日本北海道大学微生物生理学横田笃教授领导的一个研究小组发现，食用多的食物会促进更多消化液（胆汁）分泌，进而杀死对人体有益的细菌，对肠内细菌平衡有着破坏作用。消化液分泌还可能引起内脏脂肪综合征和大肠癌的发生。
研究小组在大鼠的普通饵料中添加与食用高脂肪后分泌的浓度相当的胆汁，连续让大鼠食用10天，然后观察大鼠盲肠的细菌变化情况。
一般情况下，大鼠的盲肠中约有1000种细菌，但食用混合胆汁的饵料后，大鼠盲肠内仅梭菌（Clostridium）类细菌就占了98.6%，而正常喂养情况下大鼠盲肠中普遍存在的10%左右的乳酸菌几乎找不到。梭菌在细菌总量中超过半数这一数据，与美国肥胖病人的调查结果具有相似性。
该研究成果发表在美国消化病学会专业期刊《肠胃病学》11月号上。（生物谷 Bioon.com）
doi:10.1053/j.gastro.2011.07.046
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Bile Acid Is a Host Factor That Regulates the Composition of the Cecal Microbiota in Rats
K.B.M. Saiful Islam
Background & Aims Alterations in the gastrointestinal microbiota have been associated with metabolic diseases. However, little is known about host factors that induce changes in gastrointestinal bacterial populations. We investigated the role of bile acids in this process because of their strong antimicrobial activities, specifically the effects of cholic acid administration on the composition of the gut microbiota in a rat model. Methods Rats were fed diets supplemented with different concentrations of cholic acid for 10 days. We used 16S ribosomal RNA gene clone library sequencing and fluorescence in situ hybridization to characterize the composition of the cecal microbiota of the different diet groups. Bile acids in feces, organic acids in cecal contents, and some blood parameters were also analyzed. Results Administration of cholic acid induced phylum-level alterations in the composition of the gut microbiota; Firmicutes predominated at the expense of Bacteroidetes. Cholic acid feeding simplified the composition of the microbiota, with outgrowth of several bacteria in the classes Clostridia and Erysipelotrichi. Externally administered cholic acid was efficiently transformed into deoxycholic acid by a bacterial 7α-dehydroxylation reaction. Serum levels of adiponectin decreased significantly in rats given the cholic acid diet. Conclusions Cholic acid regulates the composition of gut microbiota in rats, inducing similar changes to those induced by high-fat diets. These findings improve our understanding of the relationship between metabolic diseases and the composition of the gastrointestinal microbiota.
