In fact, for decades, science has been asking the question why the feces of some people usually swim in a water-filled toilet bowl, while it immediately sinks in others: an estimated 10 to 15 percent of the population should belong to the first group. There has been a thesis on this since 1972; according to it, the swimming properties are supposed to be related to the gas content of the digestive products. Previously, this was mainly attributed to the fat content of the stool. Nagarajan Kannan from the Mayo Clinic in Rochester and his team have now probably finally been able to confirm the gas-based assumption, as they report in "Scientific Reports".
As the working group had noticed, the mice that was bred without intestinal flora always produced feces that went down in the water. On the other hand, half of all peers with normal microbioma also produced stool, which swam on top. This aroused the researchers' interest, which therefore injected intestinal bacteria from normal mice or two young women. The animal treated in this way also produced floating feces.
"Now there are no more doubts about what makes the stool float: the gas of intestinal microbes, not swallowed air or other causes, " says Kannan. A closer examination of the upwelling faeces also showed that they had several gas-producing bacteria, such as Bacteroides ovatus and Bacteroides uniformis. Both also lead to increased methane production and more frequent flatulence in humans. However, it is still unknown which gas quantities the various microbes contribute and thus who gives the decisive impetus for the buoyancy. This is to be determined by further tests.
It is also unclear whether the swimming properties could say something about general intestinal health in humans, according to the scientists. The composition of the intestinal flora is controlled, for example, through nutrition, the general environment or the type of birth of the respective person. All of these factors must be taken into account in the analysis.
The 1972 thesis was probably based on a conversation between gastroenterologist Michael Levitt of the University of Minnesota Hospitals and his student William Duane, who revealed that his chair would always float. A short time later, Duane delivered a stool sample, which the two researchers compressed, after which she then sank in the water. They then collected test material from 33 people, nine of whom produced floating feces. When Levitt and Duane degassed it under pressure, the material also sank. At that time, the researchers already suspected that the intestinal flora was the trigger: two samples had very high methane contents, which must have been caused by insufficient digestion of carbon-rich food. Only the final proof was still pending.
