How does food turn into poop?

Summary

But Why: How Does Food Turn into Poop?

Podcast Information:

• Title: But Why: A Podcast for Curious Kids
• Host: Jane Lindholm, Vermont Public
• Description: A child-led curiosity podcast where kids ask questions about the world, and experts provide answers.
• Episode: How Does Food Turn into Poop?
• Release Date: November 15, 2024

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Introduction

In the But Why episode titled "How Does Food Turn into Poop?", host Jane Lindholm explores the intricate journey of food through the human body, addressing common and quirky questions posed by curious children. The episode features renowned science writer Mary Roach as the guest expert, who delves into the science of digestion, the role of bacteria, and even the complexities of waste elimination in space.

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Understanding the Digestive Process

Mary Roach begins by outlining the fundamental stages of digestion, simplifying the complex biological processes into digestible (pun intended) explanations suitable for young listeners.

• Chewing and Swallowing:

  [02:57] Mary Roach: "First thing you have to do is chew it up so it's kind of a mushy thing that you can swallow... then you form it into a swallowable thing called a bolus."

• Stomach Breakdown:

  [03:54] Mary describes how the stomach further deconstructs food into a "liquidy porridge" before it moves into the small intestine for nutrient absorption.

• Nutrient Absorption and Waste Formation:

  [04:32] Jane Lindholm: "Most of the nutrients you get from your food are absorbed into your body in the small intestine."

  [04:53] Mary explains, "A lot of water gets taken out... what you end up with is stuff that your body can't use... turns into poop."

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Detailed Q&A with Curious Kids

The heart of the episode lies in the engaging Q&A segment where Mary Roach addresses various questions from children, each shedding light on different aspects of digestion and waste.

1. How Does Food Turn into Poop?

• Question by Matteo (8, St. Paul):

  [03:37] "How does your food turn into your poop?"

• Mary's Explanation: Mary outlines the journey from chewing to nutrient absorption, emphasizing the role of the small intestine and water absorption in forming feces.

  [05:47] "A lot of absorption happens there and more breaking down, and then what you end up with, it's like the stuff that your body can't use, lots of fiber and stuff that will turn into poop."

2. How Do People Pee and Poop?

• Question by Spencer (5.5, North Vancouver):

  [05:47] "How do people pee and poop?"

• Mary's Response: She differentiates between the urinary and digestive systems, explaining that "the kidneys and the bladder handle liquids, and the intestine is what's making the poo."

  [06:00] "Well, there are different systems. I mean, you've got the kidneys and the bladder... the intestine is what's making the poo."

3. Why is Our Poop Brown?

• Questions by Rhode (3, Lincoln, Massachusetts) and Bowsey (7, Vietnam):

  [06:14] "Why is our poop brown?"

• Mary's Clarification: She attributes the brown color to bile and bilirubin, combining with fiber and fats to produce the typical hue.

  [06:35] "That has to do with these substances that are secreted called bile and bilirubin."

4. Why Do Poo and Farts Smell?

• Question by Sam (7, Dublin, Ireland):

  [07:38] "Why do poo smell so bad?"

• Mary's Insight: She explains the chemical breakdown of food leading to smelly compounds like hydrogen sulfide, which act as evolutionary signals to avoid harmful substances.

  [07:38] "Hydrogen sulfide, smelly substance... maybe we've evolved to hate that smell because it can be dangerous stuff."

• Additional Question by Eric (9, Bainbridge, Washington):

  [19:20] "Why do farts stink?"

• Mary's Explanation: The smell from farts is due to certain foods breaking down into odorous gases during digestion.

  [19:29] "Some of the things we eat... a gas is created. Some of those gases, like hydrogen sulfide, are really stinky."

5. Why Do Flies Like Poop?

• Question by an unnamed child (5, Bronson, Michigan):

  [09:28] "Why do flies like poop?"

• Mary's Answer: Flies are attracted to poop not for eating but for breeding grounds, offering warmth, moisture, and nutrients for larvae.

  [09:45] "They're not eating it so much as they're setting up housekeeping... poop is something for them to eat."

6. How Many Germs Are in One Ounce of Poop?

• Question by Henry (7, Brooklyn):

  [10:29] "How many germs are in one ounce of poo?"

• Mary's Response: Mary estimates "trillions" of bacteria, a figure later clarified by Jane Lindholm using CDC data.

  [10:37] "Oh, gosh. I'm gonna say trillions... just a crazy, crazy amount of bacteria."

  [11:36] Jane Lindholm: "The CDC says each gram of poop has 1 trillion germs. So one ounce of poop has about 28 grams, trillion or so germs."

7. How Does Fiber Make You Poop?

• Questions by Anya (4, Lancaster, Pennsylvania) and Liam (5, Princeton, Texas):

  [13:07] "How does fiber make you poop?"

• Mary's Explanation: Fiber isn't fully broken down by gut bacteria, aiding in forming bulkier, easier-to-pass stool.

  [13:27] "The bacteria in your guts don't break [fiber] down all the way... they just pass right on through."

8. Why Do We Have to Poop?

• Question by Titi (5, Los Angeles, California):

  [14:17] "Why do we have to go to the bathroom?"

• Mary's Insight: Pooping prevents the gut from becoming overly stretched and bursting, averting bacterial infections.

  [14:28] "Because otherwise we'd explode... you don't want your gut to burst."

9. How Do Astronauts Poop in Space?

• Question by Georgia (5, Cotton on Horton, New York):

  [15:21] "How do astronauts go poop in space?"

• Mary's Detailed Account: Mary recounts the evolution of space toilets from simple bags with adhesive rings to complex airflow systems on the International Space Station, highlighting challenges like "fecal decapitation."

  [16:01] "It's a very complicated machine, the space toilet."

10. Why Do People Fart and Why Are They Noisy?

• Questions by Finn (7, San Diego) and Frankie (5, Bangara Heights, New Zealand):

  [22:38] "Why do people fart?"

• Mary's Response: Farting serves as a vital release of excess gas to prevent gut rupture, comparing it to an "emergency release valve."

  [22:59] "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."

• Additional Discussion on Noises: Mary explains that the sound of farts varies based on the force and dispersion of gas, with quieter farts often being "silent but deadly."

  [21:15] "One expert felt that when you blow out with gusto, the gas disperses more, so there's not as much smell in any one place."

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The Role of Bacteria in Digestion

Mary Roach emphasizes the symbiotic relationship between humans and gut bacteria, vital for breaking down food into usable nutrients.

[12:20] "If you didn't have them, you would not be able to get nutrition from your food."

She describes the gut as a "bacteria farm," where trillions of bacteria work tirelessly to digest food, outnumbering human cells in the body.

[11:42] "We are just big bacteria farms, just production, production companies going about its business in there."

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The Importance of Fiber

Jane Lindholm elaborates on fiber's role in digestive health, explaining how it aids in maintaining regular bowel movements and preventing conditions like constipation and diarrhea.

[14:01] "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."

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Pooping in Space: A Closer Look

Astronauts' unique challenges with waste elimination illustrate the complexities of human biology in microgravity environments. Mary details early methods and the advancements leading to the current airflow-based systems, which, despite improvements, still face issues like poop floating uncontrollably if not managed correctly.

[16:02] "They're very complicated machines, the space toilets."

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Farting: More Than Just a Noise

The episode transitions to discuss farts, addressing common misconceptions and the physiological necessity behind them. Mary clarifies that while farts are often a source of humor or embarrassment, they play a crucial role in maintaining digestive health.

[22:38] "Farting keeps you alive. It's a life-saving maneuver."

She also touches on the social aspects, advising listeners to be considerate about when and where they discuss or produce fart sounds.

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Conclusion

But Why successfully demystifies the seemingly taboo topic of digestion and waste, transforming it into an engaging and informative discussion tailored for young minds. With Mary Roach's expertise, listeners gain a comprehensive understanding of the digestive system, the essential role of bacteria, and the complexities of waste management both on Earth and in space.

Jane Lindholm wraps up the episode by reinforcing the importance of respectful conversation around such topics while encouraging continued curiosity.

[25:13] 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."

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Key Takeaways

• Digestive Stages: From chewing to nutrient absorption, each step is crucial in transforming food into usable energy and waste.
• Bacteria's Role: Gut bacteria are essential for breaking down food, aiding in nutrient absorption, and maintaining overall health.
• Fiber's Benefits: Dietary fiber facilitates smoother digestion and regular bowel movements by acting as food for beneficial bacteria and adding bulk to stool.
• Waste Management: Pooping and farting are vital bodily functions that prevent the buildup of harmful substances and gases.
• Space Challenges: Managing waste in space poses unique engineering and biological challenges, highlighting the complexities of human biology beyond Earth.

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Notable Quotes

• [02:57] Mary Roach: "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."
• [04:32] Jane Lindholm: "Most of the nutrients you get from your food are absorbed into your body in the small intestine."
• [07:38] Mary Roach: "We may have evolved to hate that smell because it can be dangerous stuff."
• [10:37] Jane Lindholm: "The CDC says each gram of poop has 1 trillion germs. So one ounce of poop has about 28 grams, trillion or so germs."
• [22:38] Mary Roach: "Farting keeps you alive. It's a life-saving maneuver."

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Final Thoughts

This episode of But Why not only answers children’s burning questions about digestion and waste but also emphasizes the importance of these processes in maintaining health. By addressing topics often considered "gross" with scientific accuracy and humor, the podcast fosters a healthy curiosity and encourages open discussions about the human body.

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Remember: If you have more curious questions, have an adult record you asking them and send the recording to [e-mail]. Stay curious!

Transcript

[Jane Lindholm]

Support for but why comes from Progressive Insurance. Do you ever think about switching insurance companies to see if you could save some cash? Progressive makes it easy to see if you could save when you bundle your home and auto policies. Try [e-mail] Progressive Casualty Insurance Company and affiliates. Potential savings will vary. Not available in all states. 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 Boatwy. 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 how 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.

[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 so I can remember what they've said. And then I take all that information and put it in a book.

[Jane Lindholm]

Mary Roach has written eight books, and one of them is of particular interest to our topic. It's called Adventures on the alimentary canal.

[Mary Roach]

That was the point at which I became something of a weirdo expert on the things that happen between your mouth and your butt.

[Jane Lindholm]

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.

[Curious Kid]

I'm Matteo, I'm eight years old, and I'm wondering, how does your food turn into your poop? I'm Solomon and I'm 6 and I live in St. Paul. How does food turn into poop?

[Mary Roach]

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.

[Jane Lindholm]

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.

[Mary Roach]

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. 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. That's not fun for anybody. So a lot of absorption happens there and more breaking down, and then what you end up with, 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.

[Curious Kid]

Hi, my name is Spencer. I live in North Vancouver. I'm five and a half. How do people pee and poop?

[Jane Lindholm]

How does our body know what becomes poop and what becomes pee?

[Mary Roach]

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.

[Curious Kid]

My name is Rhode. I live in Lincoln, Massachusetts. I'm three years old. Why is our poop brown? My name is Bowsey. I'm seven years old, and I live in Vietnam. My question is why poop is almost always brown.

[Mary Roach]

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.

[Jane Lindholm]

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.

[Curious Kid]

I am Sam. I live in Dublin, Ireland. My age is 7. Why do poo smell so bad?

[Mary Roach]

Well, I should say. I should start out by saying it doesn't smell bad to everyone. If you have a dog, I think your dog is pretty excited about that smell. So for lots. Or flies. Flies like that smell. It's like, that's. Ooh. 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, smelly substance. There's a bunch of different, very basic chemical pieces of poop that smell like. Well, there's lots of different smells. Rotten eggs and. And. And it's. You know, people think about that. It might have been something, you know, not to get into evolution here, but you Know, it's a substance that nobody should be eating because there's lots of, you know, 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.

[Jane Lindholm]

But why does it have different scents?

[Mary Roach]

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 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.

[Jane Lindholm]

You mentioned that not every creature thinks poop smells bad. Flies, for example, really like the smell. They're attracted to it, and Thea wants to know why.

[Curious Kid]

I am five years old. I live in Bronson, Michigan. Why do flies like poop?

[Mary Roach]

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 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. 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. It's kind of room and board for the maggots.

[Curious Kid]

My name is Henry. I am seven years old. I live in Brooklyn. How many germs are in one ounce of poo?

[Mary Roach]

Oh, gosh. I'm gonna 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, dry 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. They're like more of them than you.

[Jane Lindholm]

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 1 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 grams. Trillion or so germs.

[Mary Roach]

We are just big bacteria farms, just production, production company going about its business in there.

[Jane Lindholm]

We do need them. Why are bacteria good for us?

[Mary Roach]

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.

[Jane Lindholm]

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?

[Curious Kid]

My name is Anya. I'm from Lancaster, Pennsylvania, and I'm 4 years old. How does fiber make you poop? Hi, my name is Liam. I'm five years old, and I live in Princeton, Texas. And my question is, what does Piper never make you poop?

[Mary Roach]

Well, because it's something that your. The bacteria in your guts don't break down all the way. It's. It's too tough and. And too, well, fibrous. The bacteria have a tough time breaking it down 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.

[Jane Lindholm]

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?

[Curious Kid]

My name is Titi. I'm five years old. I live in California, Los Angeles. And my question is, why do we have to go to the bathroom?

[Mary Roach]

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, 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.

[Jane Lindholm]

Let's go out of this world for a minute. But be warned, this answer is a little bit gross.

[Curious Kid]

Hi, my name is Georgia. I'm five years old. I live from Cotton on Horton, New York. How do astronauts go poop in space?

[Mary Roach]

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 fingers thing that you stuck your finger. You had to, like, coax it down into the bag. And the astronauts hated it.

[Jane Lindholm]

I can see why.

[Mary Roach]

Yeah, they hated it. And the, you know, the space capsule spelled 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 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 then 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 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. 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 hole 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.

[Jane Lindholm]

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.

[Mary Roach]

One of my favorites that the NASA toilet designers used was they talked about the astronauts contributions.

[Jane Lindholm]

So you could just say to your adult, I need to go make a contribution in the bathroom.

[Mary Roach]

Exactly, yes, I'm making a contribution.

[Jane Lindholm]

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. Farts. Not surprisingly, there's one burning question we keep getting.

[Curious Kid]

My name is Eric. I live On Bainbridge, Washington. I am nine years old and my question is, why do faults stink?

[Mary Roach]

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, a 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. You know, a lot of the, the main gas in farts is hydrogen and it is odorless, doesn't stink. So a lot of farts don't stink. You know, it's just depends on, 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.

[Curious Kid]

I'm 11 years old and I'm from California, Los Angeles, Hollywood. My farts always stink when you're not in the bathroom. But like, when I'm like out here with my family, I just want to, like, put in some toots. It like, smells like so bad.

[Mary Roach]

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.

[Jane Lindholm]

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?

[Mary Roach]

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 that, you know that's, 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, his feeling was that the ones that really, the ones that are going like that, you're really pushing out. He felt like Those that the, the gas is dispersed more so it's not going to like spread out, spread out. So, so sometimes the little squeakers where the little cloud of stink just, it comes out like a little cloud, you know that, 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. And that was his theory that, that when you blow it out with gusto that you are spreading those molecules out so they don't have as much smell in any one place that a nose might be.

[Jane Lindholm]

While we're talking about farts, why do people fart?

[Curious Kid]

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 Bangara Heats, New Zealand. I'm five. Why do farts come out of my bum again?

[Mary Roach]

It's to keep you from exploding. 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 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 keeps you alive. 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 farting is a healthy and beneficial activity.

[Jane Lindholm]

In that case, if I 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.

[Mary Roach]

Absolutely, absolutely.

[Jane Lindholm]

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 Alimentary 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 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. 3, 2, 1.

[Mary Roach]

Stop.

[Jane Lindholm]

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 questionsutwhykids.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.

[Mary Roach]

From PRX.