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Tuesday, August 12, 2025

Food intolerance


Definition

Food intolerance is a non-immunological, adverse reaction to certain foods or food components, leading to difficulty digesting or processing them. Unlike food allergy, it does not involve the immune system producing IgE antibodies, and it is generally not life-threatening. Symptoms are often delayed, dose-dependent, and related to the amount of food ingested.

Pathophysiology

Food intolerance occurs when the body has difficulty processing or metabolising a certain food component, often due to:

  • Enzyme deficiencies (e.g., lactase deficiency causing lactose intolerance)

  • Chemical sensitivities (e.g., reactions to histamine, caffeine, or sulfites)

  • Pharmacological reactions (e.g., vasoactive amines in certain foods)

  • Additive or preservative sensitivity (e.g., tartrazine, monosodium glutamate)
    Unlike allergies, these reactions do not trigger mast cell activation through IgE and typically cause gastrointestinal or systemic discomfort rather than acute anaphylaxis.

Common Types of Food Intolerance

  1. Lactose intolerance

    • Cause: lactase enzyme deficiency

    • Foods: milk, cheese, cream, yogurt

    • Mechanism: undigested lactose ferments in the colon, producing gas and osmotic diarrhoea

  2. Fructose intolerance

    • Cause: fructose malabsorption or hereditary fructose intolerance (enzyme deficiency in aldolase B)

    • Foods: fruit, honey, high-fructose corn syrup

    • Mechanism: poor absorption leads to fermentation and osmotic effects in the gut

  3. Gluten intolerance (non-coeliac)

    • Cause: non-allergic, non-autoimmune sensitivity to gluten proteins in wheat, barley, rye

    • Distinct from coeliac disease (autoimmune) and wheat allergy (IgE-mediated)

  4. Histamine intolerance

    • Cause: deficiency or reduced activity of diamine oxidase (DAO) enzyme

    • Foods: aged cheese, wine, cured meats, fermented products

    • Mechanism: excess histamine leads to flushing, headaches, hives, gastrointestinal upset

  5. Food additive intolerance

    • Examples: sulfites (wine, dried fruits), monosodium glutamate (processed foods), artificial colours like tartrazine

    • Mechanism: pharmacological effects or enzyme inhibition

Risk Factors

  • Genetic predisposition (enzyme deficiencies often inherited)

  • Gastrointestinal conditions (e.g., irritable bowel syndrome, small intestinal bacterial overgrowth)

  • Age-related enzyme decline (e.g., lactase levels drop after weaning)

  • High intake of processed or preserved foods

Clinical Presentation

Symptoms usually occur within a few hours but may be delayed up to 48 hours, depending on the type and quantity of food consumed. Common symptoms include:

  • Gastrointestinal: bloating, abdominal pain, diarrhoea, constipation, excessive gas, nausea

  • Dermatological: flushing, rashes, urticaria (non-allergic)

  • Neurological: headaches, migraines, fatigue

  • Respiratory: nasal congestion (rare, non-allergic mechanism)

Symptoms are dose-dependent and may be cumulative (build up after repeated exposure).

Diagnosis

Diagnosis is clinical and often involves exclusion of other conditions:

  • Detailed dietary and symptom history

  • Food and symptom diary to identify patterns

  • Elimination diet: removal of suspected foods for 2–6 weeks followed by reintroduction to confirm intolerance

  • Hydrogen breath tests for lactose or fructose malabsorption

  • Blood or genetic tests for hereditary conditions (e.g., hereditary fructose intolerance, coeliac disease exclusion)

There is no specific IgE or skin-prick test for food intolerance, as these test immune-mediated reactions.

Management

1. Dietary Modification

  • Identify and avoid trigger foods using elimination and reintroduction process

  • Lactose intolerance: lactose-free dairy or lactase enzyme supplements

  • Fructose intolerance: low-fructose diet, avoid high-fructose corn syrup and certain fruits

  • Histamine intolerance: avoid histamine-rich foods and alcohol, possibly DAO enzyme supplements

  • Sulfite sensitivity: avoid sulfite-containing foods and drinks

2. Enzyme Supplementation

  • Lactase: lactase tablets or drops taken with dairy to aid digestion

  • DAO supplements: taken before histamine-containing meals (effectiveness varies)

3. Symptom Management

  • Antispasmodics (e.g., hyoscine butylbromide 10–20 mg orally up to three times daily) for cramping

  • Probiotics to support gut microbiota balance in some cases

  • Adequate hydration, especially in diarrhoea

4. Nutritional Support

  • Ensure adequate nutrient intake despite restrictions (e.g., calcium supplementation if avoiding dairy)

  • Dietitian involvement for balanced meal planning

Prognosis

  • Most food intolerances are chronic but manageable with dietary adjustments

  • Quality of life improves significantly once trigger foods are identified and avoided

  • Some intolerances (e.g., post-infective lactose intolerance) may resolve over time

Prevention

  • No definitive prevention for genetic enzyme deficiencies

  • Gradual introduction of potential trigger foods in children may help identify intolerance early

  • Safe food handling and minimal consumption of highly processed foods reduce chemical additive exposure





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