Could My Symptoms Be a Food Intolerance?

If certain foods leave you feeling unwell, it is natural to wonder whether you are reacting to something in your diet. But "food allergy" and "food intolerance" are often used interchangeably when they are actually very different things. Understanding the distinction matters, because it shapes which test is useful — and which are not.

Allergy versus intolerance

The two involve completely different mechanisms in the body:

• Food allergy — an immune reaction driven by IgE antibodies. It tends to come on quickly, within minutes to a couple of hours, and can cause hives, swelling, wheezing and, in severe cases, a life-threatening reaction called anaphylaxis.
• Food intolerance — usually a problem with digesting or processing a food, such as lactose intolerance. Symptoms are typically digestive — bloating, wind, cramps, loose stools — and come on more slowly. It is uncomfortable but not dangerous in the way a true allergy can be.

What a blood allergy test measures

A food allergy blood test measures IgE antibodies to specific foods. A raised IgE to a food you react to can support a diagnosis of allergy and help identify the culprit. This is genuinely useful for suspected true allergies, especially where symptoms are rapid or significant.

Where testing has real limits

Two important cautions are worth spelling out. First, a positive IgE result does not always mean a clinically important allergy — you can show antibodies to a food you eat without any trouble, so tests must be matched to your history. Second, many widely marketed "food intolerance" tests that measure IgG antibodies are not supported by good evidence. IgG often simply reflects foods you eat regularly, and using such results to cut out large food groups can lead to an unnecessarily restricted diet without helping your symptoms.

Focused panels when you already suspect the food

The 20-food panel above is the right choice when you cannot tell which food is responsible. If you already have a strong suspect, a smaller panel answers the question for less. The most common pattern — a child, or an adult since childhood, reacting to egg, milk or bread — has its own panel, and three other focused panels cover the non-food triggers that are often mistaken for a food reaction. Each tests four allergens plus Total IgE and costs £143:

For a single food that is not on any panel — a particular nut, fruit, fish or spice — type it into the search box on the booking page and build a custom allergy test from any of 185 individual allergens, from £99 for two. Remember these are IgE allergy tests: none of them, and no blood test, diagnoses an intolerance.

A sensible approach to food reactions

For suspected intolerances, a structured food and symptom diary — sometimes with a supervised elimination and reintroduction of specific foods — is often more revealing than any single blood test. Doing this with a dietitian helps avoid needlessly restrictive eating. For suspected allergy, targeted IgE testing guided by your symptoms is the more reliable route.

When to see a doctor

Seek prompt medical advice if you have had any sudden, severe reaction to food — swelling of the lips, tongue or throat, difficulty breathing, or faintness — as this may be a serious allergy needing urgent assessment and an emergency plan. You should also see a doctor if food-related symptoms come with red flags such as unexplained weight loss, blood in your stool, difficulty swallowing or persistent vomiting, which point away from simple intolerance and need proper evaluation.

Written by Dr Ibrar Ahmed — MBChB MRCP MRCGP PhD PG Dip (Cardiology)
Specialist interest: Cardiovascular Medicine · OneMedicine, CQC-registered clinic