Just about everyone gets the ‘tude toots. Lucky for you, intrepid physician Paul Auerbach decided in 1981 to research the phenomenon so mountain lovers would no longer have to suffer in silence, or decimate imaginary frog populations. In a letter to the editor of The Western Journal of Medicine, Auerbach and his colleague Dr. York E. Miller wrote:
We would like to report our observations upon a new gastrointestinal syndrome, which we shall refer to by the acronym HAFE (high altitude flatus expulsion). This phenomenon was most recently witnessed by us during an expedition to in the San Juan Mountains of southwestern Colorado, with similar experiences during excursions past. The syndrome is strictly associated with ascent, and is characterized by an increase in both the volume and the frequency of the passage of flatus, which spontaneously occurs while climbing to altitudes of 11,000 feet or greater.
Until recently, researchers believed HAFE was a simple case of Boyle’s Law: the volume of gas increases as the pressure decreases. In this case, lower air pressure allows the gas in your intestines to expand until it can’t expand any longer and must escape.
But a 2013 study published in the journal Medical Hypotheses suggests HAFE is a bit more complex. Australian researchers found the farts occur at altitudes as low as 5,900 feet, and that flatus frequency tends to peak around eight and 11 hours after a rapid ascent. Rapid meaning you got there in a day from a much lower altitude. In this study, subjects went from about 1,000 to 5,900 feet in 40 minutes. (Average post-ascent expulsions per person: 14.)
“We speculate that the lag results because the increase in gas volume is not so much from expansion, as one might intuitively expect according to Boyle’s Law, but more from diffusion of CO2 into the intestinal lumen from the bloodstream,” researchers wrote.
“We’ve got carbon dioxide dissolved in the bloodstream,” says lead researcher Dr. Graham Slaney. “As the atmospheric pressure reduces, the gas that’s dissolved in the liquid will come out of that liquid. So essentially in the bowels, you’ll have more gas that will diffuse across into the gut and expand, obviously causing flatus.”
So there you have it. If you’re planning a trip to the mountains, we advise against planning dates between eight and 11 hours after arrival.