“Indigestion” refers to any number of gastrointestinal complaints, which can include wind (belching, flatulence, or bloating) and upset stomach. “Heartburn” refers to a burning feeling that can be caused by stomach acid regurgitating into the oesophagus 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 Gastro-oesophageal reflux disease (GERD), in which the sphincter between the oesophagus 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.

According to Jonathan Wright, MD, another cause of heartburn can be too little stomach acid.¹ This may seem to be a paradox, but based on the clinical experience of a few doctors such as Dr. Wright, supplementing with betaine HCl (a compound that contains hydrochloric acid) often relieves the symptoms of heartburn and improves digestion, at least in people who have hypochlorhydria (low stomach acid). The amount of betaine HCl used varies with the size of the meal and with the amount of protein ingested. Typical amounts recommended by doctors range from 600 to 2,400 mg per meal. Use of betaine HCl should be monitored by a doctor and should be considered only for indigestion sufferers who have been diagnosed with hypochlorhydria.

Medical researchers since the 1930s have been concerned about the consequences of hypochlorhydria. While all the health consequences are still not entirely clear, some have been well documented.

Many minerals and vitamins appear to require adequate concentrations of stomach acid to be absorbed optimally—examples are iron,²zinc,³ and B-complex vitamins,⁴ including folic acid.⁵ People with achlorhydria (no stomach acid) or hypochlorhydria may therefore be at risk of developing various nutritional deficiencies, which could presumably contribute to the development of a wide range of health problems.

One of the major functions of stomach acid is to initiate the digestion of large protein molecules. If this digestive function is not performed efficiently, incompletely digested protein fragments may be absorbed into the bloodstream. The absorption of these large molecules may contribute to the development of food allergies and immunological disorders.^{6, 7}

In addition, stomach acid normally provides a barrier against bacteria, fungi, and other organisms that are present in food and water. People with inadequate stomach acidity may therefore be at risk of having “unfriendly” microorganisms colonize their intestinal tract.^{8, 9} Some of these organisms produce toxic substances that can be absorbed by the body.

Some researchers have found that people with certain diseases are more likely to have an inability to produce normal quantities of stomach acid. However, this does not mean these diseases are caused by too little stomach acid. Jonathan Wright, MD, usually tests patients’ stomach acid if they suffer from food allergies, arthritis (both rheumatoid arthritis and osteoarthritis), pernicious anaemia (too little vitamin B12), asthma, diabetes, vitiligo, eczema, trigeminal neuralgia, Addison’s disease, coeliac disease, lupus erythematosus, or thyroid disease.¹⁰