How did life come into being? Are we the only ones in the universe? Why does some excrement float and bob in the toilet while others sink? These are the huge mysteries that keep us awake at night, and one of them has finally been answered by chance. It is, indeed, the one about poop.
For years, we’ve had no idea why some dung floats and others sink like an anchor. Theories imply that greater fat content in the feces may contribute to the enhanced seaworthiness observed in floaters.
When one 1972 study published in The New England Journal of Medicine examined the stools of 33 healthy subjects (nine with floating stools, 24 with sinking stools, and six patients with fatty stools), they discovered that when the gas within their stools was “compressed by positive pressure,” all floaters sank (smushing up the poop).
“After degassing, previously floating and sinking stools had similar specific gravities, indicating that the floating or sinking propensity of such stools depends on differences in gas rather than fat content,” the researchers wrote, adding that the fatty poop was less dense than the others, but this was due to an increase in water rather than fat content.
“Thus, stools float because of an increased content of gas or water (or both); the floating stool should not be considered a sign of steatorrhea [increased fat content in poop].”
All of that, while interesting, doesn’t really explain the cause behind the difference in gas and water content. But recently, a team studying mice that had been made to be germ-free noticed something unusual about the mouse poop. While around 10 percent of healthy humans produce floaters consistently, this percentage is far higher in mice at around 50 percent. The team, who published their work in Scientific Reports, noticed that the poop of germ-free mice tended to sink.
“Our serendipitous finding of ‘sinker’ and ‘floater’ feces in TFS [Trump’s fixative phosphate-buffered solution] in germ-free and gut-colonized mice, respectively, led to the question of whether gut colonizers were fundamentally linked to the genesis of fecal floatation phenomenon,” the team write in their study.
Investigating further, the team took gut bacteria from healthy mice and put them into the stomachs of germ-free mice. Sure enough, their poops began to float too.
“By introducing microorganisms into the gut of germ-free mice, we have conclusively demonstrated that gut colonization of microbiota is a pre-requisite for feces to float.”
Though they stress that more study is needed to determine which gut bacteria causes the floatation – by introducing them individually to germ-free mice – and analysis of human poop is also needed, they did identify a few species of bacteria that were associated with floating poops.
“In fact, we identified Bacteroides ovatus to be the most enriched species in our analysis which has been positively correlated with flatulence and anal gas evacuation in human patients. Further, we also identified Bacteroides fragilis which is known to produce hydrogen gas in the gut.”
The study is published in Scientific Reports.