How often do you poop? Yes, this is a very TMI question, but an important one. Constipation, where you’re pooping less than three times a week, is one of the most common gastrointestinal complaints resulting in 2.5 million doctor visits every year, according to Johns Hopkins Medicine.
Aside from drinking more water or eating more fiber, some research suggests the gut microbiome could play a key role in constipation, particularly for individuals with functional constipation, a more chronic form of the condition. However, not everyone with functional constipation experiences relief with a probiotic, and right now, probiotics aren’t even recommended blanketly as a treatment for constipation.
A new study published Tuesday in the journal Cell Host and Microbe could help shed some light on the relationship between the microbes in our gut and how often we poop. Researchers in Hong Kong and China argue that what makes a good poop-inducing probiotic may hinge on whether the bacteria can digest a plant fiber called arabinan. They found that if gut microbes contained the genes responsible for arabinan digestion — called the abfA gene cluster — mice and humans with functional constipation pooped better and more frequently.
While the study is a proof-of-concept, connecting this ability with treating functional constipation addresses “one critical challenge in the probiotic field,” which is finding what exactly makes a good probiotic, Shi Huang, one of the study’s authors and an assistant professor of microbiology at the University of Hong Kong, said in a press release. He adds it could also be used as a “simple yet powerful biomarker for gastrointestinal diseases.”
Microbial enzymes to the rescue
For their study, Huang and his colleagues in China examined a common type of probiotic called Bifidobacterium longum (or B. longum) that lives in the intestines and is one of the first bacteria to colonize our guts after birth.
They collected 185 poop samples from 354 healthy individuals — from newborns to centenarians — across China. They isolated several different strains of B. longum and transplanted them into mice given a medication, called loperamide, to induce functional constipation.
Based on how well the mice could poop with their new microbial additions, the researchers found some strains of B. longum were more helpful than others. In particular, those bacteria contained a cluster of genes that direct the digestion of arabinan, a dietary fiber found in various fruits and vegetables. Humans can’t digest arabinan well, so we rely on specific gut microbes to break apart the chemical bonds linking the fiber’s sugar molecules using enzymes, in this case, arabinofuranosidases, which are encoded by B. longum’s abfA cluster.
In additional experiments to cement their finding, Huang and his colleagues examined what would happen if they just gave constipated mice arabinan in their chow or the fiber combined with a normal strain of B. longum or one with the genes edited out. Just arabinan without the probiotic or with the edited one didn’t change anything. Mice getting arabinan combined with the unedited B. longum pooped more and with quicker gut transit times (i.e., how long it takes a specific food to travel through the digestive tract, which is about 30 to 40 hours in non-constipated individuals).
Interestingly, the researchers saw that giving the probiotic without arabinan didn’t help with constipation. They say this suggests some sort of synergistic effect where you need the fiber and a bacteria encoding abfA genes together to get the bowels moving.
Oral supplement or fecal transplant?
Before you take this as a sign to stock up on Bifidobacterium longum before the holiday eating marathon commences, know that this bacteria isn’t the only one that helps with constipation.
The researchers found other bacteria with the abfA cluster in their genomes. These include microbes from families like Bacteroides, Enterococcus, and Pediococcus. In mice with functional constipation, giving them specific bacteria from these families that are found in the human gut, like Bifidobacterium breve, Pediococcus pentosaceus, and Bacteroides nordii, also helped improve the animals’ constipation on par with B. longum.
While these findings are promising, they still need to be validated in human-based clinical trials, both to prove efficacy and to find the best way to deliver the probiotic, such as an oral supplement or via a fecal transplant.
In one small double-blind, randomized trial the researchers did, twenty-eight elderly participants with functional constipation who got beneficial strains of B. longum were pooping better and more frequently than those who received the placebo or the strain without the genes. In a separate experiment, germ-free mice with functional constipation who were given a fecal transplant from six healthy donors showed a noticeable improvement in their symptoms. Mice who received transplants heavy on the abfA-containing bacteria had more metabolites believed to be beneficial for the digestive tract, like acetate and butyrate.
No doubt, constipation is a debilitating discomfort. But the search for a probiotic ensuring a regular poop schedule is more so crucial for brain health. A 2023 meta-analysis found that chronically constipated folks had “significantly worse cognition” (the equivalent of three years of additional aging) compared to everyday poop-goers.
Here's to hoping we can one day enlist our gut bacteria to keep our digestive tracks running smoothly and a bit more punctually.
