Is farting a sign your gut microbiome is happy?

Summary

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What's That Rash? – "Is farting a sign your gut microbiome is happy?"

ABC Australia | June 9, 2026

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Episode Overview

This lively episode, recorded live at World Science Festival Brisbane, tackles an age-old question with science and humor: "Is farting a sign your gut microbiome is happy?" Hosts Dr. Norman Swan and Dr. Chris Smith, alongside an engaged audience, use data, history, and genuine curiosity to demystify flatulence, gut health, and the surprising links between your diet, your microbiome, and your brain.

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Key Discussion Points & Insights

1. Flatulence 101: Science, Etymology, and Social Taboos

• Opening Gags and Setting the Stage:
  Chris introduces a whoopee cushion ("We bought it especially for this particular episode..." [00:49]), establishing the episode's lighthearted but informative approach.

• John’s Audience Question:
  The core question is posed:
  “Is flatulence a sign that the gut biome is well fed and happy? And will a happy gut biome really improve one's cognitive function?” [01:17]

• Fart Terminology:
  The hosts discuss why we say "flatulence" or "fart," tracing roots from Old English ("fjorden") and Latin ("flatulentis"). Chris quips:
  “The word fart comes from Old English and Old German...it was probably an onomatopoeia.” [02:03]

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2. What Actually Is a Fart?

• Biological Process:
  “A fart is the expulsion of gas from your anus and it's basically the excess gas from the bugs in your bowel… They produce hydrogen, methane, carbon dioxide.” (Dr. Norman Swan, [03:00])

• Notable Study:
  Chris references Michael Levitt’s 1998 research:
  “Between 106 mils on the lower end, up to 1600 mils—a litre and a half—of air.” [03:56]
  Smelliest elements (hydrogen sulfide, methane, etc.) were present in very small concentrations—just 50 parts per million per fart.

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3. Social and Humorous Misconceptions

• Invisible College of Experimental Flotology:
  Chris jokes about an online repository of "fart charts," including a (possibly not-so-scientific) observation that farting at dinner parties surges when “the ladies leave the table.” [04:34]

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4. Microbiome Deep Dive—Diversity, Diet, and Output

• What’s in the Microbiome:
  Norman explains, “In the microbiome, we have millions and trillions of organisms...there's bacteria, viruses, fungi, and strange organisms called archaea.” [06:01]

• Diet Impact:
  “A diet that is lots of vegetables, legumes...the Mediterranean diet...tends to produce more gas." (Dr. Norman Swan, [06:43])

  Chris: "So more gas is potentially a sign of a healthier diet.” [07:08]

• But... There’s a Limit:
  “Obviously, there's a limit to it if you're producing a huge amount...” (Norman, [07:12])

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5. How Much Farting Is “Normal”? Data from the Field

• CSIRO Study:
  Norman: “90,000 people downloaded the fart app and it recorded 471,000 farts...They ended up with 6,000 people with 360,000 farts.” [08:28]

  • Men vs. Women:
    “For this sort of middle group...two to seven farts a day, that was equal between men and women. But 'super farters' (nine or more), women.” (Norman, [09:29])
  • By Age:
    “31 to 35 year olds. God knows what they're doing. They’re eating a Mediterranean diet.” (Norman, [10:08])
  • By State:
    “Which state had the smelliest, most lingering farts?... Western Australia." (Chris, [10:52])
  • By Time of Day:
    “Morning, mid-morning and after dinner at night.” (Norman, [11:03])

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6. What Happens if You Hold It In?

• Physiology:
  “The gas has got to go somewhere...your bowel absorbs the gas, it goes right in your bloodstream to your lungs and then you burp it out.” (Norman, [11:37]) Chris: “Did you actually burp just then?” [11:56]

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7. Hydrogen’s Role & The Microbiome-Brain Connection

• Hydrogen Production:
  “One of the most abundant gases in a fart is hydrogen, and it has a really important role to play...hydrogen gets recycled in your bowel.” (Norman, [12:23])

  Chris jokes: “Would you recommend someone trying to [light a fart]?” [12:29]
  Norman: “Probably not.” [12:34]

• Does a Happy Microbiome Mean Better Brain Health?
  Norman clarifies:
  “A healthy microbiome, which is very diverse…produces a lot of different bioactive compounds, including short chain fatty acids...these go to the brain, settle inflammation and oxidative stress…there’s a lot of crosstalk between the bowel and the brain…” [13:26]

  “It turns out that a healthy diet does improve your cognitive function…and this diet…is called the MIND diet…similar to Mediterranean, but with fermented foods and berries.” (Norman, [14:23])

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8. Farts as a Warning Sign

• “Excessive flatulence can be a sign of problems…irritable bowel syndrome…it’s worth knowing whether you have it. The other is celiac disease…” (Norman, [15:22])

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Notable Quotes & Memorable Moments

• “The word fart comes from Old English and Old German...it was probably an onomatopoeia.” (Chris, [02:03])
• “The biggest farter produced over half a litre of hydrogen, which I think could be some sort of renewable energy source.” (Chris, [03:56])
• “Only a third of them were really stenchy farters, weren’t they?” (Norman, [04:34])
• “So more gas is potentially a sign of a healthier diet.” (Chris, [07:08])
• “Who produced more farts, men or women?” (Norman, [09:05]) – Audience laughs and discusses.
• “Western Australia...They reported farts of high stench and linger.” (Chris, [10:52])
• “The gas has got to go somewhere…your bowel absorbs the gas....and then you burp it out.” (Norman, [11:37])
• “A healthy diet does improve your cognitive function…and this diet…is called the MIND diet.” (Norman, [14:23])
• “Excessive flatulence can be a sign of problems...irritable bowel syndrome...celiac disease.” (Norman, [15:22])

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Important Timestamps

• 00:49: The whoopee cushion makes its debut.
• 01:17: John’s audience question sets up the episode’s main theme.
• 03:00 – 04:34: Explanation of the science of farts; classic research findings.
• 06:01 – 07:08: Microbiome composition and the impact of diet discussed.
• 08:28 – 11:03: Results from the monumental CSIRO fart study.
• 11:37: What happens when you ‘hold in’ a fart?
• 12:23: Significance of hydrogen in farts and gut health.
• 13:26 – 14:23: The gut-brain connection and the MIND diet.
• 15:22: When farting could spell trouble: signs of irritable bowel or celiac disease.

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Tone & Audience Experience

The episode is science-packed, cheeky, and disarming—turning a commonly embarrassing topic into an educational and candid health discussion. The hosts balance data and practical advice with contagious humor (“We’re going to blow hard today, Norman.” [02:54]), making the episode accessible and memorable for all listeners.

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Conclusion – Key Takeaways

• Farting is a natural sign of a working microbiome and, in moderation, often reflects a healthy, fibre-rich diet.
• Flatulence alone isn’t a catch-all indicator of cognitive health, but the diversity and health of the gut microbiome can have real effects on brain function.
• Too much gas—especially if sudden or accompanied by other symptoms—warrants consideration of medical issues like irritable bowel syndrome or celiac disease.
• And yes, Western Australia claims bragging rights for stinchiest farts—at least, according to the data!

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For more quirky science and health Q&A, the hosts encourage emails at [e-mail]. Tune in next week for even more “What’s That Rash?” explorations!

Transcript

[Narrator/Host]

This episode is brought to you by Google Health. Stop chasing someone else's definition of health. What matters is what's healthy for you. Google Health offers a new kind of coach built with Gemini for effortless tracking, sleep insights and holistic coaching tailored to you. Visit googlestore.com to learn more and start a new relationship with your health. Requires Google Account, Google Health App Internet and Google Health Premium subscription. Features subject to change. Availability and results vary. Not intended for medical purposes or works independently of Gemini apps. Check responses for accuracy.

[Host 1]

So you know how I love my musical apparatus for our chats? Norman?

[Dr. Norman Swan]

Yes.

[Dr. Chris Smith]

I've got my med Diet bell here

[Host 1]

on the desk with me today. I forgot to bring my harmonica and my xylophone because I'm an idiot, but I did bring an extra new friend.

[Dr. Chris Smith]

Would you like to hear it?

[Dr. Norman Swan]

Yes, I think I do. You're a ruby girl.

[Dr. Chris Smith]

It's a whoopee cushion. We bought it especially for this particular episode of what's that? Rash.

[Dr. Norman Swan]

Where we answer the health questions everybody's got. And this time we were farting in front of a live audience.

[Host 1]

That's right. This chat comes from our recent live show at World Science Festival, Brisbane. So this question came from John, who? The question itself was read out by a lovely audience member at our live show.

[Audience Member/John]

I am moved to ask a question of my own. We are urged to eat lots of fibre to nourish the gut and microbiome biome. Is flatulence a sign that the gut biome is well fed and happy? And will a happy gut biome really improve one's cognitive function?

[Dr. Chris Smith]

John, you've asked that question so well I'm going to give you a round of applause.

[Dr. Norman Swan]

Can we have the microphone back for a second? Why don't you just call flatulence for what it really is?

[Audience Member/John]

Ok. A fart.

[Dr. Norman Swan]

Very good. Thank you. Because I wasn't sure what you were talking about, to be honest.

[Dr. Chris Smith]

So on that, do you know, it's a little bit like, you know how we call cow meat beef and pig meat, pork and that sort of thing. And I don't know if anyone's heard this story before. The reason we would do this is because after the Norman Conquest, it was sort of fancier to speak in French. So around the table, you would say the French word for cow, which was like boeuf, which became beef, or you would say the fancy word for pig, which was like porcine. And so in a similar way, the word fart comes from Old English and Old German. The word was fjorden. Which meant to. Which meant to, like fart. It was probably an onomatopoeia. Whereas flatulent comes from the Latin flatulentis, which comes from a root meaning to blow. And we're going to blow hard today, Norman.

[Dr. Norman Swan]

We are. We're going to fertin a lot.

[Dr. Chris Smith]

Fertin. What is a fart?

[Dr. Norman Swan]

A fart is the expulsion of gas from your anus and it's basically the excess gas from the bugs in your bowel. So you eat all this food, it gets absorbed in the small intestine and then it goes into the large bowel, into the colon, and the bacteria in your bowel chew it up and the bacteria produce gas, they produce hydrogen, they produce methane, they produce carbon dioxide.

[Dr. Chris Smith]

Okay, so.

[Dr. Norman Swan]

And hydrogen.

[Dr. Chris Smith]

And hydrogen, which we'll come to later. There's actually quite a lot of research into farting. We'll get into some of it soon. But I did really enjoy this particular study that was done in 1998, where there was a US scientist called Michael Levitt and he used rectal tubes for a detailed study of fart compositions in six healthy women and 10 healthy men.

[Dr. Norman Swan]

Big study, Big study. Uncomfortable study.

[Dr. Chris Smith]

Would you like to know a rough volume of gas that was emitted from these people? Between 106 mils on the lower end, up to 1600 mils a liter and a half of air. The biggest farter produced over half a litre of hydrogen, which I think could be some sort of renewable energy source. The thing that really caught my attention, though, is that the smelly components of the fart were quite small. So together, hydrogen sulfide, methane, ethiol, which smells like rotten cabbage and the garlic, like dimethyl sulfide, on average were just 50 parts per million of each fart.

[Dr. Norman Swan]

And only a third of them were really stenchy farters, weren't they?

[Dr. Chris Smith]

Stenchy farters? I think there's some foreshadowing research that we will get to. But before we get to legitimate research, I have to introduce you the Invisible College of Experimental Flotology, which is a website that exists. When I first saw flatology, I was like, oh, is this some sort of flat earth society? No, it's theology, the study of flat u lence. And they've done some well, look, I don't know if the research is real. I don't really care. The charts are. The fart charts are amazing. Let's look at one, please. This. If you have very quickly decoded this chart, I'm very, very impressed. But basically, for those who haven't and for those who are Listening without the benefit of visuals. What you're looking at here is the rate of farts at a dinner party. And you'll notice that there's a particular peak at the time of the evening where the ladies leave the table. They looked at the. At the air quality during this time. So that's a little bit of a data point that you can drop around the dinner table, so to speak. So part of the question from John, who had such a beautiful voice, was about the microbiome. So we've talked a bit about what farts are, and I am very intentionally using the Germanic route here. We're not fancy, we're among friends. What about the macrobiome? What about the microbiome?

[Dr. Norman Swan]

In the microbiome, we have millions and trillions of organisms. We tend to think of bacteria, but there's bacteria, there's viruses, there's fungi, and then there's these really weird ancient organisms called archaea, which we don't really know too much about, but they're in there as well. So, really going back probably millions of years, we've got these bugs in our bowel, if you can call them bugs, and so there's this plethora, but it seems to be bacteria because they're more advanced in terms of their metabolism that produce the gases. And our microbiome is affected by what we eat. Coming back to the question, what we

[Dr. Chris Smith]

eat feels like we could take that a step further and have a reason to use some sort of.

[Dr. Norman Swan]

Yeah, well, it could be that. A diet that is lots of vegetables, legumes, what we call that diet.

[Dr. Chris Smith]

I think we would call it the Mediterranean diet. I feel like I'm driving through a grove of bellbirds. It's beautiful.

[Dr. Norman Swan]

So, yeah, it depends on what bacteria you've got and what they're eating. And they produce more gas when you're actually eating a healthier diet.

[Dr. Chris Smith]

Also, more gas is potentially a sign of a healthier diet.

[Dr. Norman Swan]

There's obviously a limit to it if you're producing a huge amount, so more

[Dr. Chris Smith]

than 1600 milliliters per day.

[Dr. Norman Swan]

So it's hard to measure. But there are diseases like Crohn's disease. There's an operation called fundoplication, which is to prevent reflux. And for some reason, a side effect of that operation is producing more gas. They don't understand why, but probably because it changes the microbiome. But essentially a healthy diet will produce more gas.

[Dr. Chris Smith]

Okay, so we've got oblacing saddles is right. Okay. You just said before that you don't really Know what's good, like normal? That some things can make you. If you're unhealthy in different ways that can produce more gas and less gas. What do we know about how many farts a day is normal?

[Dr. Norman Swan]

Well, we've got the CSIRO to thank for this, who provided. What's that rash with exclusive farting data. Farter further data from Australians.

[Dr. Chris Smith]

So this is the chart you start. This is the chart you start. Study that chart.

[Dr. Norman Swan]

Your fart app.

[Dr. Chris Smith]

App. And it's Dr. Brindle from CSIRO that we have to give credit to. And our thanks for letting us bring you this. What's that Ration Live show exclusive updated

[Dr. Norman Swan]

data and you're all sitting on the edge of your seats with. Well, you are one cheek up. 90,000 people downloaded the fart up the app and it recorded 471,000 farts. They had to, because they're CSIRO and they're good scientists, they had to exclude. So they wanted a reasonable sample of farts. Farts, Farts. And so they excluded everybody who recorded less than three days. So it had to be more than three days. The average was about 10 days of farts and they ended up with 6,000 people with 360,000 farts. So not bad data. So here's the question. Who produced more farts, men or women? Go on. Acclamation. Women. Women. Do you agree with that? No.

[Host 1]

No.

[Dr. Norman Swan]

Yes, men.

[Dr. Chris Smith]

I think we need a show of hands. Who reckons men produced more farts? Who reckons? I notice all the women have their hands up. Who thinks that women produce more farts? All men have their hands up. Interesting. Interesting.

[Dr. Norman Swan]

So for this sort of middle group of farts, that's two to seven farts a day, that was equal between men and women. But when they looked at the group that were producing nine or more farts a day, super farters, women,

[Dr. Chris Smith]

maybe they were more delicate, maybe they were more diligent in recording their data.

[Dr. Norman Swan]

Yeah, well, that's true. They could have been biased there. So which age group would you say? If I were to say, you know, young people, middle age, older people.

[Audience Member/John]

Yeah, old farts.

[Dr. Norman Swan]

So does the old fart thing hold true? Clearly this room thinks so.

[Dr. Chris Smith]

What did the data say?

[Dr. Norman Swan]

31 to 35 year olds. God knows what they're doing. And impressed. They're eating a Mediterranean diet. So here's the question. Which state in Australia had the smelliest, most lingering farts?

[Dr. Chris Smith]

This is an actual data point. If someone can answer this correctly, let's give them a magnet, yell out the state you think Tasmania. Someone said Tasmania. Someone said nt. Someone said Queensland. No one has said the correct answer yet. No, not act. Did anyone say Western Australia?

[Dr. Norman Swan]

One person said Western Australia.

[Dr. Chris Smith]

Western Australia. They reported farts of high stench and linger. I would have thought with a state that size, you would be able to get away from a smelly fart.

[Dr. Norman Swan]

And the time of day that you mostly fart. Well, it's sort of morning, mid morning and after dinner at night. Pretty much reflecting our insurance.

[Dr. Chris Smith]

Yeah, the ACONM type.

[Dr. Norman Swan]

So really valuable data there on flatology. Flatology.

[Dr. Chris Smith]

What I want to know then, Norman, given that we're normalising farting, we get a sense of these feelings.

[Dr. Norman Swan]

I'm just feeling a bit.

[Dr. Chris Smith]

What happens if it's not the right time and you just need to hold it in? Is that bad for you? Asking for a friend?

[Dr. Norman Swan]

So here's what happens when you hold it in. The gas has got to go somewhere because they continue to produce the gas. And what happens is your bowel absorbs the gas, it goes right in your bloodstream to your lungs and then you burp it out.

[Dr. Chris Smith]

Did you actually burp just then?

[Dr. Norman Swan]

I was trying to, but I didn't. Did you smell it?

[Dr. Chris Smith]

I heard it, yeah.

[Dr. Norman Swan]

Eventually gets out and comes out via the other end of your intestinal tract, your mouth.

[Dr. Chris Smith]

Incredible. Well, like I said before, there's some small amounts of compounds in your farts that make them smelly, highest stench and linger from wa, as we previously discussed. But one of the most abundant gases in a fart is hydrogen, and it has a really important role to play.

[Dr. Norman Swan]

It does. So it's not just being able to light your fart.

[Dr. Chris Smith]

As a doctor.

[Dr. Norman Swan]

Yes.

[Dr. Chris Smith]

Would you recommend someone trying to?

[Dr. Norman Swan]

Probably not.

[Dr. Chris Smith]

Probably not.

[Dr. Norman Swan]

Is it partly myth? I don't know. You have to know. You were a big hydrogen farter. So hydrogen is actually quite important because the bugs in your bowel use the hydrogen as part of their metabolic processes. So hydrogen gets recycled in your bowel. So it's quite important that you produce hydrogen. And contrary to the study you just quoted from Pennsylvania, they reckon it's about a liter of hydroge we can produce a day, but it does get recycled, so you're not farting blue flame the whole time.

[Dr. Chris Smith]

So to come back to John's question, John wants to know if flatulence is a sign that the biome is well fed. And will a happy gut biome help one's cognitive function? We haven't talked about cognitive function at all because we've been talking too much about the more Important topic of farting. But to come back to John's question, what's our answer?

[Dr. Norman Swan]

Our answer is, yes, it can, but not through farting. So a healthy microbiome, which is a very diverse microbiome, and the diet that we've been talking about,

[Dr. Chris Smith]

you guys, quicker.

[Dr. Norman Swan]

Of a very healthy, diverse microbiome, and that produces a lot of different bioactive compounds, including what are called short chain fatty acids. And these do go to the brain and they settle down inflammation and oxidative stress. But also there's this complicated communication between the bowel and the brain using the nervous system and indeed the immune system. So there's just a lot of crosstalk between the bowel and the brain, as you might imagine, since the brain needs the bowel to survive, we need the bowel to survive. So it's a very complex interrelationship, but it turns out that a healthy diet does improve your cognitive function. And the diet that really does this is called the mind. No, careful, careful. We need another science called the mind diet. The what M I N diet. And this diet is known to protect the brain, and it tends to be a bit like the Mediterranean diet, but there's a bias towards fermented foods and berries, particularly blueberries and strawberries.

[Dr. Chris Smith]

So the other words, the rich people diet. Well, thank you, John, for the question. One final piece of data before we go off this, which is all about acoustics. If you look at the screen, you will see a mathematical formula that shows us that simultaneous farts can sound like one single fart. And this is how you would calculate this. And to prove the point, I think if anyone here feels like they know how to make a. I would love to hear them all at once, please. One, two, three. Oh, come on. Okay, do this one, then do one of those. One, two, three.

[Dr. Norman Swan]

And I suppose one of the other takeaways from this is that excessive flatulence can be a sign of problems in your bowel. One is irritable bowel syndrome, and there's not a lot you can do about that, but it's worth knowing whether or not you have it. And the other is celiac disease, where you are truly gluten intolerant. And. And that might be a sign that you want to get checked for that, which is a specific set of investigations because you don't want to have celiac disease and not know it.

[Host 1]

Absolutely.

[Dr. Chris Smith]

Just goes to show that we can't

[Host 1]

be as comprehensive as we would always

[Dr. Chris Smith]

like to be on.

[Host 1]

What's that rash. There's always more to learn. And we love it when we get your emails as well. Our email address is thatrashbc.netau and we've had an email about our recent episode on progressive exercise. Norman from a few weeks ago. Ryan says, I don't go to a gym. I'm too shy for a public squat.

[Dr. Norman Swan]

Yes, we're going back to the fart episode here. I mean, okay.

[Dr. Chris Smith]

Mariah says.

[Host 1]

So rather than spend a fortune on more weights, I'll just push on with my efforts but with more time and reps. And thanks for the earlier episode regarding more time to exercise. I'm a 10pm lounge to myself type of exerciser. So between both episodes you've helped with my motivation and my back pain.

[Dr. Norman Swan]

Oh that's good, that's lovely.

[Host 1]

Thank you so much Ryan. Love thinking of you squatting in your lounge at 10pm Love it.

[Dr. Norman Swan]

Exercise. Sorry, abolish the thought.

[Host 1]

And some correspondence Norman from our other live show that was in the feed a few weeks ago on left handedness versus right handedness, Paul says I'm a

[Dr. Chris Smith]

lefty shout out Paul.

[Host 1]

So am I, but it's a lot more complicated than people generally think. Most tools, hammers, saws, etc. I use left handed. I can only write left handed so I am left eye dominant that I can only shoot, whether guns or arrows, left handed. And in fact my right eye can't even process what it sees down a scope if forced to use a right handed rifle. But Paul continues I play left handed at tennis, right handed at cricket and as far as I'm concerned it's the same grip on the bat and racket. Now I'm, I'm standing here in the studio, Norman, trying to arrange my hands around a bat and a racket. Paul is very multi talented and naturally fences left handed but can only throw a ball right handed. My left hand is useless for this.

[Dr. Norman Swan]

So Paul, I hope you've got well controlled aggression here with your swords and your guns but you know, carry on.

[Dr. Chris Smith]

Well.

[Host 1]

Paul has also been known to kick a rugby ball with his left foot but plays soccer right footed. I can only use scissors in my left hand but eat steaks with the knife in my right hand usually sometimes not. Paul, you sound like a true Renaissance man and I kind of like that you're mixing it up with your handedness along the way and I could have

[Dr. Norman Swan]

picked you as a red meat eater.

[Host 1]

What has that meant to me?

[Dr. Norman Swan]

Just leave it there I think.

[Host 1]

And Gary similar. Gary doesn't mention quite as many extracurriculars as Paul, but Gary says I'm right hand dominant, but I kick a football with my left foot. Always have. And changing has been something best not discussed in public. Well, Gary, now I just have so many more questions.

[Dr. Norman Swan]

Gary, you can write us a letter with a different name and we'll quote it.

[Host 1]

And of course, if you do write that letter, the email address is that rashabc.net au we'll see you next week.

[Dr. Chris Smith]

See you then.