Food Intolerance
A reproducible adverse reaction to a food that does not involve the immune system.
Last revised
Key takeaways
- Not the same as allergy: intolerance does not involve IgE or anaphylaxis
- Commonest example: lactose intolerance
- Most useful single change: Keep a detailed food and symptom diary before excluding anything.
- Commonest mistake: Commercial IgG or hair-analysis food tests.
- See a doctor if any of the signs under "When to get help" below apply to you.
Why it matters
It is frequently confused with allergy, which is a different mechanism with a different level of danger, and with tests that do not work.
The numbers, in one place
| Measure | Figure |
|---|---|
| Not the same as allergy | intolerance does not involve IgE or anaphylaxis |
| Commonest example | lactose intolerance |
| Onset | usually gradual and dose-related |
| IgG food tests | not recommended; they do not diagnose intolerance |
| Diagnosis | structured exclusion and reintroduction, ideally with a dietitian |
What helps
- Keep a detailed food and symptom diary before excluding anything
- Exclude and then reintroduce systematically to confirm
- Ask for dietitian support for any exclusion lasting more than a few weeks
- Test for coeliac disease before removing gluten
What to avoid
- Commercial IgG or hair-analysis food tests
- Long-term exclusion of whole food groups without advice
- Confusing intolerance with allergy when describing symptoms to clinicians
Where to go next
- Myths About Food Intolerance, Checked Against the Guidance
- Starting Out With Food Intolerance
- What the Guidance Really Says About Probiotics
- The Evidence on Liver Health, Without the Hype
When to get help
Call 999 for swelling of the lips, tongue or throat, difficulty breathing or swallowing, a widespread rash with faintness, or collapse after eating — that is anaphylaxis, not intolerance, and needs adrenaline immediately. See a GP for persistent diarrhoea, weight loss or blood in the stool rather than assuming intolerance.
Where this comes from
- NICE — Food allergy in under 19s
- British Dietetic Association — food allergy and intolerance
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarised or generalised beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to a GP, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 999.