Food intolerance

Also called Lactose intolerance, Food sensitivity, Non-allergic food hypersensitivity

Not an allergy, and the difference is life or death. Allergy involves the immune system and can kill; intolerance makes you feel unwell.

What it is

Difficulty digesting a food, causing symptoms that are unpleasant but not immune-mediated and not life-threatening.

**The distinction from allergy is the most important thing in this entry.** Allergy is an immune reaction, can involve hives, swelling and breathing difficulty, and can be fatal within minutes. Intolerance causes bloating, wind, diarrhoea or discomfort over hours, and does not cause anaphylaxis. Conflating them leads either to unnecessary fear or, far more dangerously, to a real allergy being dismissed as fussiness.

The commonest true intolerance is lactose intolerance, from reduced lactase enzyme. It is normal in most of the world's adults and is more common in people of African, Asian and Middle Eastern heritage. It is dose-related: most people can manage some lactose, and hard cheese and yoghurt are usually tolerated.

Other recognised patterns include sensitivity to fermentable carbohydrates in irritable bowel syndrome, reactions to sulphites, histamine and caffeine, and non-coeliac gluten sensitivity.

Before assuming intolerance, coeliac disease must be excluded, and the test only works while still eating gluten. Cutting gluten out before testing is the commonest reason coeliac disease is missed for years.

Commercial food intolerance tests, IgG blood tests, hair analysis and kinesiology, are not valid and lead to unnecessary and sometimes harmful restriction.

Signs you might notice

Bloating, wind, abdominal pain and rumbling.

Diarrhoea or loose stools, sometimes constipation.

Nausea, tiredness, headache after eating.

Symptoms coming on within a few hours and related to how much was eaten.

Not intolerance, and needing urgent attention: any swelling of the lips, tongue or throat; hives; wheeze or difficulty breathing; vomiting immediately after eating a specific food; or feeling faint. Those are allergy and can be an emergency.

Red flags needing investigation rather than a food diary: weight loss, blood in the stool, anaemia, vomiting, difficulty swallowing, a change in bowel habit over 50, or a family history of bowel disease.

How it can affect day-to-day life

Self-diagnosed intolerance is extremely common, and self-imposed restriction can cause real harm: inadequate calcium in dairy avoidance, missed coeliac disease, and in children, faltering growth and food fear.

For a child, restricting food groups without dietetic input is a genuine risk, and overlaps with ARFID in some cases.

The social cost is under-rated. Eating out, school meals, family occasions and workplace catering all become negotiations.

Lactose intolerance is manageable: lactase drops and tablets, lactose-free dairy, and building tolerance with small amounts spread through the day.

For IBS, a properly supervised low FODMAP diet works for many people and must be done with a dietitian, because it is restrictive, temporary, and has a structured reintroduction phase that people skip.

Supporting someone well

Rule out coeliac disease before removing gluten, and keep eating gluten until tested.

Learn the difference between allergy and intolerance, and never dismiss swelling, hives or breathing difficulty as intolerance.

Keep a food and symptom diary for two weeks rather than guessing.

Do not use commercial intolerance tests; they are not valid.

Eliminate one food properly for two to four weeks and then reintroduce it to confirm, rather than cutting out several at once.

Ask for a dietitian before restricting anything long term, and always for a child.

Replace what is removed: calcium and vitamin D if avoiding dairy.

Do the low FODMAP diet only with dietetic supervision, including the reintroduction phase.

Get the red flag symptoms investigated.

Where to get help

A GP practice for coeliac testing and for red flag symptoms.

A registered dietitian, through NHS referral or the British Dietetic Association directory.

An allergy clinic for suspected true allergy.

Guts UK and Coeliac UK for reliable information.