Quick answer: Coffee makes some people poop because it stimulates the colon. In a 1998 study, caffeinated coffee increased colon activity about as much as a meal and 60% more than water; decaf had a smaller effect. Only some people react: in a 1990 survey, 29% said coffee gave them the urge to go.
Coffee has two well-known bathroom effects: the urge to poop and more trips to pee. The first is a direct effect on the gut. The second is caffeine’s mild diuretic action, which turns out to matter much less than people think.
In this guide 6 sections
Why does coffee make you poop?
Researchers have measured this directly. In the 1990 study in Gut, 29% of 99 young adults said coffee made them want to go. In the people who reported this, black coffee increased movement in the last part of the colon within four minutes, and the effect lasted at least 30 minutes. Decaf did the same in that study, but a plain cup of hot water did not, so it isn’t just the warm drink.
The 1998 study measured colon pressure in 12 healthy people. Caffeinated coffee stimulated the colon about as much as a 1,000-calorie meal, 60% more than water and 23% more than decaf. So caffeine plays a part, but other compounds in coffee seem to contribute too.
Is coffee a diuretic?
Mildly. MedlinePlus describes caffeine as a diuretic that helps your body get rid of extra salt and water through urine. A diuretic is anything that increases how much you urinate.
Does coffee dehydrate you?
Not at moderate amounts. In a 2014 study, 50 men who were regular coffee drinkers spent three days drinking four 200 ml cups of coffee a day and three days drinking the same amount of water. Their hydration markers, total body water and 24-hour urine volume were no different between the two. The authors concluded that moderate coffee hydrates about as well as water in habitual drinkers.
The study only covered moderate intake in men who already drank coffee. People who rarely have caffeine, or who take a large dose, may notice more of a diuretic effect.
What are the downsides of too much coffee?
Dehydration isn’t the main concern. The FDA lists these effects of too much caffeine:
- Fast heart rate and palpitations
- Higher blood pressure
- Insomnia and disturbed sleep
- Anxiety and jitters
- Upset stomach and nausea
- Headache
The FDA cites 400 mg of caffeine a day, about two to three 12 oz cups of coffee, as an amount not generally associated with negative effects in most healthy adults. More in signs you’re drinking too much coffee.
What about coffee enemas?
Coffee enemas are sometimes promoted for constipation or “detox”. Drinking coffee is all that’s needed for the effect described above, and we don’t recommend enemas. If constipation keeps coming back, see a doctor rather than trying one.
Frequently asked questions
Why does coffee make me poop but not other people?
Only a minority of people get the effect: 29% in the 1990 survey. In the study, people who reported it showed a measurable response in the colon, and people who didn’t report it showed none.
Does decaf make you poop too?
It can. In the 1990 study, decaf also increased colon activity in people who were sensitive to coffee. In the 1998 study, decaf had a smaller effect than regular coffee.
Does coffee count toward my daily fluids?
Yes, in moderation. The 2014 study found moderate coffee hydrated habitual drinkers about as well as water.
Coffee can also cause gas and bloating for some people; see can coffee cause bloating? For the wider picture, read is coffee good for you? and how long coffee stays in your system.
This article is for general information and isn’t medical advice.
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