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Coffee is one of the most popular beverages in the world.

It can not only make you feel more alert but also potentially offer many other benefits, including improved mood, mental performance, and exercise performance, as well as a lower risk of heart disease and Alzheimer’s (1, 2, 3, 4).

However, some people find that drinking coffee affects their digestive system.

This article explores the reasons why coffee may upset your stomach.

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Compounds that may upset your stomach

Coffee contains various compounds that may upset your stomach.

Caffeine

Caffeine is a natural stimulant in coffee that helps you stay alert.

A single 8-ounce (240-mL) cup of coffee contains approximately 95 mg of caffeine (5).

Though caffeine is a potent mental stimulant, research suggests that it can increase the frequency of contractions throughout your digestive tract (6, 7, 8).

For example, an older study from 1998 found that caffeinated coffee stimulates the colon 23% more than decaf coffee, and 60% more than water. This indicates that caffeine significantly stimulates your lower gut (9).

Also, some research suggests that caffeine may increase the production of stomach acid, which could upset your stomach if it’s especially sensitive (10).

Coffee acids

While caffeine is often viewed as the reason why coffee may cause stomach issues, studies have shown that coffee acids may also play a role.

Coffee contains many acids, such as chlorogenic acid and N-alkanoyl-5-hydroxytryptamide, which have been shown to increase stomach acid production. Stomach acid helps break down food so it can move through your gut (11, 12).

That said, while some people have reported that coffee may aggravate heartburn symptoms, research is inconclusive and shows no significant connection (13, 14).

Other additives

In some cases, the coffee isn’t what makes your stomach upset.

In fact, stomach upset could be due to additives like milk, cream, sweeteners, or sugar, which more than two-thirds of Americans add to their coffee (15)

For example, approximately 65% of people worldwide cannot properly digest lactose, a sugar in milk, which may trigger symptoms like bloating, stomach cramps, or diarrhea soon after consuming dairy (16).

Coffee has several compounds that may upset your stomach, such as caffeine and coffee acids. Plus, common additives like milk, cream, sugar, or sweeteners may upset your stomach as well.

Can decaf coffee upset your stomach?

In some instances, switching to decaf may help with an upset stomach.

This mainly applies if caffeine is the culprit of your stomach issues.

That said, decaf coffee still contains coffee acids, such as chlorogenic acid and N-alkanoyl-5-hydroxytryptamide, which have been linked to increased stomach acid production and gut contractions (11, 12).

Moreover, adding milk, cream, sugar, or sweeteners to decaf coffee may cause stomach issues in individuals who are sensitive to these additives.

Despite being free of caffeine, decaf coffee still contains coffee acids and possibly additives, which could upset your stomach.

Tips to avoid an upset stomach

If you find that coffee upsets your stomach, several things can reduce its effects so you can enjoy your cup of joe.

For starters, drinking coffee slowly in sips may make it easier on your stomach.

Also, try to avoid drinking coffee on an empty stomach. Coffee is considered acidic, so sipping it alongside food could ease its digestion.

Here are several other ways to minimize coffee’s acidity:

• Choose a darker roast. A study found that coffee beans that were roasted longer and at higher temperatures were less acidic, which means darker roasts tend to be less acidic than lighter roasts (17).
• Try cold-brewed coffee. Research suggests that cold-brewed coffee is less acidic than hot coffee (18, 19).
• Choose larger coffee grounds. One study found that smaller grounds of coffee may allow for more acid to be extracted during brewing. This means that coffee made from larger grounds may be less acidic (19).

Moreover, if you enjoy your cup of coffee with milk but are lactose intolerant or feel that milk upsets your stomach, try switching to a plant-based milk alternative, such as soy or almond milk.

If you find that coffee upsets your stomach, try a few of the tips above. In many cases, reducing the acidity of coffee or avoiding additives may help combat coffee-related stomach issues.

The bottom line

Coffee has several compounds that may upset your stomach.

This includes caffeine, coffee acids, and often other additives, such as milk, cream, sugar, and sweeteners. Apart from caffeine, many of these compounds are also present in decaf coffee.

If you find that coffee upsets your stomach, there are several things you can do to minimize its unpleasant effects. These include drinking it with food, choosing a lower acidic roast, switching from regular milk to soy or almond milk, and cutting back on additives.