Like opening the curtain or stepping into the shower, having a cup of coffee in the morning turns people on — in more ways than one. This satisfying drink boosts our energy level with a dose of caffeine. For many people, it quickly and often stimulates bowel activity, leading to an urgent need to evacuate.
Given the popularity of coffee, it’s surprising how little we know about how it affects the gastrointestinal tract, said Dr. Robert Martindale, professor of surgery and medical director of hospital nutrition services at Oregon Health and Science University.
Some studies on the topic – which tend to be small, limited and from some time ago – have suggested that it’s probably not the caffeine that makes you want to go to the bathroom. For example, an article published in 1998 concluded that decaffeinated coffee exerts a stimulating effect on the colon similar to caffeinated coffee, which a cup of water does not.
Coffee is a complex beverage that contains over a thousand chemical compounds, many of which have antioxidant and anti-inflammatory properties. And it’s not easy to determine how they affect the intestines.
One thing we do know is that coffee doesn’t affect everyone in the same way. In a study published in 1990 in the journal Gut, 92 young adults completed a questionnaire on how coffee affects their bowel movement habits. Only 29% of them said that drinking “makes you want to have a bowel movement”, and the majority, 63%, were women. But Martindale said the percentage of people who have a bowel reaction after drinking coffee is likely much higher in the general population — he estimated that to be the case for 60% of his patients — and he didn’t notice any difference between men and women. .
We also know that the intestinal reaction to coffee can be rapid. In the same study, some volunteers let a pressure-sensing probe be inserted into their colon to measure bowel muscle contractions before and after drinking a cup of coffee. Among those who said that coffee generally stimulated bowel movement, the tube indicated a significant increase in pressure within four minutes of drinking coffee, whereas non-responsive people showed no change in colonic activity.
The fact that having a cup of coffee can stimulate the opposite end of the gastrointestinal tract in a matter of minutes means, Martindale said, that the stimulus “probably goes through the gut-brain axis.” That is, the arrival of coffee in the stomach sends a message to the brain, which then “stimulates the colon to say, ‘It’s good to empty ourselves, because something’s coming up,'” he explained. The coffee itself would travel through the intestines much more slowly, probably taking at least an hour to travel the long way from the stomach, through the small intestine, and then into the colon.
This communication between the stomach, brain and colon, called the gastrocolic reflex, is a normal response to food intake. But coffee seems to have a disproportionate effect. A study published in 1998 found that 230 ml of coffee stimulated colon contractions similar to those induced by a 1,000-calorie meal. Researchers theorize that coffee’s gut-brain communication is likely caused by one or more of the many chemical compounds contained in coffee and possibly mediated by some of our hormones that play important roles in the digestive process, such as gastrin or cholecystokinin, both of which which can rise in level after drinking coffee.
The mechanism may not yet be clear, but the effects of coffee on the gut may help some people, including patients recovering from certain types of surgery. Weakened bowel function is common after abdominal surgery, for example, which can lead to bloating, pain, and an inability to expel gas or tolerate food. A 2020 analysis combined the results of seven clinical trials and found that drinking coffee helped patients who had undergone colorectal or gynecological surgery to tolerate solid food for an average of ten and 31 hours, respectively, earlier than would have been the case without drinking the beverage. . Coffee also reduced the time spent before your first bowel movement after surgery by an average of 15 to 18 hours.
“A sip or two of coffee can be enough. You don’t have to drink a lot,” said Martindale, who routinely offers his patients a cup of coffee the morning after surgery.
For his patients who suffer from chronic constipation, Martindale also suggests that they drink coffee in addition to other dietary modifications. And he said it’s not uncommon for patients who have given up coffee for one reason or another to say to him, “Doctor, I can’t go to the bathroom without having coffee first.”
Nutritionist Sonya Angelone, a spokeswoman for the Academy of Nutrition and Dietetics, says people shouldn’t rely too heavily on coffee to maintain regular bowel function. If the person is constipated, he explained, “it’s not because they have a coffee deficiency.” To avoid constipation, she recommends consuming more fruits and vegetables, which are high in fiber, increasing your fluid intake and engaging in more physical activity. “What I find with a lot of people is that they don’t start their day with a good dose of fiber,” she said. Strained coffee contains a small amount of fiber – about one gram per 230 ml cup.
For some people, coffee causes stomach upset and loose bowels, as well as side effects linked to too much caffeine, such as insomnia, rapid heartbeat and headaches, Angelone said.
The Food and Drug Administration says it is safe for most people to consume 400 mg of caffeine a day — the amount found in four to five cups of coffee. But it must be remembered that people metabolize coffee in very different ways, so this threshold can vary from person to person. “Unlike other foods, coffee is one of those things that, if it hurts you, you can tell,” Angelone said.
For the rest of us, though, coffee can be part of a comforting morning routine, waking us up in a variety of ways.
Translation by Clara Allain
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