Over the years, there has been extensive research into the health benefits of coffee. Medical experts and nutritionists alike agree that coffee’s high antioxidant content can prolong life expectancy and reduce the risk of certain diseases, as well as other benefits.

However, it’s also proven that consuming high levels of caffeine can result in adverse side effects. These can include an increased heart rate, restlessness, headaches, and stomach problems.

Considering the latter, which compounds in coffee can result in digestive issues? And are there any ways to prevent these problems occurring?

To find out more, I spoke with three coffee researchers. Read on to find out what they had to say. 

You may also like our article on coffee, health, and wellness.

Which compounds in coffee can cause stomach issues?

When consumed in larger quantities, there are several compounds in coffee which can cause stomach problems. One of the most prominent is caffeine.

Caffeine is a natural stimulant which is found in coffee, tea, cocoa, and yerba maté, as well as in other food and beverage ingredients. It helps to stimulate the brain and central nervous system, and can also help to reduce fatigue and tiredness. It does this by blocking the effects of adenosine, which is a neurotransmitter that makes us feel tired.

However, alongside its positive effects, high levels of caffeine consumption can also have adverse effects on human health.

Verônica Belchior is a coffee consultant and Q-grader. She also has a PhD in Food Science.

She explains that because caffeine’s biggest effect is on the brain, it is technically a psychoactive substance.

“When consuming low doses, such as 50mg, caffeine can reduce anxiety,” she says. “High doses (between 150mg and 450mg), meanwhile, can increase anxiety, nervousness, and jitteriness.”

Verônica adds that because caffeine is a psychoactive substance, the body can become physiologically dependent on it if consumed on a regular basis.

“If you drink coffee every day, and then abruptly reduce your consumption, you could experience several withdrawal symptoms,” she explains. “These can include higher levels of fatigue or drowsiness, lower levels of alertness, reduced concentration, mood swings, and headaches – as well as nausea or stomach issues.”

When it comes to caffeine intake and digestive problems, a study from 1998 found that caffeinated coffee stimulated the colon 23% more than decaf coffee. 

Moreover, further research concludes that consuming more caffeine can increase the production of stomach acid. Ultimately, in large amounts, this can trigger stomach issues – especially for those who are more sensitive to caffeine.

What about other compounds?

As well as caffeine, there are a number of other compounds in coffee which can result in digestive problems.

“Low pH levels of coffee can be a problem for those who are susceptible to gastritis,” says Verônica. Gastritis is when the lining of the stomach becomes inflamed and irritated, which can cause indigestion and nausea. 

Sebastian Opitz is the Head of Green Coffee at the Coffee Excellence Centre at the Zurich University of Applied Sciences. 

“The relationship between coffee and stomach problems is often more complex than we think,” he tells me. “In our research on this topic, we have mostly studied the chemical composition of green coffee.

“The focus of our research was on a particular part of lipids found in green coffee called tryptamides, or alkanoyl tryptamides,” he adds. “These are found on the waxy, outside layer of green coffee beans, and they can increase the secretion of gastric acid in the stomach.”

Moreover, Sebastian tells me that other compounds found in green coffee, such as catechol and pyrogallol (which result in bitter flavours), can also increase gastric acid secretion. However, Sebastian points out that because these two compounds are only present in green coffee in small quantities, their impact on stomach health is most likely minimal.

There is also conflicting research on the relationship between compounds such as chlorogenic acids and trigonelline and the secretion of gastric acid. While some studies claim these compounds increase the secretion of gastric acid, other research states that secretion decreases.

Are certain demographics more susceptible?

Chahan Yeretzian is the Head of the Coffee Excellence Centre. He explains that the majority of people who have stomach issues when drinking coffee report experiencing gastric reflux, which is also known as heartburn. This is when stomach acid moves into the oesophagus, which often results in a burning sensation in the chest.

However, Chahan tells me that there is little evidence exploring how coffee consumption causes gastric reflux.

“Stomach issues caused by drinking coffee aren’t related to any particular cultural or ethnic group, as well as age or gender,” he explains. “We also don’t know the proportion of people affected.

“The likelihood of experiencing stomach problems from drinking coffee is largely based on individual differences, but it could also be genetic, although there currently isn’t enough evidence to support this claim,” he adds. 

Do some coffees cause stomach issues more than others?

Although most green coffee contains the same compounds, there are a number of ways that its chemical composition can change. This includes different sensory profiles, processing methods, roast levels, brewing methods, and more.

Sensory profile

Every coffee has its own unique sensory and flavour profile. For example, some coffees have more bitter-tasting compounds or more pronounced acidity.

Chahan explains that in addition to bitter taste receptors in the mouth, they are also found in the stomach and other organs, such as the gallbladder.

“A study from 2017 showed that when bitter taste receptors in the stomach sensed caffeine (a bitter-tasting compound), secretion of gastric acid increased rapidly,” Sebastian says. “This helps to explain the link between bitter-tasting compounds and toxicity. 

“Toxic compounds taste bitter, so when the stomach senses bitterness from caffeine, it wants to remove it,” he adds. “The quick release of gastric acid helps to decompose the ‘toxic substance’ before it can do any harm to the body.”

When it comes to acidity, there seems to be less of a causal link.

“Some people say that acidity in coffee increases acidity in the body, and therefore acidic-tasting coffee isn’t good for you,” Sebastian says. “However, this explanation is not correct.

“There’s a correlation, but not a causality, between the two,” he adds. “Even though coffee is acidic, it generally has a pH level of five, while the pH level of gastric acid in the stomach is below two.”

In essence, this means acid in the stomach is minimally affected by the acidity in coffee.

“People sometimes claim that when experiencing heartburn after drinking coffee, it’s because of the coffee’s acidity,” Sebastian tells me. “However, several compounds in coffee lead to an increase in the secretion of gastric acid in the stomach.

“In a 2010 study, researchers were able to identify these compounds,” he adds. “Moreover, if there is a higher secretion of acids, then the pH level in your stomach is lower, which can potentially lead to heartburn.”

Roast profile

The process of roasting not only has an irreversible impact on the cell structure of coffee beans, but also their chemical composition.

“Generally speaking, green coffee has the highest amount of chlorogenic acids,” Sebastian says. “Roasted coffee, meanwhile, contains around half of that in green coffee.”

Sebastian explains that roast profile also affects other compounds in coffee which can contribute to stomach problems.

“In simple terms, it’s better to drink darker roasted coffee than light roast,” he says. “The roasting process affects the coffee’s tryptamides levels, so the darker the roast level, the less tryptamides there will be in the beans.”

Ultimately, this means that the secretion of gastric acid won’t increase when drinking darker roasts, which can potentially mitigate any stomach issues.

“However, roasting to darker profiles tends to result in more bitter-tasting compounds, such as lindanes and chlorogenic lactones,” he adds. “But more research is needed to find out whether these compounds can trigger secretions of gastric acid.”

Brewing method

Sebastian explains that the brewing process can have a significant impact on the number of tryptamides in coffee.

“Espresso and French press both tend to extract higher concentrations of tryptamides,” Sebastian says. “Meanwhile, tryptamide concentrations in filter coffee are usually quite low because they are absorbed by the paper filter.

“However, tryptamides are only some of the compounds which contribute to the increased secretion of gastric acid,” he adds. “In our research, we are also analysing the effect of chlorogenic acids [on the stomach], but more evidence needs to be gathered.”

Processing method

It’s well known that processing methods have a significant impact on coffee flavour and quality. However, they also affect the chemical composition of green coffee.

“Natural processed coffees tend to have the highest concentration of tryptamides,” Sebastian says. “When analysing Monsoon Malabar and wet-hulled coffee, the concentrations become lower.

“We need to conduct further research, but it’s possible that longer fermentation times could decrease the concentration of tryptamides found in coffee,” he adds. “This is because the outer waxy layer is in contact with its environment for longer.”

What about decaf coffee?

It’s clear that caffeine, along with a number of other compounds in coffee, can cause stomach problems for some people. So is decaf less likely to trigger them?

“Decaf coffee can be a good solution for people who are sensitive to caffeine,” Verônica says. “However, the impact of caffeine consumption also depends on age, weight, and health conditions.”

According to Sebastian, the type of decaffeination process can also change the chemical composition of green coffee.

“We compared the effects of the carbon dioxide (CO2), the chloromethane, and the Swiss Water processes,” he tells me. “We found that the ‘milder’ processes, like the CO2 process, were able to remove almost all of the caffeine content without dissolving too many of the other compounds in green coffee.

“With the CO2 process, the beans were slightly darker, but they still had a green hue which you expect with green coffee,” he adds. “However, with the chloromethane and Swiss Water processes, the beans were more blotchy and brown coloured, so it’s clear that these processes alter the outer layer of the green coffee more.

“In turn, this could reduce the concentration of tryptamides in green coffee,” he continues. Ultimately, this could mean that decaf coffee is less likely to cause stomach issues compared to caffeinated coffee.

Should roasters be marketing “stomach-friendly” coffee?

Despite research indicating that certain compounds in coffee can cause stomach issues, Chahan says there isn’t enough consumer demand for “stomach-friendly” coffee.

“For instance, the world’s largest coffee companies are yet to market a ‘stomach-friendly’ coffee,” he says. “This clearly indicates that they don’t believe there is enough evidence for them to do so, although this could change soon.”

Sebastian mentions that low-caffeine varieties, such as Laurina and Aramosa, could also be an option for coffee drinkers who are more sensitive to caffeine.

“Looking at other coffee varieties and species which have lower caffeine concentrations could be helpful,” he concludes.

To summarise, there are certainly compounds in coffee which can cause stomach problems. However, this largely depends on a number of factors – including how much coffee you drink and how sensitive you are individually.

Although it can vary from person to person, moderate consumption of coffee is not likely to cause any stomach issues. 

Ultimately, by taking a more mindful approach to when and how often you drink coffee, you can reduce the likelihood of any potential stomach problems.

Enjoyed this? Then read our article on the relationship between oils in coffee & cholesterol levels.

Perfect Daily Grind

Disclaimer: we are not a medical publication. No material in this article is intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek medical advice from a qualified healthcare professional.

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