Hypochlorhydria and Pancreatic Insufficiency: Overlooked Drivers of Digestive Symptoms

Digestion is often discussed as if it began in the small intestine, where most nutrients are absorbed, or in the colon, home of the microbiome. In fact, 2 organs upstream do much of the chemical work: the stomach, which secretes acid and pepsin, and the pancreas, which supplies the enzymes that break down fat, protein and carbohydrate. When either underperforms, the consequences ripple downstream, producing symptoms and deficiencies that are often attributed to something else. Both conditions are common in certain groups, both are frequently missed, and both are treatable.

Part one: hypochlorhydria

What stomach acid does

• Protein digestion: acid activates pepsin and unfolds proteins.
• Nutrient absorption: acid releases vitamin B12 from food proteins, converts dietary iron into its more absorbable form, and aids absorption of calcium from some supplements, particularly calcium carbonate.
• Defence: acid kills many swallowed microorganisms, protecting the small intestine from colonisation and infection.
• Signalling: gastric acidity influences the release of hormones that coordinate downstream digestion.

Causes of low acid

Consequences

The main consequences are nutritional and infectious. Vitamin B12 and iron deficiency are the most important. Long term acid suppression has also been associated with increased risk of enteric infections, including Clostridioides difficile, and with low magnesium, although some associations in observational studies may reflect the characteristics of people who take these medicines. Low acid may contribute to small intestinal bacterial overgrowth. Autoimmune atrophic gastritis carries an increased risk of gastric neuroendocrine tumours and gastric cancer, which is why it may need endoscopic surveillance.

The symptom paradox

Low stomach acid is sometimes said to cause reflux, bloating and indigestion that are then mistakenly treated with more acid suppression. The evidence for this idea is limited. Reflux is primarily a problem of the lower oesophageal sphincter and gastric motility rather than of acid quantity, and acid suppression is effective and important for erosive oesophagitis, peptic ulcer disease and other conditions. The more useful clinical point is that symptoms of indigestion have many causes, and not all require acid suppression indefinitely.

Assessment

Validated approaches include testing for Helicobacter pylori; blood tests such as gastrin, which rises when acid is low, and pepsinogen levels and ratios, which fall in atrophic gastritis; parietal cell and intrinsic factor antibodies for autoimmune gastritis; and endoscopy with biopsy for definitive diagnosis. Home tests, such as drinking baking soda and timing belching, and challenge protocols with betaine hydrochloride capsules have no validated diagnostic value.

Management

• Treat Helicobacter pylori infection where present.
• Replace B12 and iron as needed.
• Review long term acid suppression. Deprescribing guidance supports trying to reduce or stop proton pump inhibitors in adults treated for reflux or dyspepsia whose symptoms have resolved, while continuing them where there is a clear ongoing indication, such as Barrett oesophagus, severe oesophagitis, a history of bleeding ulcers or ongoing high risk medication use. Tapering helps avoid rebound symptoms.
• Arrange surveillance where recommended for atrophic gastritis.
• Be cautious with betaine hydrochloride supplements. Evidence of benefit is minimal, and they are inappropriate in people with ulcers, gastritis or those taking anti inflammatory drugs or steroids.

Part 2: exocrine pancreatic insufficiency

What the pancreas does

The exocrine pancreas secretes lipase, which digests fat; proteases, which digest protein; and amylase, which digests starch, along with bicarbonate that neutralises stomach acid. Lipase is the most critical, because there is little backup for fat digestion elsewhere in the gut.

Causes

Symptoms and signs

Classic features include steatorrhoea, pale, bulky, greasy, foul smelling stools that are difficult to flush; bloating and flatulence; abdominal discomfort after meals; and weight loss. Deficiencies of fat soluble vitamins A, D, E and K can develop, with consequences for bone health, vision, neurological function and blood clotting. Milder insufficiency may produce only bloating and loose stools, and is easily mistaken for irritable bowel syndrome.

Diagnosis

Faecal elastase, measured in a formed stool sample, is the most widely used test. Levels below 200 micrograms per gram suggest insufficiency, and below 100 indicate more severe insufficiency. Watery stool can falsely lower the result by dilution. Imaging may identify pancreatic disease, and assessment for an underlying cause is essential, particularly in older adults presenting for the first time.

Treatment

Pancreatic enzyme replacement therapy is the mainstay. Its effectiveness depends on correct use:

• enzymes must be taken with meals and snacks, not before or after;
• doses are based on lipase units and adjusted to fat intake and response, with starting doses per main meal recommended in European guidelines;
• acid suppression is sometimes added to improve enzyme activity if response is inadequate;
• fat soluble vitamins are monitored and replaced;
• a normal fat intake is usually encouraged rather than restricted, as enzymes allow fat to be digested.

Over the counter digestive enzyme supplements are not equivalent to prescription pancreatic enzymes in dose, formulation or evidence, and should not replace them in diagnosed insufficiency.

Recognising both in practice

Consider these conditions when a patient has:

• unexplained B12 or iron deficiency;
• fatty, pale or floating stools, or weight loss with digestive symptoms;
• deficiency of vitamin D or other fat soluble vitamins despite adequate intake;
• bloating and loose stools with risk factors such as diabetes, previous pancreatitis, gut surgery or long term acid suppression;
• new digestive symptoms and weight loss in later life, which require prompt medical assessment.

An illustrative case

A 66 year old man with type 2 diabetes and a history of heavy drinking, now abstinent, has had loose, pale, greasy stools, bloating and 6 kg of weight loss over a year. He has been told he has irritable bowel syndrome and has reduced his fat intake, which helped slightly. His vitamin D is low despite supplementation. His doctor orders a faecal elastase, which is below 100 micrograms per gram, and arranges imaging, which shows changes of chronic pancreatitis and no mass. He starts pancreatic enzyme replacement with meals, his vitamin D is replaced at a higher dose, and he is encouraged to return to a normal diet. His stools normalise, his weight stabilises, and his diabetes control improves as his nutrition improves.

Looking upstream

When digestive symptoms, malabsorption or deficiencies are unexplained, it is worth looking upstream. The stomach and pancreas are easily overlooked in assessments focused on the microbiome and the small intestine, yet their failure produces some of the most treatable problems in digestive medicine.