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How Big Is A Fart? Somewhere Between A Bottle Of Nail Polish And A Can Of Soda

The questions kids ask about science aren’t always easy to answer. Sometimes, their little brains can lead to big places adults forget to explore. With that in mind, we’ve started a series called Science Question From A Toddler, which will use the curiosity of kids ages 5 and younger as a jumping-off point to investigate the scientific wonders that adults don’t even think to ask about. The answers are for adults, but they wouldn’t be possible without the wonder only a child can bring. I want the kids in your life to be a part of it! Send me their science questions. They may serve as the inspiration for a column. And now, our question …

Q: How much space does a fart take in your body? — Inbal R., age 5

Placed under the microscope, even the dullest grain of sand develops a personality. So it goes with farts. (Or “flatulence,” as they say in the scientific literature.) Farts may seem largely interchangeable, but each one is special. Even just your own farts are a circus sideshow of intestinal gas: big ones, little ones, stinky ones, oddly fresh ones. There is not enough scientific evidence to say that no two farts are alike — but you can rest assured that they are a riot of diversity.

As a result, it’s impossible to say exactly how much space a generic fart takes up in the body. I can, however, tell you about the range of specific farts, as captured in scientific experiments. For instance, a 1997 study of 16 Americans found a volume-per-fart range of 17 milliliters to 375 milliliters.1 Imagine a bottle of nail polish — that’s a rough analogy for the volume of the daintiest of poots. Now imagine a can of soda. That’s the volume of a really big stinker. Your body is a wonderland.

But there are another couple of questions floating around this data. First, obviously, “How does one collect a fart?” And I’ll get to that in a bit. But second, and perhaps more important, is this: “Why study the gas volume of farts?” That’s a really interesting question if for no other reason than the fact that Dr. Michael Levitt, a researcher at Minneapolis Veterans Affairs and the grande sieur of fart research, doesn’t think there’s much value to the data. “It’s just physiological fact,” he told me. It’s interesting to know the volume of a fart, but it doesn’t have a lot of deeper meaning.

So people just measured the volume of farts and continue to measure the volume of farts — Levitt was quantifying intestinal gas and writing about its chemical makeup back in 1968 — for, if you’ll pardon me, shits and giggles? Not exactly. It turns out that the value of knowing the volume of a fart, and the larger volume of gas in the intestine, lies not in what those measurements tell us — but in what they don’t tell us. Specifically, the volume of gas in your intestine tells us next to nothing about medical issues such as bloating and distention. The latter don’t appear to be caused by the former.

It’s true. A 2009 study compared the volume of gas in the gut and bowels before and after an episode of serious bloating. In that study, researchers took CT scans of patients’ abdomens. Intestinal gas shows up in these scans because its molecular density is different from those of the bones and organs and muscle and empty abdominal cavity around it. Because they know the density of the gas, researchers can pick out the spots where it is. Each spot shows up in the scans as an obese teal blob, floating between the ribs and the pubic arch. Because they know the area each pixel of the CT image represents, the scientists can calculate the volume of gas contained in the blobs.

Like the length of Anne Rice novels over time, the people in this study got bigger but not more substantive. Their bodies really did get wider about the tum when they felt bloated, but there wasn’t a big shift in the amount of gas in their guts — and definitely not enough to account for the increase in girth. Nor was the amount of gas in their guts, either before or after bloating, all that different from the amount in the guts of the blissfully bloat-free.

It’s weird. But it’s a finding that’s been replicated over and over. Other than in a small minority of people with really rare bowel disorders, gas doesn’t cause bloating, and farting won’t relieve it, Levitt told me. Fernando Azpiroz, chief of the department of digestive diseases at Spain’s Autonomous University Hospital Vall d’Hebron, another scientist who has spent years researching intestinal gas, agreed.

Now there is a caveat here. To quote a different 2009 paper, “Beans, beans, the musical fruit, The more you eat, the more you toot.”2 Certain foods, beans included, produce more easily fermentable residues as they break down in the stomach and intestines. More fermentation means more gas, so the “flatulogenic foods” really will increase the volume of gas in your gut and in your farts. In 2012, for instance, researchers took healthy volunteers and those who suffered from chronic gastrointestinal problems, fed them either a neutral or fart-inducing breakfast, and then put a catheter up each of their anuses to collect farts and transfer the gas to a machine that measured the volume of those farts in real time. The volunteers were hooked up this way for six hours after each meal, like if Tom Six of “Human Centipede” had abandoned directing horror films for life as a dairy farmer. (I told you we’d get to this eventually.)

The result: Beans for breakfast really do mean more farts and a higher volume of gas farted — from a mean of about 260 milliliters in six hours on the neutral breakfast to upward of 660 milliliters post-beans. (Bad news for fart-shy Brits?) But there wasn’t much difference in the volume of farts produced by the healthy people and those produced by the folks prone to bloating, even though the latter reported more discomfort.

So what gives? The going theory is that people who experience a lot of problems with bloating and farting — like those who have irritable bowel syndrome — are actually suffering from a nerve disorder that causes hypersensitivity to pain, said Bruno Chumpitazi, director of the neurogastroenterology center at Texas Children’s Hospital. There’s an overlap between people who have IBS and those with other kinds of pain disorders such as fibromyalgia and chronic pelvic pain, he said. And he told me tests using an inflatable balloon inserted into the colon have shown that it takes less inflation to make people with IBS feel symptoms such as pain, bloating and discomfort.

But the bloating is real, right? It can be measured. So there must be more going on than just a broken-down relay between brain and butt. Azpiroz has a theory about that — one that grew out of looking at all those CT scans of distended abdomens. There is a visible difference between the bloated and the nonbloated, but it’s not gas. Instead, it’s the position of the diaphragm, a sheet of muscle stretched under the lungs that aids in breathing. When patients feel bloated, their diaphragms have dropped down, pushing their stomachs out. Azpiroz said he suspects that it’s a learned behavior — a physical re-adjustment in response to the discomfort caused by hypersensitivity of the abdominal nerves. It’s something that, he says, can be fixed. Basically, instead of Gas-X, people with chronic bloating need to relearn how to hold their diaphragms high. Biofeedback, a system that uses electronic monitors to show patients what their bodies are doing and teach them how to consciously control it, can help.

And nobody would have known any of this if scientists hadn’t decided to find out how much space a fart took up in the body.

FiveThirtyEight: What your poop says about you


  1. The gas for these farts would be compressed and, thus, take up a touch less space while still inside the body.

  2. Yes, seriously. If you can get yourself a full copy of that paper, it really is worth reading. Figure 2 alone is a masterpiece.

Maggie Koerth was a senior reporter for FiveThirtyEight.