Can the Acid in Coffee Upset Your Stomach? Here’s What Gastroenterologists Want You To Know

If you’re a regular coffee drinker, you’re likely familiar with the way a cup of joe can keep you, well, regular. The coffee-to-bathroom pipeline is mostly the result of caffeine and other coffee compounds revving up gut motility, particularly increasing colon movement. That can lead to a strong urge to poop within minutes of finishing a cup, especially if it’s the first thing you’re drinking in the morning. But the effects of coffee on the gastrointestinal system don’t stop there—and both caffeinated and decaffeinated varieties can stir up some stomach discomfort (or trigger an existing stomach issue) in a couple of ways.

Perhaps the most widely touted cause of coffee-related stomach trouble is its acid content. But while it’s indeed rich in chlorogenic acids (aka natural polyphenols with strong antioxidant powers), as evidenced by the tang in its taste, these acids themselves aren’t usually the main instigator of stomach pain. The culprit? That would be the way certain coffee compounds can boost the stomach’s own acid production.

“Coffee can stimulate the stomach’s production of gastrin, which is the main hormone that acts on the parietal cells in the stomach to turn on their acid pumps.” —Scott Gabbard, MD, gastroenterologist

The stomach has a pH level of around 2 or lower, “which is highly acidic, whereas the pH of coffee is around 5, so that’s still acidic but much weaker than stomach juice and not likely to cause any direct effect,” says gastroenterologist Scott Gabbard, MD. “What can happen, though, is that the coffee can stimulate the stomach’s production of gastrin, which is the main hormone that acts on the parietal cells in the stomach to turn on their acid pumps.” The result is a more acidic stomach environment for up to 90 minutes after drinking that coffee, which can contribute to a stomachache, indigestion, or heartburn.

How different types and brews of coffee may cause stomach pain

While caffeine and chlorogenic acids are highly prevalent in your caffeinated morning brew, coffee can contain more than 800 different volatile compounds, all of which can affect people differently, says gastroenterologist Marvin Singh, MD. As a result, the science isn’t wholly conclusive on exactly which components of coffee can cause dyspepsia (aka sour stomach), though many people do note GI symptoms after drinking it, he says.

Part of that could certainly be tied to the digestion-stimulating effect of caffeine, which can push things through the GI system so speedily as to lead to abdominal cramping and diarrhea, particularly in people with irritable bowel syndrome. But if your discomfort post-coffee is more directly in your stomach or occurs even with decaf, it’s likely the result of particular coffee compounds triggering the stomach to release more of its own acid, as noted above. And some people are hyper-sensitive to that sensation, while others may not feel it at all, says gastroenterologist Lisa Ganjhu, DO, adding that coffee may also promote acid reflux by relaxing the lower esophageal sphincter and allowing stomach contents, acid and all, to more easily float back up.

Because of their natural variations in stomach-affecting compounds, all types and brews of coffees don’t necessarily have the same effects on the stomach, either. Notably, darker roasts tend to be a low-acid coffee option. “because the roasting process breaks down the phytochemicals and acidity of the beans themselves,” says Dr. Ganjhu. To that point, a 2010 study found that darker roasts also contain up to twice the amount of N-methylpyridinium (NMP), a compound that seems to block the ability of stomach cells to produce acid. And as a result, these blends are likely a better choice for anyone managing stomach irritation after a cuppa joe.

From there, every variable, from the type of bean to the place where the bean is grown, the grind size you choose, and the temperature at which you brew it, can affect the final acidity of your coffee—and potentially, the way it impacts the state of your stomach. “For example, Arabica beans grown at higher elevations will exhibit more acidity, while Robusta beans used for espresso tend to have lower acidity,” says Maryna Gray, director of coffee at coffee-subscription company Bean Box. “And cold-brewed coffee has also been shown to contain less acid than hot-brewed coffee because it’s suspected that hot extraction pulls out different compounds than cold.” Not to mention, adding milk to your coffee can also tamp down its overall acidity level, she adds.

A handful of brands, like Trücup and Euromild, are also producing lower-acid coffee blends, primarily by removing the waxy outer coating of the coffee beans with a pressurized steam treatment. Doing so strips away much of the chlorogenic acid content along with another kind of fatty acid compound that could be related to the stomach’s gastrin secretion. Additionally, other brands, like Volcanica and Simpatico, are focused on bagging naturally lower-acid varieties sourced from lower-altitude regions in Mexico and Central America.

Even so, there isn’t conclusive research to show that these low-acid coffee varietals (or any of the above variations in coffee-acid content) will necessarily spare you from stomach issues, if coffee seems to trigger them. Again, that’s more likely the result of your stomach’s own acid-producing response to the coffee—which could happen with a high- or low-acid cup. Still, there’s no harm in switching things up if your current brew isn’t cutting it, says Dr. Singh: “It’s possible that any number of unique characteristics of the beverage you drink can have an effect on the stomach’s production of acid and any symptoms you might have as a result.”

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