Acid reflux — when stomach acid travels back up into the oesophagus — is one of the most common digestive conditions globally. Most people think of it as a simple mechanical problem: a valve that is not closing properly. The gut microbiome connection makes the picture considerably more interesting.
What actually causes reflux
The lower oesophageal sphincter is a ring of muscle at the junction between your oesophagus and your stomach, acting as a one-way valve. Reflux happens when this valve relaxes when it should not. Several things contribute: carrying excess weight around the abdomen (which increases pressure on the stomach), eating large meals, lying down too soon after eating, pregnancy, and certain foods — fatty foods, chocolate, alcohol, coffee, and mint — that relax the valve.
When reflux is frequent enough to cause symptoms or actual tissue damage to the oesophagus, it is classified as GERD.
The microbiome connection
Bacterial overgrowth in the small intestine produces more gas than normal, increasing upward pressure in the gut and contributing to reflux. The gut microbiome also influences how quickly the stomach empties after a meal — a stomach that empties slowly stays fuller for longer, increasing the chance of contents travelling back up. Research has also found that the oesophagus itself has its own small bacterial community, and that community differs significantly in people with chronic GERD compared to those without it.
A note on long-term acid-suppressing medication
These medications are effective and sometimes medically necessary. Long-term use, however, removes stomach acid — one of the body's main defences against bacterial overgrowth. Studies have found that long-term users of these medications have measurably lower gut bacteria diversity. If you have been using acid-suppressing medication for more than a few months for mild reflux, it is worth discussing with your doctor whether a gradual reduction alongside lifestyle changes is appropriate.
Your next steps: If you use acid-suppressing medication regularly, discuss with your doctor whether long-term use is necessary for your situation, or whether a gradual reduction alongside dietary changes is worth exploring. Do not stop acid medication abruptly without guidance. In parallel, address the most modifiable factors this week: eat smaller evening meals, avoid eating within two hours of bed, and keep a symptom diary for two to three weeks to identify your personal food triggers. If overweight, even a modest weight loss meaningfully reduces reflux — it is one of the most evidence-backed interventions for this condition.
This content is for educational purposes only and is not a substitute for professional medical advice.