By Anne Marie Helmenstine, Ph.D.
Your morning cup of coffee can jumpstart your day, but it may also send you on a beeline for the bathroom, both to pee and possibly to poop. Whether you experience the diuretic effect (so you need to urinate) or colon-stimulating effect (so you have a bowel movement) depends on your personal biochemistry and whether you're a regular coffee-drinker or not. Here's what scientists know...
How Coffee Relates to Poop
A study published in the gastroenterology journal Gut verified some people experience colon stimulation within minutes of consuming a cup of coffee. Not everyone reacts this way, so if you don't drink a cup of joe in the morning to 'get started' in that manner, you're not alone. If coffee does make you poop, how does it work?
Scientists aren't quite certain, but have ruled out some possibilities and identified other explanations. First, it's probably not the stimulating effects of caffeine, since the laxative effect is seen with decaf as well as high-octane joe.
Coffee promotes the release of the hormone gastrin, which stimulates the secretion of gastric juice and increases colonic motor activity. Activating the colon may stimulate peristalsis, leading to the purgative effect.
Is Coffee a Diuretic?
The caffeine in coffee is a stimulant. Generally, stimulants increase urine production. If coffee acts as a diuretic, drinking it will make you need to urinate more frequently, dehydrating you slightly. Dehydration can lead to constipation, which is the opposite of what some coffee drinkers experience.
However, coffee isn't necessarily a diuretic! A 2003 study published in the Journal of Human Nutrition and Dietetics found that regular coffee drinkers develop a tolerance to the effect and don't excrete more urine, even if they drink 2-3 cups of coffee per day.
So, if coffee doesn't act as a diuretic for you, you may be more susceptible to the laxative effect of the brew. Another factor could be psychological, since bodily functions tend to adapt to a daily pattern. Thus, if you always start your day with a cup of coffee and a bathroom break, your physiology may become accustomed to the routine.
However it works, scientists have verified coffee's biochemical ability to send people to the toilet, just not necessarily for the same reason as each other.