Coffee Doesn't Just Help You Poop. It May Change The Physiology in Your Gut.

We can usually feel the effects of coffee in the body pretty quickly.

If you're a regular coffee drinker, that first sip can promptly clear the morning fog and get your day going.

Not long after, coffee drinkers also tend to experience a different side effect: their bowels get going, too.

But new research published in the journal Gut Microbiology suggests regular coffee consumption may have a few other interesting effects on your gut.

We're all keen to know what might be going on inside our bodies as a result of our coffee habits, but it's surprisingly difficult to pin down the details.

Scientists from institutions in Denmark, Singapore, and Belgium repurposed data from 61 participants involved in an observational study, PRIMA (which stands for 'toward Personalized dietary Recommendations based on the Interaction between diet, Microbiome and Abiotic conditions in the gut').

The researchers investigated whether habitual coffee intake (based on an eight-day food diary and biomarkers in urine) was associated with gut microbiota composition (assessed using samples of participants' poop) and gastrointestinal physiology measures like colon contractions (recorded via a smart pill swallowed by 50 of the participants).

"Small intestinal pH was also significantly lower in frequent coffee drinkers, compared to rare coffee drinkers," the authors report.

And in general, the more caffeine metabolites there were in a person's urine sample, the more bacteria there were in their poop, too.

That correlation held up for all four caffeine metabolites tested, which means it's unlikely to have occurred due to random chance.

But that wasn't the case for some of the other results.

The 48 people who drank coffee frequently – defined in this study by the low bar of consuming coffee on four or more of the eight days – had more microbial species richness in samples of their poop than the 13 who drank it rarely (i.e., less than three of eight days).

Even that result wasn't particularly strong, statistically speaking, especially because of the low sample size.

The gut microbiome results were also fairly inconclusive.

At first, it seemed the gut microbiomes of frequent coffee drinkers had a distinct profile. Species of the bacterium Lawsonibacter were particularly abundant, along with Slackia and an unclassified taxon in the family Eggerthellaceae.

Scientists already knew Lawsonibacter's growth can be stimulated by coffee in lab conditions, and that it tends to grow more prolifically in the guts of coffee drinkers.

But in this study, when the microbiome results were adjusted using a statistical tool designed to decrease the rate of false discovery, these differences between frequent and rare drinkers did not hold up, though Lawsonibacter and the Eggerthellaceae taxon were still linked to how much coffee people drank in other analyses.

Scientists would have to conduct this research with a much, much larger sample size to know for sure if there are any meaningful patterns here.

And as to whether any of those effects would be good for you? The study doesn't really go there.

"It is important to note that this study was originally not intended to investigate the effects of coffee consumption," the authors write.

However, they add, "the relationships observed provide valuable indications for future research on the interplay between the gut microbiota, gut physiology, and coffee – one of the most consumed beverages in the world."

The findings are reported in Gut Microbiology.