Why Coffee Makes You Poop, According to a Dietitian

coffee on toilet

We've all been there, folks. That first sip of coffee at work and BAM! You gotta poop. You have no choice but to do the unholy thing in the communal toilets, and blame it all on Rick. But why? 

We spoke with Jacqueline Aizen (aka Jacqueline Shimmiezz), registered dietitian and professional belly dancer (apt!) about why, exactly, the roast brews up your gut. Here's what she had to say:

Why does coffee make you poop? What's the science behind it for the layman?

Caffeine stimulates the central nervous system (CNS), which is the brain and spinal cord. The vagus nerve, which controls the heart and the digestive tract, links the CNS to the digestive tract. So stimulation to the CNS will also affect digestion.

Additionally, caffeine contains colon-stimulating agents called theophylline and xanthine. They create contractions called “peristalsis.” This moves particles along the gut, making stool move closer to your rectum, and then suddenly you have that urgent bowel movement sensation.

Why does it happen so fast after the first sip?

People metabolize caffeine at totally different speeds, so this is totally subjective. But for many of us, it is our first beverage after waking. So that, coupled with your first meal (particularly if it’s fibrous), will encourage regularity.

Flickr/jaci XIII

Is it the coffee or the caffeine that does it?

The xanthine in coffee PLUS the amount of caffeine appear to be responsible for stimulating a bowel movement. Some of my patients report more bowel movements after drinking coffee, but not so much with other caffeinated beverages.

Is everyone equally sensitive to caffeine's laxative properties?

Some individuals may not even feel caffeine’s laxative effects, while others will react immediately. People with irritable bowel syndrome (IBS) or irritable bowel disease (IBD) are usually more sensitive and should be cautious when ingesting coffee and other caffeinated beverages. Caffeine can also exacerbate acid reflux, stomach ulcers, and other gastrointestinal conditions.

What other drinks have similar effects?

Strong caffeinated tea can have similar effects, as can hot cocoa and hot chocolate. However, energy drinks don’t appear to stimulate a bowel movement quite like coffee.

Does coffee cause you to pee too?

More evidence is needed to understand how caffeine affects your pee habits, but some research suggests that xanthine stimulates water diuresis (peeing after drinking water), in addition to the aforementioned peristalsis. But this may depend on the amount of caffeine ingested -- some studies indicate that the diuretic effects of caffeine are experienced only with amounts equal or greater to 250mg.

sitting on toilet

Is it healthy to drink coffee for this express purpose?

I don’t suggest an excessive intake of coffee (more than two 8oz cups per day) for the sole purpose of stimulating a bowel movement. An excessive caffeine intake (higher than 740mg) may excrete calcium and magnesium from your body, induce hypertension, and exacerbate anxiety. Excessive caffeine intake may also disrupt sleep, as it takes about 10 hours for caffeine to leave the body. Coffee can also make stools harder to pass -- it’s a diuretic, so it draws liquid out of stools.

Adequate consumption of dietary fiber, proper hydration, stress management, and daily exercise can help you have healthy, regular bowel movements. Check out this article for more tips on healthy digestion and maintaining a happy belly!

Do different brew methods make a difference? Will you poop more if you drink espresso as opposed to instant or drip?

Roasting, grinding, and brewing times can all affect the amount of caffeine. For example, one fluid ounce of espresso will have 50-75mg of caffeine, while 8oz of brewed coffee contains 95-200mg of caffeine.

Do additions like milk, cream, and/or sugar/sugar substitutes make a difference?

Generally speaking, the laxative and diuretic effects of caffeine are experienced with or without sugar, cream, or dairy and non-dairy milk. Some artificial sweeteners contain sugar alcohols, which may cause bloating and gastrointestinal discomfort, though. Milk and cream may also affect an individual if they are lactose intolerant, and additives like guar gum and carrageenan may have similar negative digestive effects.

Our managing editor Bison wonders why coffee makes him pee differently than other beverages. To quote: "Like, beer makes me have to pee, but it'll be a large volume maybe once per hour, whereas coffee makes me pee a little bit every 15 goddamn minutes."

Both alcohol and caffeine are diuretics but have different mechanisms for stimulating diuresis. Alcohol inhibits vasopressin -- an anti-diuretic hormone that is released from the pituitary gland. As a result, we will experience more urgency to urinate.

Jacqueline Aizen is a registered dietitian and graduate of New York University, where she pursued her interest in nutrition studies. She has written for Prevention, and is currently a contributor for Be Light Living, and a health expert for ChickRx.