Every coffee enthusiast knows that a trip to the bathroom is to be expected after a cup of morning brew.

The question is, how and why is coffee linked to bowel movement? To help them solve the mystery, scientists fed coffee to rats and observed the effects on the bowel and feces.

Coffee And Poop

In a study presented at the Digestive Disease Week 2019, researchers confirmed that drinking coffee does boost muscle motility in the intestines as well as decrease bacterial growth in the gut. However, it does not appear to be caffeine behind these effects.

"When rats were treated with coffee for three days, the ability of the muscles in the small intestine to contract appeared to increase," explained Xuan-Zheng Shi, PhD, study lead author and an associate professor in internal medicine at the University of Texas Medical Branch, Galveston. He added that these effects are independent of caffeine, since both regular coffee and decaffeinated brew both caused similar impact on the gut.

Shi and his colleagues studied the changes to bacteria when the fecal matter was exposed to coffee in a petri dish, then observed the composition of the feces after the rats consumed a variety of concentrations of coffee over three days. There are also changes noted in the muscles of the intestines and colon when exposed to coffee.

The Findings

Findings showed that the growth in the bacteria and microbes in fecal matter on a petri dish declined with 1.5 percent solution of coffee. An even lower growth resulted from a 3 percent solution of coffee.

Interestingly enough, decaffeinated coffee produced the same results.

"That's really interesting, because that means coffee could be an antibacterial agent, and we could see this again with decaffeinated coffee," Shi said in an interview with Gizmodo. "But that we need to study more—why coffee could have this suppressing effect on the microbiome."

In the analysis after the rats consumed coffee for three days, the overall amount of bacteria in the feces decreased as well. However, the researchers noted that it's not necessarily a positive effect, since the study did not indicate whether the changes affected good bacteria or bad bacteria.

The rats' muscles in the lower intestines and colons also showed increased ability to contract after a period of consuming coffee, which allows the feces to move through faster.

According to the study authors, their findings encourage further research to find out whether coffee can be recommended as an effective treatment for post-operative constipation.