Food intolerance: symptoms, causes and GP guidance

Food intolerance describes difficulty digesting certain foods, leading to gut or systemic symptoms. It is common and often confused with food allergy, but the two are very different.

This page explains what food intolerance is, how it differs from allergy, which foods are commonly involved, how GPs assess symptoms, and when testing or referral is appropriate.

These articles are intended as educational sources, not diagnostic nor taking place of a proper medical assessment. If you need help, please book an appointment with one of our GP’s.

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What is food intolerance?

Food intolerance occurs when the body has difficulty processing certain foods or food components. Unlike food allergy, it does not involve the immune system and does not cause anaphylaxis.

Symptoms are usually delayed and dose-dependent, meaning they may worsen with larger amounts of the trigger food.

Seek urgent medical advice if you have:

Rapid onset swelling, wheeze or breathing difficulty after eating
Collapse or severe dizziness after food exposure
Persistent vomiting or inability to keep fluids down
Unintentional weight loss or ongoing blood in stools

Common symptoms of food intolerance

Symptoms vary between individuals and may include:

Bloating or abdominal discomfort
Excess wind
Diarrhoea or loose stools
Nausea
Abdominal cramping
Fatigue or headaches in some people

Symptoms often develop hours after eating rather than immediately.

Food intolerance vs food allergy

It is important to distinguish between the two.

Food intolerance

Digestive difficulty
Symptoms are uncomfortable but not life-threatening
Delayed onset is common
Amount eaten matters

Food allergy

Immune-mediated reaction
Symptoms occur rapidly
Can cause swelling, breathing difficulty or collapse
Requires urgent medical assessment

Suspected food allergy should always be assessed urgently.

Common food intolerances

Lactose intolerance

Caused by reduced lactase enzyme activity.

Bloating, diarrhoea and wind after dairy
Symptoms improve with reduced lactose intake

FODMAP intolerance

Certain carbohydrates are poorly absorbed and fermented in the gut.

Common in people with IBS
Symptoms include bloating and altered bowel habit

Non-coeliac gluten sensitivity

Some people report symptoms related to gluten without coeliac disease.

Diagnosis requires exclusion of coeliac disease first
Symptoms overlap with IBS

Food additives and natural chemicals

Some people react to:

Caffeine
Alcohol
Artificial sweeteners
Histamine-rich foods

Reactions are variable and individual.

How GPs assess suspected food intolerance

Assessment usually focuses on:

Symptom pattern and timing
Relationship to specific foods
Bowel habit and weight changes
Red flag symptoms
Family history of coeliac or bowel disease

Diagnosis is usually clinical rather than test-based.

Food intolerance testing: what is and is not helpful

Tests that may be useful

Coeliac disease blood tests, if gluten is still in the diet
Lactose breath testing in selected cases

Tests that are not recommended on current evidence

IgG food sensitivity tests
Hair testing
Unvalidated “food panels”

These tests are not diagnostic and often lead to unnecessary long-term dietary restriction.

“Should I do a food sensitivity test?”

Patient: I’ve seen IgG food sensitivity tests and hair tests online. Should I do one to find my trigger foods?

GP: It’s a common question. The issue is that these tests are not reliable for diagnosing food intolerance. IgG often shows exposure to foods you eat, not a harmful reaction, and hair testing is not considered a validated medical test for intolerance.

Patient: So what should I do instead?

GP: A safer approach is to start with medical checks where appropriate, such as coeliac testing if you are still eating gluten, then use a structured food and symptom diary. If needed, we can guide a time-limited elimination and reintroduction plan, ideally with dietitian input, so you avoid unnecessary long-term restriction.