The relationship between coffee and bowel movements has been known for a long time. That relationship usually has been tied to the stimulating effect of the caffeine in coffee. About 30% of coffee drinkers need to go to the bathroom after drinking their morning cuppa. Coffee’s impact on the gastrointestinal tract is among the 18 healthful reasons to drink coffee.

The caffeine theory sounds plausible except that researchers reported in 1990 that an increase in the need for a bowel movement following a person’s morning coffee occurred even when the coffee was decaffeinated.

On Sunday, researchers from the University of Texas reported that coffee, caffeinated or not, suppressed bacteria and increased muscle motility, or the ability of the gastrointestinal tract to contract and mix and propel its contents along.

The researchers fed rats with different concentrations of coffee for three days and then examined the animals’ fecal matter for bacteria. Among the rats fed a 1.5% coffee solution, bacteria counts fell. The counts fell even more among rats fed a 3.0% coffee solution. Both caffeinated and decaffeinated coffee had a similar effect.

Xuan-Zheng Shi, lead author of the study and associate professor of internal medicine at the University of Texas Medical Branch-Galveston, said, “When rats were treated with coffee for three days, the ability of the muscles in the small intestine to contract appeared to increase.” The authors note that further research may determine if coffee could be an effective treatment for post-operative constipation when a patient’s intestines stop working after abdominal surgery.

The research did not determine whether the decrease in bacteria favored good gut bacteria (firmicutes) or bad (enterobacteria). However, the rats’ coffee ingestion did increase the ability of the lower intestine and colon muscles to contract. This does not mean that people should drink more coffee. There are added health risks from too much coffee consumption, and coffee drinkers should be on the lookout for the 20 symptoms of too much coffee intake.

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