What is the cause?
Reflux and heartburn are caused by the acid contents of the stomach regurgitating or flowing backwards into the oesophagus. The lining of the oesophagus is not designed to handle these high acid conditions, which leads to inflammation and in severe cases scarring of the oesophagus. This is called oesophagitis. Chronic inflammation of the oesophagus can lead to a type of scarring called Barrett’s oesophagus. This has a chance of progressing into oesophageal cancer.
The stomach produces a lot of hydrochloric acid during eating and for good reason, because without it, you cannot digest proteins efficiently and you will not absorb calcium and other minerals from foods. There is a circular muscle around the lower oesophagus, which divides it from the stomach, and this normally remains contracted to prevent back flow of stomach acid. During swallowing, this muscle normally relaxes, allowing food to pass from the oesophagus into the stomach, after which it should remain contracted.
If you are overweight and/or have a fatty liver, this will cause too much pressure on the stomach, and reflux becomes worse. If you eat a lot of sugar or refined carbohydrates, or you have problems digesting FODMAPs, you may develop small intestinal bacterial overgrowth. Gases the bacteria produce can travel up into the stomach, raising the pressure inside and promoting reflux. Food intolerance can also increase gas production in the gut.
In some people with reflux there is a hernia (protrusion) of the upper part of the stomach through the diaphragm into the lower chest. This is called a hiatus hernia and can be hereditary and is more common with age and in those who are overweight. A hiatus hernia will often disturb the function of the circular muscle around the lower oesophagus. This increases reflux and heartburn symptoms. These symptoms are much worse after eating a large meal and while bending over.