Stools: their flotation in the toilet would depend on our intestinal bacteria

We can imagine: if our stools float in the toilet, it is probably because they partly contain trapped gases. But where do these gases come from? Why do some people have stools that float and others have stools that sink?

Crucial questions if any, obviously, since researchers have very recently provided some answers. In a new study, published at the end of October 2022 in the journal Scientific Reports (Source 1), a team from the Mayo Clinic in Rochester (Minnesota, USA) discovered that the ability of stools to float on the surface results from the composition of the intestinal microbiota, or intestinal flora.

The team worked here on mice, divided into two groups: a group was said to be “germ-free”, in other words mice whose intestine does not contain any microbiota, and a group of “colonized” mice whose digestive system contains bacteria. The “germ-free” mice then received a fecal transplant, to colonize the digestive system with gut bacteria.

By simultaneously monitoring microbiota densities and [vitesse] intestinal colonization in mice [ayant reçu une transplantation fécale]we provide the first direct evidence of a causal relationship between intestinal microbial colonization and fecal flotationwrite the researchers.

It should be noted that this is a fortuitous discovery, because the team was initially interested in the intestinal microbiota, and not in the flotation of the excrement of the mice.

Because after fecal transplantation, the mice initially devoid of microbiota saw their stools become “floating” whereas they had previously flowed steeply.

By introducing microorganisms into the gut of germ-free mice, we have conclusively demonstrated that intestinal colonization of microbiota is a prerequisite for feces to float”, write the scientists in conclusion.

Intestinal microbiota and floating stools: further studies needed


The gases resulting from the fermentation of the food that we consume are evacuated periodically in the form of flatulence, but can sometimes be trapped in the stools, thus reducing their density, the researchers further explain. The density and buoyancy of the stool also depends on our lifestyle and the foods consumed, since some are transformed into gas more than others by our microbiota. The composition and diversity of our microbiota could also come into play in this strange fecal equation.

The authors of the study succeeded in identifying two bacteria – Bacteroides ovatus and Bacteroides fragilis – which are known to produce gas in the intestine. However, other experiments will be necessary to know more about this.

Note that having stools that float is associated with irritable bowel syndrome (or irritable bowel), at least in the mixed form, with alternating diarrhea and constipation.

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