨其作用机制。方法选择健康大学生30名,男女各半,平均年龄为20.7±1.1岁,按血浆总胆固醇浓度、体重和性别均衡的原则分为3组,每组10人。在统一食谱集中就餐的基础上,分别另外摄入酪蛋白粉(含30g蛋白质)、大豆分离蛋白粉(含30g蛋白质)或酪蛋白粉(含30g蛋白质)加碳酸钙粉(含880mgCa),共14d。实验开始和结束时。测量身高、体重,计算体质指数(BMI);采血,测定血浆总胆固醇(TC)、总甘油三酯(TG)、低密度脂蛋白胆固醇(LDL-C)、高密度脂蛋白胆固醇(HDL-C)、载脂蛋白AI(Apo-AI)和载脂蛋白B(Apo-B)的浓度。实验结束前,收集3d粪便,测定粪脂肪、钙、磷、镁和胆汁酸的排出量。结果 1.同实验开始时相比,酪蛋白粉可明显升高血浆TC,上升幅度为11%(P<0.01),而大豆分离蛋白粉仅为6%(P>0.05),碳酸钙升高血浆TC的作用最小,为2.3%(P>0.05)。2.3d代谢实验结果表明,同酪蛋白组相比,大豆蛋白组的粪钙、磷和镁的排出量显著增加,分别增加了60.3%(P<0.05)、44.1%(P<0.05)和55.0%(P<0.01);粪脂肪和胆汁酸排出量趋于增加,分别增加了33.6%和45.3%。而酪蛋白加钙组的粪磷和胆汁酸排出量略高于酪蛋白组,粪镁和脂肪的排出量略低于酪蛋白组,但差异无显著性。3.相关分析结果表明,随粪钙、磷、镁和脂肪的排出量增加,粪胆汁酸排出量也明显增加。呈显著正相关。血浆TC随粪胆汁酸排出量增加呈下降的趋势。结论摄入酪蛋白粉明显升高人体血浆胆固醇浓度,而大豆分离蛋白粉或增加钙摄入的作用不明显; 同酪蛋白相比,大豆蛋白明显增加人体粪钙、磷、镁的排出量,粪胆汁酸排出量趋于增加:增加钙摄入的结果与摄入大豆蛋白相似。这些结果都支持大豆蛋白降血胆固醇的可能机制是由于增加了粪胆汁酸的排出量而导致肝脏中由胆固醇合成胆汁酸的增加,最终降低了血浆TC浓度。本实验仅从物质代谢的角度探讨了大豆蛋白降低血胆固醇的作用机制,但要彻底阐明这一机制,还需进一步在大豆植物化学和分子生物学方面做大量深入细致的研究工作。
Objective To observe the effect of soybean protein on human plasma cholesterol concentration and to explore its mechanism. Methods 30 healthy college students, male and female, with an average age of 20.7 ± 1.1 years, were divided into 3 groups according to the total plasma cholesterol, body weight and gender balance. On the basis of a unified diet, respectively, casein powder (containing 30g protein), soy protein isolate (containing 30g protein) or casein protein (containing 30g protein) plus calcium carbonate powder (containing 880mgCa) 14d. The experiment begins and ends. Body height and weight were measured to calculate body mass index (BMI). Blood samples were taken for determination of plasma TC, TG, LDL-C, ), Apolipoprotein AI (Apo-AI), and apolipoprotein B (Apo-B). Before the end of the experiment, 3d manure was collected and measured for fecal fat, calcium, phosphorus, magnesium and bile acid excretion. Results 1. Compared with the beginning of the experiment, casein powder significantly increased plasma TC by 11% (P <0.01), while only 6% (P> 0.05) soy protein isolate and calcium carbonate increased The effect of plasma TC was minimal at 2.3% (P> 0.05). 2.3d Metabolism experiments showed that compared with the casein group, the excretion of calcium, phosphorus and magnesium in soybean protein group increased significantly by 60.3% (P <0.05), 44.1% (P <0.05) and 55.0 % (P <0.01). Excretion of fecal fat and bile acid tended to increase by 33.6% and 45.3% respectively. In the casein plus calcium group, the excretion of fecal phosphorus and bile acid was slightly higher than that of the casein group. The excretion of feces magnesium and fat was slightly lower than that of the casein group, but the difference was insignificant. Correlation analysis showed that manure bile acid excretion increased significantly with the increase of calcium, phosphorus, magnesium and fat excretion. There was a significant positive correlation. Plasma TC decreased with increasing bile acid excretion. Conclusions Ingestion of casein powder significantly increased the plasma cholesterol concentration in the human body, whereas soy protein isolate or increased calcium intake had no obvious effect. Compared with casein, soy protein significantly increased the excretion of calcium, phosphorus and magnesium in human body, Fecal bile acid excretion tends to increase: Increasing calcium intake is similar to ingesting soy protein. These results all support the possible mechanism of the hypocholesterolemia of soy protein by increasing the cholesterol bile acid excretion in the liver by increasing the excretion of fecal bile acid and eventually lowering the plasma TC concentration. This experiment explored the mechanism of soybean protein lowering blood cholesterol only from the perspective of material metabolism. However, thorough elucidation of this mechanism needs a lot of in-depth and meticulous research in soybean phytochemistry and molecular biology.