Coffee does make you poop, but it's not because of caffeine

• Coffee does promote bowel movements, though doctors are unsure exactly why this happens.
• Caffeine is not why coffee makes some people poop since decaf coffee can have the same effect.
• Four cups of coffee is the maximum recommended amount you should drink in a day.

For many people, a day doesn't start unless they've had their cup of coffee, but this morning staple is often followed by a trip to the bathroom. In a small 1990 study, coffee stimulated a bowel movement in 29% of participants. However, there's no definite answer on what it is about coffee that causes a laxative effect.

Most people think caffeine is to blame. Though caffeine is shown to cause an earlier urge to have defecate and is a known stimulant, decaffeinated coffee can stimulate bowel movements as well.

"It must be something about coffee as a whole, rather than the caffeine in isolation, that stimulates a bowel movement," says Jill Deutsch, MD, director of the Yale Functional Gastrointestinal Disorders Program.

Here's what you need to know about the laxative effects of drinking coffee.

Why does coffee make you poop?

The exact reason for coffee's laxative effect is unclear, but doctors assume it's a combination of factors. "The short answer is that we aren't quite sure! It seems just to be the overall formulation of coffee that helps us poop," says Deutsch.

How coffee effects your bowels:

• Milk: Drinking milk can cause bloating, increased gas, and diarrhea to people with lactose intolerance, the inability to digest the sugar found in dairy. They may benefit from choosing lactose-free milk options such as soy, oat, coconut, and almond milk.
• Gastrin levels: Both caffeinated and decaffeinated coffee can increase gastrin levels, the hormone that makes the colon more active.
• Motor function of the colon: With or without caffeine, coffee can stimulate the motor activity of the colon, or the contractions that cause the urge to have a bowel movement.
• Timing: Colonic motor activity naturally increases after waking up, which might explain why some people feel like going to the bathroom in the morning.

There's no specific amount of coffee that will stimulate a bowel movement because it's different for everyone. "Not everyone derives the same sort of laxative benefit from drinking coffee. And in fact some people aren't affected at all by drinking coffee," says Deutsch.

Is it healthy to drink coffee as a laxative?

If it works for you, it may be healthy to drink coffee as a laxative, says Deutsch. Consuming up to 400 milligrams of caffeine daily is safe without adverse effects, which is roughly the amount in four cups of coffee. However, sustained consumption of higher doses may lead to caffeine dependence.

What the research says: According to a 2013 study, caffeine is the most widely used drug in the world. It's important to consume less than 400 milligrams of caffeine daily to avoid symptoms of caffeine dependence such as a strong desire to keep consuming the drug, difficulties in controlling your drug consumption, and withdrawal.

Other beverages contain caffeine as well, such as sodas, teas (including kombucha), and energy drinks. However, there's no research proving that they provide a similar laxative effect to that of coffee. "We don't have data to support that other caffeinated beverages stimulate a bowel movement," says Deutsch.

Insider's takeaway

Caffeinated and decaffeinated coffee stimulate bowel movement for some people, but there's no solid reason why that is. The overall digestive effects of coffee, milk, and the time you drink it may all contribute to the laxative effect.

It can be healthy to drink coffee as a laxative if it works for you, but a sustained consumption of more than 400 milligrams of caffeine in a day (which is about cups of coffee) may lead to caffeine dependence. Keep in mind that caffeine is not only found in coffee, but also in teas, sodas, and energy drinks as well, though they are not proven to stimulate bowel movement.

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