欢迎来到肠道小宇宙：你身体里的"隐形小伙伴"

小时候你有没有过肚子疼的经历？妈妈或者奶奶会摸着你的头说：“是不是肚子里有虫呀？快吃点打虫药。”那时候你可能还会想象肚子里真的有几条白白胖胖的小虫子，在肚子里爬来爬去，闹得你肚子疼。不过等你长大一点就会发现，大部分时候肚子疼并不是真的有虫，而是你身体里那些看不见的“隐形小伙伴”闹脾气啦——它们就是住在你肠道里的微生物，也是我们这本书要讲的“肠道小宇宙”的原住民。

> English Version > When you were little, have you ever had a stomachache? Your mom or grandma might have touched your head and said, "Do you have worms in your tummy? Take some worm medicine." At that time, you might have imagined there were really some fat white worms crawling around in your stomach, making it hurt. But when you grow up a little, you will find that most stomachaches are not caused by real worms, but by the temper of those invisible "little partners" in your body — they are the microorganisms living in your intestines, and also the native residents of the "gut universe" we are going to talk about in this book.

我们把所有住在你肠道里的微生物（包括细菌、真菌、病毒、古菌等等）的总和，叫做“肠道微生物组”（Gut Microbiome）。你别看它们个头小，本事可不小：你吃进去的东西，有很大一部分是它们帮你消化的；你身体需要的某些维生素，是它们帮你合成的；甚至你的情绪好不好，免疫力强不强，都和它们有关系哦。

> English Version > We call the sum of all microorganisms (including bacteria, fungi, viruses, archaea, etc.) living in your intestines the "Gut Microbiome". Although they are small, they have great abilities: a large part of the food you eat is digested by them; some vitamins your body needs are synthesized by them; even your mood and immunity are related to them.

---

一、肠道小宇宙的“居民”长什么样？

肠道微生物里数量最多的是细菌，它们个头非常小，大部分只有$0.5-5\mu m$（微米）长，$1\mu m = 10^{-6}m$，也就是一根头发丝直径的七十分之一左右，你用普通的光学显微镜才能看到它们。你身体里的细菌总数大概有$3.8\times10^{13}$个，也就是38万亿个，比你自己的体细胞总数（大概30万亿个）还要多，相当于你每1个自己的细胞，旁边都跟着1个多细菌小伙伴。

> English Version > The most numerous microorganisms in the gut are bacteria. They are very small, most of them are only $0.5-5\mu m$ long. $1\mu m = 10^{-6}m$, which is one-seventieth of the diameter of a hair. You can only see them with an ordinary optical microscope. The total number of bacteria in your body is about $3.8\times10^{13}$, which is 38 trillion, even more than the total number of your own somatic cells (about 30 trillion). It is equivalent to that every 1 of your own cells is accompanied by more than 1 bacterial partner.

除了细菌，肠道里还有少量的真菌，比如酵母菌、念珠菌，它们大部分时候是“好居民”，只有当你免疫力特别差的时候，才会“闹事”变成致病菌。还有病毒，也就是“噬菌体”，它们专门吃细菌，相当于肠道里的“细菌警察”，负责控制细菌的数量，不让某一种细菌长得太多。还有一类叫“古菌”的微生物，它们和细菌长得有点像，但是遗传物质和细菌不一样，大部分古菌都住在肠道里，帮你分解那些细菌分解不了的食物残渣，还能产生甲烷，不过你不用怕，它们产生的甲烷大部分会被你当成屁放出去哦。

> 💡 小知识：你每天放的屁里，大概有30%的气体是肠道微生物帮你分解食物产生的，比如氢气、甲烷、二氧化碳，这些都是微生物的“代谢产物”哦。 > > 💡 Fun Fact: About 30% of the gas you fart every day is produced by gut microorganisms helping you decompose food, such as hydrogen, methane, and carbon dioxide. These are all "metabolites" of microorganisms.

> English Version > In addition to bacteria, there are also a small amount of fungi in the gut, such as yeast and candida. Most of the time they are "good residents", and they only "make trouble" and become pathogenic bacteria when your immunity is particularly weak. There are also viruses, called "phages", which specialize in eating bacteria. They are equivalent to "bacterial police" in the gut, responsible for controlling the number of bacteria and preventing any kind of bacteria from growing too much. There is also a kind of microorganism called "archaea". They look a bit like bacteria, but their genetic material is different from bacteria. Most archaea live in the gut, helping you decompose food residues that bacteria cannot decompose, and can also produce methane. But don't be afraid, most of the methane they produce will be released as farts.

其实微生物不只住在你的肠道里，你的口腔、皮肤、鼻腔、阴道里都有，不过肠道是它们最大的“聚居地”，全身大概80%的微生物都住在肠道里，尤其是大肠，那里温暖、潮湿、有吃不完的食物残渣，是微生物最喜欢的“

小时候你有没有过肚子疼的经历？妈妈或者奶奶会摸着你的头说：“是不是肚子里有虫呀？快吃点打虫药。”那时候你可能还会想象肚子里真的有几条白白胖胖的小虫子，在肚子里爬来爬去，闹得你肚子疼。不过等你长大一点就会发现，大部分时候肚子疼并不是真的有虫，而是你身体里那些看不见的“隐形小伙伴”闹脾气啦——它们就是住在你肠道里的微生物，也是我们这本书要讲的“肠道小宇宙”的原住民。

> English Version > When you were little, have you ever had a stomachache? Your mom or grandma might have touched your head and said, "Do you have worms in your tummy? Take some worm medicine." At that time, you might have imagined there were really some fat white worms crawling around in your stomach, making it hurt. But when you grow up a little, you will find that most stomachaches are not caused by real worms, but by the temper of those invisible "little partners" in your body — they are the microorganisms living in your intestines, and also the native residents of the "gut universe" we are going to talk about in this book.

我们把所有住在你肠道里的微生物（包括细菌、真菌、病毒、古菌等等）的总和，叫做“肠道微生物组”（Gut Microbiome）。你别看它们个头小，本事可不小：你吃进去的东西，有很大一部分是它们帮你消化的；你身体需要的某些维生素，是它们帮你合成的；甚至你的情绪好不好，免疫力强不强，都和它们有关系哦。

> English Version > We call the sum of all microorganisms (including bacteria, fungi, viruses, archaea, etc.) living in your intestines the "Gut Microbiome". Although they are small, they have great abilities: a large part of the food you eat is digested by them; some vitamins your body needs are synthesized by them; even your mood and immunity are related to them.

---

一、肠道小宇宙的“居民”长什么样？

肠道微生物里数量最多的是细菌，它们个头非常小，大部分只有$0.5-5\mu m$（微米）长，$1\mu m = 10^{-6}m$，也就是一根头发丝直径的七十分之一左右，你用普通的光学显微镜才能看到它们。你身体里的细菌总数大概有$3.8\times10^{13}$个，也就是38万亿个，比你自己的体细胞总数（大概30万亿个）还要多，相当于你每1个自己的细胞，旁边都跟着1个多细菌小伙伴。如果你把肚子里所有的肠道微生物放在一起称重，大概有1-2公斤，和你的一颗大脑袋差不多重哦！

> English Version > The most numerous microorganisms in the gut are bacteria. They are very small, most of them are only $0.5-5\mu m$ long. $1\mu m = 10^{-6}m$, which is one-seventieth of the diameter of a hair. You can only see them with an ordinary optical microscope. The total number of bacteria in your body is about $3.8\times10^{13}$, which is 38 trillion, even more than the total number of your own somatic cells (about 30 trillion). It is equivalent to that every 1 of your own cells is accompanied by more than 1 bacterial partner. If you weigh all the gut microorganisms in your belly together, it will be about 1-2 kg, which is almost the same weight as your big head!

我们用数学公式可以算出细菌和人体细胞的数量比： $$\frac{3.8\times10^{13}}{3.0\times10^{13}} \approx 1.27$$ 也就是说，平均每1个属于你的细胞，旁边就跟着1.27个细菌小伙伴，你其实从来不是“一个人”，而是一个带着几十万亿微生物的“超级生物体”哦！

除了细菌，肠道里还有少量的真菌，比如酵母菌、念珠菌，它们大部分时候是“好居民”，只有当你免疫力特别差、或者吃了太多甜食的时候，才会“闹事”变成致病菌。还有病毒，也就是“噬菌体”，它们专门吃细菌，相当于肠道里的“细菌警察”，负责控制细菌的数量，不让某一种细菌长得太多，避免某一种细菌“霸占”整个肠道。还有一类叫“古菌”的微生物，它们和细菌长得有点像，但是遗传物质和细菌不一样，大部分古菌都住在肠道里，帮你分解那些细菌分解不了的食物残渣，还能产生甲烷，不过你不用怕，它们产生的甲烷大部分会被你当成屁放出去哦。

> 💡 小知识：你每天放的屁里，大概有30%的气体是肠道微生物帮你分解食物产生的，比如氢气、甲烷、二氧化碳，这些都是微生物的“代谢产物”（也就是微生物干活之后产生的“副产品”）。如果你吃了很多洋葱、大蒜或者红薯，屁就会更臭，那是因为这些食物里的特殊成分被细菌分解之后，产生了硫化氢等有臭味的气体哦。 > > 💡 Fun Fact: About 30% of the gas you fart every day is produced by gut microorganisms helping you decompose food, such as hydrogen, methane, and carbon dioxide. These are all "metabolites" (by-products of microorganisms' work). If you eat a lot of onions, garlic or sweet potatoes, your farts will smell worse, because the special ingredients in these foods are decomposed by bacteria to produce smelly gases such as hydrogen sulfide.

> English Version > In addition to bacteria, there are also a small amount of fungi in the gut, such as yeast and candida. Most of the time they are "good residents", and they only "make trouble" and become pathogenic bacteria when your immunity is particularly weak or you eat too much sweet food. There are also viruses, called "phages", which specialize in eating bacteria. They are equivalent to "bacterial police" in the gut, responsible for controlling the number of bacteria and preventing any kind of bacteria from growing too much, to avoid any kind of bacteria "occupying" the whole gut. There is also a kind of microorganism called "archaea". They look a bit like bacteria, but their genetic material is different from bacteria. Most archaea live in the gut, helping you decompose food residues that bacteria cannot decompose, and can also produce methane. But don't be afraid, most of the methane they produce will be released as farts.

其实微生物不只住在你的肠道里，你的口腔、皮肤、鼻腔、阴道里都有，不过肠道是它们最大的“聚居地”，全身大概80%的微生物都住在肠道里，尤其是大肠，那里温暖（刚好是你身体的体温37℃）、潮湿、有吃不完的食物残渣，是微生物最喜欢的“安乐窝”。科学家做过统计，1克人类粪便里就有1