益生菌酸奶对肠道菌群的影响微乎其微

益生菌行径诡异

Probiotic yoghurts have only a small effect on gut bacteria.

益生菌酸奶对肠道菌群的影响微乎其微。

Ed Yong

爱德·杨

Probiotic yoghurts seem to have little effect on the population of bacteria in the human gut.Van Osaka/Photononstop/Glowimages.com

似乎益生菌酸奶对人类肠道菌群数量的影响甚微。凡·奥萨卡/Photononstop/Glowimages.com

Many yoghurts are loaded with live bacteria, and labelled with claims that consuming these microorganisms can be good for your health. But a study published today shows that such yoghurts have only subtle effects on the bacteria already in the gut and do not replace them.

很多酸奶都添加了活性益生菌，并贴上了称该类微生物有益健康的标签。但今日发布的一项研究显示此类酸奶对肠道内已有细菌影响甚微，亦无替代作用。

Nathan McNulty, a microbiologist at Washington University in St Louis, Missouri, recruited seven pairs of identical twins, and asked one in each pair to eat twice-daily servings of a popular yoghurt brand containing five strains of bacteria.

密苏里州华盛顿大学圣路易斯分校的微生物学家内森·迈克那提募用了七对同卵双胞胎，并要求每对中的一人每日饮用两次含有五种不同菌种的主流品牌益生菌酸奶。

By sequencing bacterial DNA in the twins' stool samples, the team showed that the yoghurt microbes neither took up residence in the volunteers' guts, nor affected the make-up of the local bacterial communities.

通过给双胞胎粪便样本中细菌的DNA测序，该（研究）小组证明酸奶中的细菌既不会侵占志愿者的肠道，也不会影响原有菌群的构成。

Jeffrey Gordon, the microbiologist at Washington University who led the study, was not surprised. "We were only giving several billion bacterial cells in total to the twins, who harbour tens of trillions of gut microbes in their intestines," he says.

该研究的带头人--华盛顿大学微生物学家杰弗里·戈登对此并不感到诧异。他说：“我们总共只给了双胞胎们几十亿个细菌细胞，而他们的肠道内寄居了数十万亿肠道细菌”。

Murine model

小鼠模型

McNulty also fed the five bacterial strains from the yoghurt to 'gnotobiotic' mice — animals raised so that the only microorganisms that their guts contain are 15 species found in humans.

麦克那提也向“定菌”鼠饲喂了含这五种细菌的酸奶。定菌鼠，即肠道中只含有人类肠道中已知的15种细菌的小鼠。

As with the twins, the yoghurt bacteria did not change the composition of the rodents' resident communities. However, the activity of genes that allow the native bacteria to break down carbohydrates did increase. One of the five yoghurt strains — Bifidobacterium animalis lactis — also showed a similar boost in its ability to metabolize carbohydrates.

同双胞胎一样，酸奶中的细菌并不能改变该啮齿动物的本身的菌群构成。然而，基因活动使固有细菌的碳水化合物分解量增加。五种酸奶细菌中的耐氧性双歧杆菌的碳水化合物代谢能力也显现出类似增长。

The study, which was funded by the US National Institutes of Health and Danone Research, the research arm of the food company that makes some probiotic yoghurts, was published in Science Translational Medicine1.

这项由美国国立卫生研究所及生产益生菌酸奶的食品公司的分支机构--达能研究中心提供经费的研究发表于首期《科学转化医学》（译者注：杂志名）。

Companies that sell foods with added ingredients that are intended to boost health or prevent illness are under increasing pressure to substantiate the claims about their products. The pressure was increased earlier this year, when the European Food Safety Agency criticized many products, following an extensive three-year review.

出售添加意在促进健康或是防止疾病的原料的食物的公司面临着日益加重的压力--证实他们产品宣传中的功效的压力。今年早些时候，在一个粗放的三年回顾之后欧洲食品安全局抨击了许多产品，这使压力加剧。

The health claims are hard to test, says Gordon, because there is so much variety in the bacteria in the yoghurts and in the people who consume them, but gnotobiotic mouse models will be vital for such studies. Using the mice, he can examine the effect of probiotic foods under tightly controlled conditions, with "defined communities where all the actors and genes are known". The mouse models "provide a foundation for critically evaluating the claims from manufacturers of functional foods and probiotics", he says.

戈登称，这些健康作用很难被证实，因为酸奶中添加的细菌种类繁多，且购买者体内菌种各异，而小鼠模型对此类研究至关重要。老鼠及“所有反应物及基因均已明确的群落”使他得以在严格控制的条件下检测益生菌食品的作用。

More twins needed

需要更多双胞胎

It's too early to be drawing conclusions, say other researchers.

其他研究者称现在就下结论为时尚早。

Dusko Ehrlich, a microbiologist at the French National Institute for Agricultural Research (INRA), thinks that the team did not look at enough twins, or sequence their bacterial genes at enough depth. "We should reserve the judgement on the effects of probiotics in humans until broader and deeper studies are carried out," he says.

法国农业研究院的微生物学家达斯科·厄林奇认为该团队的双胞胎数据不够，或DNA测序深度不够。他说：“我们应该在做出更深更广的研究时再为益生菌对人类的影响下定论。”

Jens Walter, a microbiologist at the University of Nebraska-Lincoln calls the work an "impressive technical achievement". However, he cautions that there are limits to studying mice with human gut bacteria, because different species have their own specifically evolved sets.

内布拉斯加大学林肯分校的微生物学家延斯·沃尔特称该项研究为“瞩目的技术成就”。然而，他提醒到，用老鼠研究人类肠道细菌有局限性，因为不同物种进化出的器官组不尽相同。

McNulty acknowledges the problem. But, he says, "we're always looking to refine these mouse models to be more like the human context. The fact that we see shared responses in mice and humans is good evidence that we're doing something right."

麦克那提承认此问题确实存在。但他说：“我们经常改进这些老鼠模型，使它们更接近人体环境。我们看到的人类与老鼠相同的反应就是我们正在使用正确途径的一个有利证据。”

Gordon now wants to find out exactly how the ingested microbes influence the entrenched ones. "These are very dynamic systems with a lot of cross-talk," he says. "We don't know the nature of the conversation that's occurring."

戈登现在希望找出摄入的微生物对固有微生物产生影响的确切方式。“这些时常相互干扰的机制十分活跃，”他说，“我们不知道它们之间所进行的交流的本质。”