Food Intolerance
Symptoms, Causes & Treatment
Food intolerance is extremely common, affecting up to 20% of the population. It causes digestive symptoms that can significantly impact daily life and nutrition. Accurate identification of the trigger is essential before unnecessary dietary restriction is implemented.
What is Food Intolerance?
Food intolerance describes non-immune reactions to specific food components that cause digestive symptoms. The most common types include lactose intolerance, FODMAP intolerance, non-coeliac gluten sensitivity, and histamine intolerance. Food intolerance is distinct from food allergy (an IgE-mediated immune reaction) and coeliac disease (an autoimmune condition). Accurate diagnosis guides targeted dietary management without unnecessary restriction.
Symptoms of Food Intolerance
Food intolerance causes delayed digestive symptoms, typically occurring within hours of eating trigger foods. Symptoms differ from the immediate immune reactions seen in food allergy.
Bloating and digestive discomfort after eating specific foods · Diarrhoea, nausea, or abdominal pain after ingestion · Flatulence and belching · Symptoms develop within hours of eating · No anaphylaxis or immediate immune reaction
Anaphylaxis after food ingestion (hives, throat swelling, breathing difficulty) — call 999 · Severe allergic reaction requiring epinephrine · Symptoms of coeliac disease crisis with severe malabsorption
Sudden throat swelling, hives, difficulty breathing, or collapse after eating — this is anaphylaxis. Call 999 immediately. Use EpiPen if available. This is a food allergy emergency, not food intolerance.
What Causes Food Intolerance?
Food intolerance arises from impaired digestion or absorption of specific dietary components. It is distinct from food allergy and requires different investigation and management.
Lactose intolerance results from deficiency of lactase enzyme, causing undigested lactose to be fermented by colonic bacteria, producing gas, bloating, and diarrhoea. Prevalence varies by ethnicity (up to 90% in East Asian adults).
Non-coeliac gluten sensitivity (NCGS) causes GI and extra-intestinal symptoms after gluten ingestion, without the autoimmune or villous atrophy seen in coeliac disease. Coeliac disease must be excluded before NCGS is diagnosed.
Coeliac disease is an autoimmune condition triggered by gluten, causing villous atrophy in the small intestine. It affects 1 in 100 people. Diagnosis requires anti-TTG IgA antibodies and duodenal biopsy on a gluten-containing diet.
Fructose malabsorption causes bloating, cramping, and diarrhoea when fructose exceeds absorption capacity. Common triggers include apples, pears, honey, and high-fructose corn syrup. A low-fructose or low-FODMAP diet resolves symptoms.
Histamine intolerance results from reduced capacity to metabolise dietary histamine (from wine, aged cheese, processed meat, fermented foods). Symptoms include headache, flushing, GI disturbance, and urticaria.
True food allergy (IgE-mediated) is distinct from food intolerance. It causes immediate allergic reactions including urticaria, angioedema, and anaphylaxis. The most common allergens are peanuts, tree nuts, milk, eggs, wheat, soya, fish, and shellfish.
Key Risk Factors
Diagnosing Food Intolerance
Food and symptom diary, hydrogen breath testing, coeliac antibodies, and supervised elimination diets are the validated diagnostic approaches.
Treatment for Food Intolerance
Treatment is dietary modification guided by accurate diagnosis. Lactase supplements, gluten-free diet, low-FODMAP diet, and allergen avoidance are the main approaches.
Supportive Measures
Keep a food and symptom diary for 2–4 weeks. Identify and eliminate trigger foods systematically with dietitian support. Use lactase supplements for dairy. Read food labels carefully. Avoid self-diagnosing food intolerance without professional guidance.
Long-Term Food Intolerance Management
Coeliac disease requires lifelong gluten-free diet with annual review. FODMAP intolerance is managed through structured dietitian-guided elimination and reintroduction. Lactose intolerance is managed through lactase supplements and dietary modification. Food allergies require ongoing allergen avoidance and emergency management plans.
When to Seek Help
Sudden throat swelling, difficulty breathing, severe urticaria, or collapse after eating — this is anaphylaxis. Call 999 immediately. Use adrenaline auto-injector (EpiPen) if available.
See a GP if digestive symptoms are significantly impacting quality of life, if you suspect coeliac disease, or if you have had any allergic reaction to food. Hydrogen breath testing and coeliac antibodies can be arranged by a GP.
Managing Food Intolerance Safely
Accurate diagnosis of food intolerance prevents unnecessary dietary restriction while identifying genuine triggers.
Keep a food and symptom diary for 2–4 weeks before any dietary change. Record what you eat, how much, and when symptoms occur. This guides accurate dietary assessment and prevents unnecessary restriction.
If you suspect lactose intolerance, try lactase enzyme supplements before dairy meals or switch to lactose-free alternatives. Many people with lactose intolerance can tolerate small amounts of dairy, particularly hard cheeses and yoghurt.
If coeliac disease is suspected, see your GP for blood tests (anti-TTG IgA) before starting a gluten-free diet. Once on a gluten-free diet, tests become negative and diagnosis cannot be confirmed without a formal gluten challenge.
Work with a FODMAP-trained dietitian rather than self-managing a low-FODMAP diet. Unsupervised FODMAP restriction causes nutritional deficiencies and unnecessarily restricts foods that were well-tolerated.
If you have a confirmed food allergy, carry an adrenaline auto-injector (EpiPen) at all times, wear a medical alert bracelet, and have a written allergy action plan. Inform restaurants and food handlers of your allergy.
Attend annual review if diagnosed with coeliac disease. Monitoring includes anti-TTG antibodies, bone density scan, and nutritional blood tests (ferritin, B12, folate, vitamin D) to detect complications of malabsorption.
Getting Treatment for Food Intolerance
A GP can arrange hydrogen breath testing, coeliac blood tests, and dietitian referral for low-FODMAP assessment. Food allergy requires specialist allergy clinic referral. An online consultation is a convenient first step for suspected food intolerance.
Expert clinical advice, when you need it.
Food Intolerance — Frequently Asked Questions
Food intolerance involves a delayed, non-immune reaction to specific foods, causing digestive symptoms hours after eating. Food allergy is an immediate immune (IgE-mediated) reaction causing urticaria, swelling, and potentially anaphylaxis within minutes. Food allergy requires an EpiPen; food intolerance is managed by dietary modification.
Lactose intolerance is caused by deficiency of the lactase enzyme, which normally digests lactose (milk sugar) in the small intestine. Undigested lactose passes into the colon where bacteria ferment it, producing gas, bloating, and diarrhoea. A hydrogen breath test or 4-week lactose elimination trial confirms the diagnosis.
Coeliac disease must be excluded before starting a gluten-free diet, because antibody tests become negative on a gluten-free diet and diagnosis cannot then be confirmed without a formal challenge. Blood tests (anti-TTG IgA) should be done while eating a normal gluten-containing diet.
Coeliac disease is an autoimmune condition causing villous atrophy when gluten is ingested. Non-coeliac gluten sensitivity (NCGS) causes similar symptoms but without the autoimmune damage or villous atrophy seen in coeliac disease. Coeliac disease must be excluded by blood tests and biopsy before NCGS is diagnosed.
FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols) are short-chain carbohydrates that are poorly absorbed in the small intestine. Fermentation by colonic bacteria causes gas, bloating, cramping, and altered bowel habit. Common high-FODMAP foods include onions, garlic, apples, beans, wheat, and lactose-containing dairy.
Testing for food intolerance through blood (IgG antibody tests) sold online or in health food shops is not evidence-based and is not recommended by NHS or allergy specialists. Positive results from IgG tests simply reflect food exposure, not intolerance. The only validated approaches are elimination diets, supervised by a dietitian, combined with careful symptom tracking.
People with confirmed food allergy should avoid all forms of the allergen, carry an adrenaline auto-injector (EpiPen) at all times, wear a medical alert bracelet, inform all restaurants and food handlers of their allergy, and have a written allergy action plan. Allergen immunotherapy may be an option for some allergies.
A GP can arrange a hydrogen breath test for lactose intolerance, blood tests and biopsy for coeliac disease, and refer to a specialist dietitian for low-FODMAP assessment. Food allergy requires referral to a specialist allergy clinic. An online GP consultation is an effective first step for suspected food intolerance.