J Nutri：抗性淀粉有助于预防肠癌

澳大利亚联邦科工组织CSIRO的科学家最新发现，摄入抗性淀粉有益于肠道健康，并能预防诱发肠癌的基因损伤。相关研究成果刊登在了近日的国际杂志The Journal of Nutrition上。
    
    肠癌是世界上最常见的恶性肿瘤之一。以往的科学研究认为，饮食结构中纤维摄入量较少是西方人肠癌发病率较高的原因。然而与之相悖的是，尽管澳大利亚人平均每天摄入的纤维数量高过其他西方国家，肠癌仍然在澳大利亚所有肿瘤发病率中排名第二，平均每天新增三十位澳大利亚人被发现患有肠癌。
   
    澳大利亚联邦科工组织CSIRO的David Topping博士称以上现象为“澳大利亚悖论”。在未来食物旗舰计划（Food Futures Flagship）的支持下，联邦科工组织的科学家们发现，这一悖论的答案在于澳大利亚人没有摄入足够的抗性淀粉。Topping博士介绍，人体摄入纤维的数量固然重要，但纤维的多样性则更重要;膳食纤维有益于人体健康，而抗性淀粉对人体则更为有益。
   
    同时，在联邦科工组织CSIRO健康预防旗舰计划（Preventative Health Flagship）的支持下，大肠癌研究专家Trevor Lockett博士发现，在饮食中增加抗性淀粉的量可以减少肠癌发病率。
   
    研究结果显示，抗性淀粉的摄入量应该是每天20克左右，相当于每天吃3杯煮熟的扁豆，这比典型的西方饮食习惯中抗性淀粉的摄入量多出近四倍。

    专家们认识到，目前从澳大利亚人习惯的饮食结构中很难满足每天20克抗性淀粉的摄入量，因此，他们正在培育抗性淀粉含量较高的小麦等经常食用的谷物品种，然后，通过加工谷物制作面包等食品，使澳大利亚人更容易地从饮食获得足够的抗性淀粉。

doi:10.3945/​jn.111.147660
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Resistant Starches Protect against Colonic DNA Damage and Alter Microbiota and Gene Expression in Rats Fed a Western Diet

Michael A. Conlon4–6, Caroline A. Kerr4,7, Christopher S. McSweeney4,8, Robert A. Dunne4,9, Janet M. Shaw4,7, Seungha Kang4,8, Anthony R. Bird4–6, Matthew K. Morell5,10, Trevor J. Lockett4,7, Peter L. Molloy4,7, Ahmed Regina5,10, Shusuke Toden4–6, Julie M. Clarke4,6, and David L. Topping4–6*

Resistant starch (RS), fed as high amylose maize starch (HAMS) or butyrylated HAMS (HAMSB), opposes dietary protein-induced colonocyte DNA damage in rats. In this study, rats were fed Western-type diets moderate in fat (19%) and protein (20%) containing digestible starches [low amylose maize starch (LAMS) or low amylose whole wheat (LAW)] or RS [HAMS, HAMSB, or a whole high amylose wheat (HAW) generated by RNA interference] for 11 wk (n = 10/group). A control diet included 7% fat, 13% protein, and LAMS. Colonocyte DNA single-strand breaks (SSB) were significantly higher (by 70%) in rats fed the Western diet containing LAMS relative to controls. Dietary HAW, HAMS, and HAMSB opposed this effect while raising digesta levels of SCFA and lowering ammonia and phenol levels. SSB correlated inversely with total large bowel SCFA, including colonic butyrate concentration (R2 = 0.40; P = 0.009), and positively with colonic ammonia concentration (R2 = 0.40; P = 0.014). Analysis of gut microbiota populations using a phylogenetic microarray revealed profiles that fell into 3 distinct groups: control and LAMS; HAMS and HAMSB; and LAW and HAW. The expression of colonic genes associated with the maintenance of genomic integrity (notably Mdm2, Top1, Msh3, Ung, Rere, Cebpa, Gmnn, and Parg) was altered and varied with RS source. HAW is as effective as HAMS and HAMSB in opposing diet-induced colonic DNA damage in rats, but their effects on the large bowel microbiota and colonocyte gene expression differ, possibly due to the presence of other fiber components in HAW.