“Indigestion” refers to any number of gastrointestinal complaints, which can include gas (belching, flatulence, or bloating) and upset stomach.
“Heartburn” refers to a burning feeling that can be caused by stomach acid regurgitating into the esophagus from the stomach, by gastritis (inflammation of the lining of the stomach), or by an ulcer of the stomach or duodenum (also called peptic ulcer).
“Low stomach acidity” refers to the inability to produce adequate quantities of stomach acid that will affect digestion and absorption of nutrients.
In some cases, such as lactose intolerance, symptoms of indigestion are due to a specific cause that requires specific treatment. Sometimes symptoms associated with indigestion are caused by diseases unrelated to the gastrointestinal tract. For example, ovarian cancer may cause a sensation of bloating. Anyone with symptoms of indigestion should be properly diagnosed by a healthcare professional before assuming that the information below is applicable to their situation.
The most common cause of heartburn is gastroesophageal reflux disease (GERD), in which the sphincter between the esophagus and the stomach is not functioning properly. Another, related cause of heartburn is hiatal hernia, in which a small portion of the stomach protrudes through the aforementioned sphincter.