Food intolerance
A reaction of the digestive system to a food that does not involve the immune system, usually resulting from an inability to digest the substance properly (enzyme deficiency or malabsorption).
Unlike an allergy, an intolerance does not activate the immune system and does not produce IgE. Symptoms are digestive and delayed (a few hours to 2 days after eating): bloating, wind, diarrhoea, constipation and abdominal pain.
Main causes:
- Lactose intolerance: lactase deficiency (the enzyme that digests lactose). Affects about 75% of the world’s population (more so among people not of northern European descent)
- Fructose intolerance: malabsorption of fructose (the sugar in fruit and honey). Often confused with IBS
- FODMAPs: fermentable sugars that cause bloating (see FODMAP)
- Dietary histamine: build-up in people with a DAO deficiency (the enzyme that breaks down histamine)
A fresh angle: intolerances are reversible. They can resolve by restoring gut flora and temporarily removing the trigger food. Lactose intolerance can lessen by gradually reintroducing dairy (the gut increases its lactase production). Dysbiosis caused by antibiotics or chronic inflammation can secondarily generate intolerances to lactose, fructose or FODMAPs, and putting the gut right resolves them.
Diagnosis is by gradual elimination, not a blood test (unlike allergies).