Is coffee bad for your stomach?

Coffee stimulates gastric acid secretion and slightly relaxes the lower oesophageal sphincter: in people prone to reflux or gastritis it can worsen symptoms. For everyone else, moderate intake (< 400 mg/day of caffeine) is not associated with gastric lesions, according to recent systematic reviews (Clinical Gastroenterology and Hepatology, 2020).

Two mechanisms explain coffee's bad reputation with sensitive stomachs. First, caffeine and several coffee compounds (N-alkanoyl-5-hydroxytryptamides, chlorogenic acids) stimulate hydrochloric acid production by the stomach's parietal cells. Second, caffeine reduces the tone of the lower oesophageal sphincter (LOS), the anatomical barrier that stops gastro-oesophageal reflux (GORD). For a healthy adult, both effects stay under the radar. For someone with GORD, gastritis, an ulcer or IBS, they can trigger heartburn, nausea or epigastric discomfort.

The acidity you taste in coffee is not your stomach's problem. A filter coffee has a pH between 4.85 and 5.10 on average — less acidic than orange juice (pH 3.5) or cola (pH 2.5). What irritates is not the liquid's acidity but the gastric stimulation it triggers. Several levers moderate the effect. Darker roasts contain fewer chlorogenic acids (destroyed during Maillard reactions), softening the stimulus. Cold brew, steeped 12-18 h in cold water, extracts 60-70 % less chlorogenic acids than espresso, and many reflux-prone drinkers tolerate it better (Thomas Jefferson University, 2018). A splash of milk also neutralises some acids.

Other digestive effects of coffee are neutral or even positive. Coffee accelerates colonic motility and can trigger the gastro-colic reflex within 4-30 minutes — the reason many Belgians credit the morning cup with 'laxative virtue'. Meta-analyses in BMJ and Gut (Kennedy et al., 2017) have even linked moderate coffee consumption to a reduced risk of gallstones (-25 % at 3 cups/day) and of several chronic liver diseases. In healthy drinkers, the notion that 'coffee damages the stomach' does not hold up against the data.

Seven practical tips for a sensitive stomach. Avoid coffee on an empty stomach (the gastric effect is maximal); choose a medium roast rather than an acid-bright light roast; try cold brew; pair with a snack (speculoos biscuit, tartine); skip syrups and sugary add-ons that worsen symptoms; cap at 2-3 cups/day; and if you are on proton-pump inhibitors or have an H. pylori infection, ask your gastroenterologist. This FAQ is informational; for any persistent symptom (burning, pain, nausea), a healthcare professional is the right contact.

Coffee and the stomach: what the data say