Why Does Coffee Make You Poop With Regularity?

OK, we admit that this is not one of the great medical mysteries of all time. It is intriguing, though. You might think that researchers have far more important things to do than try to figure out can coffee make you poop, and if so, why? One plausible hypothesis rests on gut microbes. A recent study found that they respond to coffee consumption.

Changes to Microbiome Might Explain How Coffee Could Make You Poop

An estimated two-thirds of American adults drink coffee every day. Now scientists have an idea why coffee is so popular. (The relationship with regular poop was not really part of the study question, we admit.) People who drink coffee derive psychological benefits that seem to be mediated by changes in the microbiome of the gut.

Researchers recruited 31 coffee drinkers (3 to 5 cups daily) and 31 people who do not drink coffee for a detailed study (Nature Communications, April 21, 2026). The composition of their gut microbiota was compared, with some striking differences appearing between those who did and those who did not drink coffee. Coffee drinkers had more diverse microbiomes. The scientists suggest that “coffee affects the gut microbiome independently of diet.”

Baseline tests assessed the mental and gastrointestinal health of all volunteers. Coffee drinks appeared to be more impulsive, in general, than abstainers. They were also somewhat more reactive emotionally. There were, however, no striking differences in cortisol levels between the groups.

No Coffee for Two Weeks

Then the coffee drinkers abstained from coffee for two weeks. During this time, the investigators noticed changes in their behavior (less impulsivity, more vigilance) and their gut microbiota.

After two weeks, coffee drinkers were once again provided with the beverage. Half of the volunteers got regular caffeinated coffee and the other half got decaf. Neither the researchers nor the participants knew who got which beverage. Non-coffee drinkers did not participate in this part of the experiment. The coffee-drinking volunteers reported less stress and depression once they were drinking coffee again, whether the coffee had caffeine in it or not.

Investigators also noticed changes in the balance of gut bacteria. with more bacteria generally considered positive inhabitants. People drinking decaf had improvements in learning and memory, possibly due to the polyphenols. Those getting caffeine in their mugs reported less anxiety but better attention and vigilance. The scientists note that coffee is much more than a caffeine delivery mechanism.

Perhaps because of its impact on the microbiome, coffee consumption also has an effect on immune responses. Coffee drinkers initially had lower levels of CRP, a measure of inflammation. These rose during the no-coffee period, along with TNF-alpha, another inflammatory marker. Once people started back on coffee, these levels returned toward baseline, whether the coffee contained caffeine or not.

The researchers note

“…coffee, regardless of caffeine content, supports cognitive, psychological, immune, and metabolic health in distinct but complementary ways.”

These scientists noted that not being able to measure stool transit time was a weakness of their study. Other scientists have looked at that, however, because of the implications for could coffee make you poop. It turns out that investigators have been struggling over this coffee conundrum for years. Several years ago, gastroenterologists presented a plausible explanation at a prestigious conference.

Coffee Restriction in the Hospital Was a Problem

Q. Coffee has kept me regular for years, though I don’t know why. Recently I was in the hospital for open-heart surgery. Every day in the hospital, the nurses plied me with stool softeners which, unfortunately, failed to move me.

I laughingly asked for coffee one day, saying it would surely work, and one nurse was kind enough to slip me a small cup. It did its job!

I spent another 18 days in the hospital where cajoling for more coffee did no good. Neither did double the amount of stool softeners relieve me. Going home was such a relief–in all ways.

A. When surgeons work on the gastrointestinal tract, it often causes “postoperative ileus.” That means intestinal motility slows down or stops for several days after surgery.

Medical Research Supports Post-Operative Coffee Consumption

A review of the medical literature in Gastroenterology Research and Practice (June 8, 2022) concludes that “postoperative coffee consumption shortened the time to first defecation following elective colorectal surgery.” A recent systematic review found that post-op patients chewing gum or drinking coffee defecated sooner (Journal of Gastrointestinal Surgery, June 5, 2023). On the other hand, taking caffeine did not seem to help.

Because you were in the hospital following open-heart surgery, coffee may have been forbidden. Doctors may worry that caffeine can stimulate the heart and could increase the risk for irregular beats.

On the other hand, a meta-analysis of 10 prospective studies reported that “coffee consumption had a trend toward reducing the risk of AF [atrial fibrillation] in a dose-response manner” (Frontiers in Cardiovascular Medicine, July 6, 2022).  Of course, every patient in the hospital should follow doctors’ orders.

Coffee Makes Him Go to the Bathroom

Q. I have found that my body reacts in a very predictable manner to my morning cup of coffee. Usually within 5 to 10 minutes I have to go to the bathroom. Is it the caffeine or something else in coffee that stimulates the bowels?

Does the Caffeine in Coffee Make You Poop?

A. You are not the first person to notice this effect. We used to think the caffeine was responsible, but scientists have shown that both regular and decaf coffee stimulate colon activity (Gut, April 1, 1990).  Caffeinated coffee does seem to have a stronger effect, however (European Journal of Gastroenterology & Hepatology, Feb. 1998).

How Many People Are “Moved” by Coffee?

The small study in the journal Gut cited above reported that 29 percent of the volunteers in their study claimed “that coffee induced a desire to defecate.” That could be right, but we would need to see much larger numbers to find that stat convincing. There were only 99 volunteers willing to participate in that research. The actual number could be substantially higher for all we know.

Does the Acid in Coffee Make You Poop?

Some scientists have attributed the laxative effect of coffee (regular or decaf) to its acid content. Chlorogenic acid can stimulate acid production in the stomach. The theory goes that this effect in turn triggers intestinal movements. So far, though, the data are not convincing.

Will the Magnesium in Coffee Make You Poop?

Some people suggest that coffee is high in the mineral magnesium. Everyone knows that magnesium has a laxative action. Just think Milk of Magnesia (magnesium hydroxide). A 2 oz cup of espresso has almost 50 mg of magnesium. But a regular cup of coffee has only about 7 mg of magnesium. That is not enough to get things moving.

What Really Makes Coffee Send You to the Bathroom?

Scientists have tested coffee in rats and found that both decaf and high-test increase the contraction power of intestinal muscle contractions. There are purported to be over 1000 different chemicals in coffee; hence the complex flavors and unique aroma. The researchers at the University of Texas, Galveston, did not identify which specific chemicals in coffee stimulate muscle movements within the digestive tract.

Coffee and the Microbiome:

The coffee treatments also changed the composition of the rats’ gut microbes, though no one is quite certain what that means for digestive health. One possible application of the coffee discovery is in the hospital, of all places.

When patients undergo abdominal surgery, they frequently develop something called post-operative constipation. When surgeons handle your intestines, the tissues tend to revolt by not resuming normal contractions for awhile. There are also the anesthetics, muscle relaxers, pain meds and the immobility of recovery. If coffee helps get the intestinal tract moving again, perhaps someday doctors will prescribe a cup of coffee in the days following abdominal surgery.

The investigators reported their research at a conference, Digestive Disease Week (DDW) 2019.

Share your own experience with coffee and trips to the bathroom in the comment section.