How does food turn into poop?
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This is But Why, a podcast for curious kids from Vermont Public. I'm Jane Lindholm. On this show, we take questions from curious kids just like you, and we find answers. Here at But Why, we don't mind talking about things that might make some adults, and maybe some of you, feel a little squeamish. So today's episode is about something you're probably not supposed to talk about at school or the dinner table or in polite company.

but it's okay to talk about it here on Boat Why. Maybe just don't blast this episode on speaker unless you've warned your adults. We're going to talk about pooping and farting today. We all do it, but there's a lot you probably don't know about how your body processes waste, why it often smells, and other questions you might sometimes be afraid to ask. So today we're going to talk with someone who has written a lot about how and why we poop and fart.

But before we get into all of your questions, I know some of you are probably already dying to make your best fart noise. There are lots of methods. I mean, you can just use your mouth like this. You can use your mouth and your hands. Or your hands and your armpits. I'm not very good at that one.

So let's just get this over with so we don't have it hanging over our heads all episode. Go ahead and let it rip. Make your best fart sound. You've got five seconds. Three, two, one. Okay, that's enough. No more fart sounds. At least no more fart sounds until you've listened to the whole episode. Deal? Let's get to know our guest for today. Her name is Mary Roach.

I'm a writer, but I write books that require a lot of research. But all that means is I go around and I sit down with people who know a lot and I pick their brains and I ask a lot of questions, whatever questions pop into my head. And I have a tape recorder so I can remember what they've said. And then I take all that information and put it in a book. Mary Roach has written eight books, and one of them is of particular interest to our topic.

It's called Gulp! Adventures on the Alimentary Canal. That was the point at which I became something of a weirdo expert on the things that happen between your mouth and your butt. Between your mouth and your butt is a pretty crude description of the Alimentary Canal, but also pretty accurate. The Alimentary Canal, A-L-I-M-E-N-T-A-R-Y, is the passage food takes all the way through your body.

And Mary has written about all of it, including the part at the end. I'm Mateo. I'm eight years old. And I'm wondering, how does your food turn into your poop? I'm Solomon, and I'm six. And I live in St. Paul.

How does food turn into poop? Well, there's several stops along the way, but first thing you have to do is chew it up. So it's kind of a mushy thing that you can swallow and then you form it into a swallowable thing called a bolus. And that slides down the tube into your stomach. And in your stomach, you have this stuff that

kind of begins to break it down into a mushy kind of porridge. And then when it's like a liquidy, porridge-y state, then it gets spurted into your small intestine. And that's where your body is like, oh, food, this looks good. I always thought your stomach was where food got broken down and turned into nutrients. But it turns out I was only half right.

The saliva in your mouth and the stomach acid and other liquids in your stomach do break down your food into smaller and smaller molecules. But most of the nutrients you get from your food are absorbed into your body in the small intestine. There's stuff that your body needs in your small intestine, which is the first part of your intestine. So your body's absorbing, it's taking stuff out of there, like nutrients and proteins and things that it needs to live in.

And then it kind of makes its way down to the end part of your intestine. And that's where the poop gets formed. And a lot of water gets taken out. Because otherwise, if that didn't happen, you just have diarrhea all the time. And that's not fun for anybody. So a lot of absorption happens there and more breaking down. And then what you end up with is

It's like the stuff that your body can't use, lots of fiber and stuff that will turn into poop. So that's sort of the very simple summary of what happens after you put food in your mouth.

Hi, my name is Spencer. I live in North Vancouver. I'm five and a half. How do people pee and poop? How does our body know what becomes poop and what becomes pee? Well, there are different systems. I mean, you've got the kidneys and the bladder are what are handling the liquids, and the intestine is what's making the poo. So you have separate systems.

My name is Rowan. I live in Lincoln, Massachusetts. I'm three years old. My name is Rosie. I'm seven years old and I live in Vietnam. My question is, why poop is poop?

always brown. That has to do with these substances that are secreted that are called bile and bilirubin. These are, it's kind of like, you know, dyeing a shirt. It's brown stuff and it dyes the material brown, basically. Bile is a substance that breaks down fats in your small intestine, and it's a yellowish-greenish color.

bilirubin is made when your red blood cells break down. It's yellow, and it's making its way out of your body with the rest of the waste. So those two substances mix with the fiber and fats and other food waste, and it all turns brown. Of course, your poop can range in color depending on what you eat,

If you've ever eaten beets, for example, that can kind of dye your poop red. And if you go to a party and eat cupcakes with a lot of extremely blue frosting, you might have green poop the next day. I am Sam. I live in Dublin, Ireland. My age is seven. Why do poos smell so bad? Well, I should say, I should start out by saying it doesn't smell bad to everyone if you have a dog.

Your dog is pretty excited about that smell. So for lots or flies, flies like that smell. It's like that's a place they want to go visit. So it's a little bit up to who you are in terms of whether you think it smells bad. But when food gets broken down from what you saw on your dinner plate, by the time it goes through your guts, it's broken down into much different things, very basic building blocks of food. And some of those

smell hydrogen sulfide um smelly substance there's a bunch of different very basic chemical pieces of poop that uh smell like well there's lots of different smells rotten eggs um and and and it's um

People think about that it might have been something, not to get into evolution here, but it's a substance that nobody should be eating because there's lots of, can be dangerous things in it. So if it smells really bad, that's a way to tell your brain, stay away. So we may have evolved to hate that smell because it can be dangerous stuff. But why does it have different scents?

It depends on what you're eating. So if you're eating a lot of meat, meat tends to break down products, the things that meat gets reduced to in your gut, those tend to be stinky. Vegetable stuff, not as much like the horses and deer and animals that

don't eat meat have a very different smell. So it's also some spices tend to really make a strange or interesting smell in your poop, but it's often meat products that produce the stink. You mentioned that not every creature thinks poop smells bad. Flies, for example, are

really like the smell. They're attracted to it. And Theo wants to know why. I'm five years old. I live in Bronson, Michigan. Why do flies like poop? They're not eating it so much as they're setting up housekeeping. They are moving in and finding a place to raise a family. That's what's going on with flies. And if you think about poop, it's warm and moist, which is

they like. And it's also full of proteins and fats and vitamins. It's a very, I mean, for them anyway, it's a delicious, nutritious substance that they can, when the babies hatch, when the larvae hatch and you have all those little maggots squirming around, poop is something for them to eat. So it's kind of

Room and board for the maggots. My name is Henry. I am seven years old. I live in Brooklyn. How many germs are in one ounce of poo? Oh, gosh. I'm going to say trillions. You know, I haven't done the counting myself, but just a crazy, crazy amount of bacteria. I'd have to check this, but I think by weight.

Not all the liquid in poop, but in the dry ingredients in poop, it's mostly bacteria. There's so many trillions of bacteria happily living in your gut, keeping you healthy, just doing their bacterial thing. It's so weird. There are like more of them than you, I think. Mary might not have done the counting, but you know who has? The Centers for Disease Control and Prevention. The CDC, as it's abbreviated, says each gram of poop has one trillionth

trillion germs. But Henry asked about an ounce, not a gram. So we need to do some math conversion. One ounce equals about 28 grams. So one ounce of poop has 28 trillion or so germs. We are just big bacteria farms, just production company going about its business in there. We do need them. Why are bacteria good for us? If you didn't have them, you would not be able to

get nutrition from your food for what that's the most basic thing. They break down food, you know, hamburger, an apple, an ear of corn, they break it down. So they have to break it down into really teeny tiny molecules and fats and proteins, things that the cells can take in and feed themselves with. So basically the bacteria are eating the food first and pooping out the things that we need to absorb to live.

So you're kind of living on bacteria poop. Your body is constantly replacing the bacteria you lose through digestion. And that's good because we need bacteria in our gut to help us stay healthy. And we need to poop regularly to stay healthy and comfortable too. The food you eat, your diet, can play an important role in how often you poop and how it feels when you do. Some of you have probably heard adults talking about needing to eat more fiber to stay regular.

To put that in more direct terms, regular just means pooping regularly and not getting constipated, where you feel like you need to poop but you can't get it out, or having diarrhea, where your poop is really liquidy. Fiber is often found in foods like fruits, vegetables, and whole grains. But what does that have to do with poop? My sister on the on-firm

Yeah, and I'm four years old. How does Fiverr make you poop? Hi, my name is William. I'm five years old, and I live in Princeton, Texas. And my question is, why does Fiverr make you poop? Well, because it's something that the bacteria in your guts don't break down all the way. It's too tough and too fragile.

Well, fibrous. The bacteria have a tough time breaking it down properly.

into the kinds of bits that can be absorbed and used by the body. So they just pass right on through. It's just the, you know, kind of the stuff that you'd throw in the compost bin. The stuff that you're not using and you have to empty the bin. That's the whole basis of pooping. Fiber helps your body in a number of ways. It becomes food for that good bacteria we talked about earlier, and it can help make your poop easier to get out of your body. Not too hard and not too soft.

Okay, so here's a question. Why do we have to poop in the first place? My name is Vivi. I'm five years old. I live in California, Los Angeles. And my question is, why do we have to go to the bathroom? Because otherwise we'd explode.

the compost bin would fill up and fill up and your gut would stretch. And guts are very stretchy, but at a certain point they couldn't stretch anymore and they would burst. And that's really bad because all those bacteria that are wonderfully healthy and good, if they get out of the tube first,

That's bad news because they could spread around different places in the body and set up housekeeping in a bad spot and then you would get an infection and it'd be bad, very, very bad. So you don't want your gut to burst and that's why you need to keep emptying it. It's like a garbage bag. If you keep stuffing stuff into a garbage bag at a certain point, it's going to burst and all the stuff's going to come out and that's a mess. Let's go out of this world for a minute.

But be warned, this answer is a little bit gross. Hi, my name is Georgia. I'm five years old. I live from Coatland on Hodge in New York.

How do astronauts go poop in space? Well, the early astronauts, Gemini and Apollo, those first space missions, like they just had this, it was a plastic bag with an adhesive ring, like a sticky, a sticky ring. Then you put it over your butthole and you would poop into the bag. And you had, because there was no gravity to pull the poop down towards the toilet, or in this case, the bag, you had a little pull,

fingers thing that you stuck your finger you had to like coax it down into the bag and the astronauts hated it i can see why yeah they hated it and the you know the space capsule spelled it smelled like a porta potty by the end of a mission so when nasa moved on to bigger spacecraft like the international space station for example now they have toilets but without gravity you can't flush the

because flushing requires water falling down into the toilet and whooshing the poop away. So now you have to come up with a whole different system. So it's basically airflow. So there's this powerful breeze blowing past your butt and coaxing the poop down into the toilet. So, and in order to keep it in the toilet, there's a little sliding roof that has to shut. And if it

That's not timed right. It could cut off the top of the poop. And that gives you a situation actually called decapitation, fecal decapitation. And then the poop would, you know, float around the spacecraft. And that was terrible because you had to be the one to chase it down. Also, it could gum up the airflow holes and the toilet wouldn't work. And if the toilet didn't work, then you had to go back to using the bag.

So, very complicated machine, the space toilet. I did warn you that it was going to get gross. But also, at least to me, pretty interesting. I never thought about how complicated it would be to figure out a bathroom system for astronauts in space. But it's clearly very important. I think that's just about enough poop talk. Wouldn't you agree?

One more thing before we move on, though. We've been using the word poop pretty consistently in this episode, but that's not the technical term. The technical word for poop is feces or fecal matter. And there are lots of other words people have come up with to try to make it sound a little more polite. In fact, there are some pretty creative expressions people have used to try to avoid having to say poop or feces. One of my favorites that the NASA toilet

designers used was they talked about the astronauts' contributions. So you could just say to your adult, I need to go make a contribution in the bathroom. Exactly. Yes, I'm making a contribution. Okay, that's enough of that. But I'm sorry to tell your adults who are listening, it's not the end of the episode. Coming up, we answer your questions about farts.

This is But Why, a podcast for curious kids. I'm Jane Lindholm. We've been throwing the rules of polite conversation out the window in this episode, but it's all in service of science and understanding our bodies. We're exploring our own alimentary canal. Do you remember what that is? It's the system of tubes that takes food from your mouth down through your esophagus, stomach, small intestine, large intestine, and out the other end of your body as waste.

Everybody poops. And we've gotten a lot of good, serious questions about why and how. So we're answering them today with science writer Mary Roach. But there's something else smelly that comes out of our bottoms that we also want to learn more about today. Farts. Not surprisingly, there's one burning question we keep getting. My name is Eric. I live on Bainbridge, Washington. I am nine years old, and my question is, why do farts stink?

Well, they smell because some of the things we eat and not all of them, some of the things we eat when they're broken down into little tiny bits and pieces that our body can use in the process, gas is created. And some of those gases like hydrogen sulfide are really stinky. So depending on what you eat.

you can have really stinky farts. A lot of the main gas in farts is hydrogen and it is odorless, doesn't stink. So a lot of farts don't stink. It just depends on what you eat. I was mentioning before, meats are, I mean, I eat meat and I actually, after I learned this, I kind of pay attention to that. I'm like, oh yeah, there's a meat fart. Yeah.

I'm 11 years old, and I'm from California, Los Angeles, Hollywood. Water farts always stink when you're not in the bathroom. But when I'm out here with my family, I just want to put in some toots. It smells so bad. I think you're just really, really tuned into it when you're out in public. You're like, oh my God, is this going to be a stinker?

So you're really, you're going to notice and it's embarrassing and you don't want to get caught. So I think you're just paying attention more. Why are they such different noises, though? I mean, you can have farts that make all kinds of sounds, from completely silent to a squeak, a honk, a low toot like a foghorn, a wispy breeze blowing by, or even something that sounds like someone talking. What's the deal? And how do sound and smell go together?

Part of it has to do with you. If you're by yourself and nobody's around, you're just going to blow one out. Just, I think, you know, the sides of your butthole just are kind of flapping around. And I think that's where you get the sound. And if it's just a tiny, it's often like the little squeakers, the little tiny amount that comes out. Um, and,

that's not going to be as noisy. There's one theory when I spoke to, there's one expert on farts who I spoke to when I was writing Gulp and his feeling was that the ones that really, the ones that are going like

that you're really pushing out. He felt like those, the gas is dispersed more, so it's not going to smell as much. Like spread out. Spread out. So sometimes the little squeakers where the little cloud of stink just comes out like a little cloud, you know, that floats around. And if it hits your nose, then, you know, then you're going to get a wallop of smell. So it's sometimes those silent but deadly. It's the little ones that don't make a noise. Right.

And that was his theory, that when you blow it out...

with gusto, that you're spreading those molecules out so they don't have as much smell in any one place that a nose might be. While we're talking about farts, why do people fart? My name is Finn. I am seven years old. I live in San Diego. Why do people fart? Hi, my name is Frankie. I come from Fangarehe, New Zealand.

I'm five. Why do farts come out of my bum? Again, it's to keep you from exploding. You

you know, your gut is a long, it's like a long balloon in a way. It's very stretchy, but it only stretches so far. So if you couldn't fart and say you ate a lot of food that produces a lot of gas, like bread, and if there was nowhere, no release valve, your, your butthole is like a emergency release valve. That means there's like a lot building up in there and it's time to get rid of it. So really farting is keeps you alive. Yeah.

It's a life-saving maneuver to fart because if you didn't fart, the gas would get to the point where your gut would burst like a balloon. And then all the bacteria in there would go all around your body and cause trouble and could kill you. So,

So farting is a healthy and beneficial activity. In that case, if I, you know, fart out loud at the dinner table or in the classroom, can I tell my teacher and my family...

Sorry, Mary Roach told me this is a life-saving maneuver I'm doing and you can't get mad at me for it. Absolutely. Absolutely. And if they say, and who is Mary Roach? You can tell them she is a well-known science writer and the author of Gulp! Adventures on the Elementary Canal. Thanks very much to Mary Roach for answering our questions today.

But I should say before we finish, and I think Melody would want me to emphasize this, talking about poops and farts or using kind of gross language or even farting out loud on purpose, you have to be really thoughtful about where and how you do that.

Different families and communities have different levels of tolerance for that kind of talk or different words that they find appropriate and inappropriate. And you don't want to be rude or crude or make people grossed out just for the sake of it. So maybe make sure you're saving your poop conversation for an appropriate time. Like right now. I

I promised you could make your fart noises again at the end of the episode if you listened all the way through. So here's your chance before you or your adults turn this podcast off. Ready? Go. Three, two, one, stop! That's it for this episode. If you have a question about anything, gross or not gross, have an adult record you asking it. It's easy to do on a smartphone using an app like Voice Memos. Then email the file to questions at butwhykids.org.

We can't answer every question we get, but we love hearing from you and knowing what's on your mind. But Why is produced by Melody Beaudet and me, Jane Lindholm, at Vermont Public. Our video producer is Joey Palumbo. Our theme music is by Luke Reynolds, and we're distributed by PRX. We'll be back in two weeks with an all-new episode. Until then, stay curious. From PRX.