What are the key clinical features that differentiate food intolerance from food allergy in patients presenting with gastrointestinal symptoms?

Key clinical features differentiating food intolerance from food allergy in patients with gastrointestinal symptoms include the nature, timing, and systemic involvement of symptoms. Food allergy, particularly IgE-mediated, typically presents with rapid-onset symptoms following ingestion of the allergen, often within minutes to a few hours, and may involve multiple organ systems including skin (urticaria, angioedema), respiratory tract (wheezing, cough), and gastrointestinal tract (colicky abdominal pain, vomiting, diarrhoea) NICE CG116. Non-IgE-mediated food allergy tends to have delayed gastrointestinal symptoms such as vomiting, diarrhoea, blood or mucus in stools, faltering growth, and may be associated with atopic conditions like eczema NICE CG116. In contrast, food intolerance usually manifests as isolated gastrointestinal symptoms without systemic allergic features, often with a delayed onset and dose-dependent severity, and lacks immunological mechanisms NICE CG116. Unlike food allergy, food intolerance does not cause anaphylaxis or involve IgE antibodies and is less likely to be associated with atopic disease or multisystem involvement NICE CG116. Additionally, food allergy symptoms are often reproducible on repeated exposure to the allergen, whereas food intolerance symptoms may be more variable and related to the quantity of food ingested NICE CG116. From an immunological perspective, food intolerance involves non-immune mechanisms such as enzymatic deficiencies or direct irritant effects on the gut, whereas food allergy involves immunocyte and enterocyte interactions leading to immune activation Patrick & Gall 1988. Therefore, the presence of systemic allergic signs, rapid symptom onset, reproducibility, and association with atopy strongly suggest food allergy, while isolated, dose-dependent gastrointestinal symptoms without systemic involvement point towards food intolerance NICE CG116; Patrick & Gall 1988.