How Much Does a Fart Weigh?


Flatus—the proper medical term for gas emitting from the intestines—has been examined at length in comedy, on YouTube, and in dorm rooms around the world. A fart's volume, however, is not often addressed. Farts consist primarily of nitrogen, hydrogen, carbon dioxide, oxygen, and methane. These gases have mass, which means farts could theoretically be measured for volume. But has anyone ever bothered? And if so, how?

Yes. And, gently. In 1991, gastroenterologists from the Human Gastrointestinal Physiology and Nutrition Department of the Royal Hallamshire Hospital in Sheffield, England published a paper in the trade journal Gut that attempted to quantify toot size. Their methodology was simple: take 10 volunteers, feed them 200 grams of baked beans on top of their normal diet, and measure their flatulence over a 24-hour period via rectal catheters.

Placed where the sun's ray cannot shine. MediQuip

To confirm their collection protocol was up to snuff, subjects sat in a bath with the rectal catheter inserted—the line led to a laminated gas bag—and farted. Since no bubbles were visible, they concluded the catheter was sealed.

The physicians determined that the average adult produces a median 705 milliliters of gas (nearly 24 ounces, or two soda cans’ worth) every day. Men and women passed equal amounts; farts tended to be more robust following a meal.

The farters varied widely in individual output, with a range of 476 ml to 1491 ml among the subjects during the 24 hours. The researchers noted that a singular fart, regardless of time of day, gender, or body size, was between 33 to 125 ml, with a median of 90 ml. That’s the equivalent of roughly three ounces of comedy.

According to Matthew Bechtold, M.D. a gastroenterologist and associate professor of Clinical Medicine at the University of Missouri, fart volume can be highly variable depending on both the amount of swallowed air and the matter produced by bacteria in the colon. Simple carbohydrates that are incompletely digested feed these normal bacteria, which then produce gases. “The main carbohydrate responsible for flatulence is raffinose, a sugar commonly found in cabbage and broccoli, which is poorly digested,” he says.

The study noted that volunteers on low-fiber diets reduced most of the fermentation gases expelled, lowering their fart volume to 200 ml for an entire day.

The researchers did not indicate whether any solid matter would—or should—be considered when evaluating fart mass. According to Bechtold, no fecal material typically escapes during a gas pass. “The anus does well at keeping solid material in while letting the gas out,” he says.  

The approximate size of your average fart.

With that settled, we posed another flatus-related query to Bechtold: If someone farted in cold weather with their pants down, could we visualize the fart similar to the way we see someone’s breath?

“Given the gas is contained in an environment of 98 degrees Fahrenheit just like the lungs, if gas is passed in a cold enough climate, it would likely be witnessed,” he says. “However, given that most patients are fully dressed with a barrier of pants between the anus and the outside environment, it generally goes unnoticed and diffuses rapidly in the air.”

Put another way: A fart is roughly the volume of an airport-approved travel bottle, and could be seen in cold weather if you were inclined to remove your pants in the name of science.

Big Questions
What Do Morticians Do With the Blood They Take Out of Dead Bodies?

Zoe-Anne Barcellos:

The blood goes down the sink drain, into the sewer system.

I am not a mortician, but I work for a medical examiner/coroner. During an autopsy, most blood is drained from the decedent. This is not on purpose, but a result of gravity. Later a mortician may or may not embalm, depending on the wishes of the family.

Autopsies are done on a table that has a drain at one end; this drain is placed over a sink—a regular sink, with a garbage disposal in it. The blood and bodily fluids just drain down the table, into the sink, and down the drain. This goes into the sewer, like every other sink and toilet, and (usually) goes to a water treatment plant.

You may be thinking that this is biohazardous waste and needs to be treated differently. [If] we can’t put oil, or chemicals (like formalin) down the drains due to regulations, why is blood not treated similarly? I would assume because it is effectively handled by the water treatment plants. If it wasn’t, I am sure the regulations would be changed.

Now any items that are soiled with blood—those cannot be thrown away in the regular trash. Most clothing worn by the decedent is either retained for evidence or released with the decedent to the funeral home—even if they were bloody.

But any gauze, medical tubing, papers, etc. that have blood or bodily fluids on them must be thrown away into a biohazardous trash. These are lined with bright red trash liners, and these are placed in a specially marked box and taped closed. These boxes are stacked up in the garage until they are picked up by a specialty garbage company. I am not sure, but I am pretty sure they are incinerated.

Additionally anything sharp or pointy—like needles, scalpels, etc.—must go into a rigid “sharps” container. When they are 2/3 full we just toss these into one of the biotrash containers.

The biotrash is treated differently, as, if it went to a landfill, then the blood (and therefore the bloodborne pathogens like Hepatitis and HIV) could be exposed to people or animals. Rain could wash it into untreated water systems.

This post originally appeared on Quora. Click here to view.

Big Questions
Why Does Asparagus Make Your Pee Smell Funny?

The asparagus has a long and storied history. It was mentioned in the myths and the scholarly writings of ancient Greece, and its cultivation was the subject of a detailed lesson in Cato the Elder's treatise, On Agriculture. But it wasn't until the turn of the 18th century that discussion of the link between asparagus and odorous urine emerged. In 1731, John Arbuthnot, physician to Queen Anne, noted in a book about food that asparagus "affects the urine with a foetid smell ... and therefore have been suspected by some physicians as not friendly to the kidneys." Benjamin Franklin also noticed that eating asparagus "shall give our urine a disagreeable odor."

Since then, there has been debate over what is responsible for the stinky pee phenomenon. Polish chemist and doctor Marceli Nencki identified a compound called methanethiol as the cause in 1891, after a study that involved four men eating about three and a half pounds of asparagus apiece. In 1975, Robert H. White, a chemist at the University of California at San Diego, used gas chromatography to pin down several compounds known as S-methyl thioesters as the culprits. Other researchers have blamed various "sulfur-containing compounds" and, simply, "metabolites."

More recently, a study demonstrated that asparagusic acid taken orally by subjects known to produce stinky asparagus pee produced odorous urine, which contained the same volatile compounds found in their asparagus-induced odorous urine. Other subjects, who normally didn't experience asparagus-induced odorous urine, likewise were spared stinky pee after taking asparagusic acid.

The researchers concluded that asparagusic acid and its derivatives are the precursors of urinary odor (compared, in different scientific papers, to the smell of "rotten cabbage," "boiling cabbage" and "vegetable soup"). The various compounds that contribute to the distinct smell—and were sometimes blamed as the sole cause in the past—are metabolized from asparagusic acid.

Exactly how these compounds are produced as we digest asparagus remains unclear, so let's turn to an equally compelling, but more answerable question:


Remember when I said that some people don't produce stinky asparagus pee? Several studies have shown that only some of us experience stinky pee (ranging from 20 to 40 percent of the subjects taking part in the study, depending on which paper you read), while the majority have never had the pleasure.

For a while, the world was divided into those whose pee stank after eating asparagus and those whose didn't. Then in 1980, a study complicated matters: Subjects whose pee stank sniffed the urine of subjects whose pee didn't. Guess what? The pee stank. It turns out we're not only divided by the ability to produce odorous asparagus pee, but the ability to smell it.

An anosmia—an inability to perceive a smell—keeps certain people from smelling the compounds that make up even the most offensive asparagus pee, and like the stinky pee non-producers, they're in the majority.

Producing and perceiving asparagus pee don't go hand-in-hand, either. The 1980 study found that some people who don't produce stinky pee could detect the rotten cabbage smell in another person's urine. On the flip side, some stink producers aren't able to pick up the scent in their own urine or the urine of others.

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