Allergies can cause significant upset in the stomach and intestines. This reaction occurs because the immune system mistakenly identifies a harmless food protein as a threat, triggering a defensive response within the gastrointestinal (GI) tract. The body’s reaction involves releasing chemicals that cause inflammation and physical symptoms like cramping, vomiting, and diarrhea. Understanding this mechanism helps distinguish between a true immune reaction and other forms of food sensitivity.
True Allergy Versus Food Intolerance
Distinguishing a true food allergy from a food intolerance is important because the underlying biological mechanisms are different. A true food allergy involves the immune system, whereas a food intolerance primarily involves the digestive system. Intolerance results from an inability to properly digest a food component, often due to a lack of necessary enzymes (e.g., lactase deficiency in lactose intolerance).
Allergies are classified into Immunoglobulin E (IgE)-mediated and non-IgE-mediated reactions. IgE-mediated allergies are rapid-onset reactions where symptoms appear within minutes to an hour of eating, often involving the skin, respiratory system, and GI tract. These reactions occur when IgE antibodies trigger chemical release, carrying the risk of a severe systemic reaction.
Non-IgE-mediated allergies involve other parts of the immune system, characterized by a delayed onset of symptoms (hours or even days after consuming the trigger food). These reactions are confined to the gastrointestinal tract and do not cause the immediate anaphylactic shock seen in IgE reactions. Intolerances are generally dose-dependent, meaning small amounts of the food can often be consumed without issue, and they do not involve an immune response.
How Immune Responses Affect the Digestive Tract
The symptoms of an allergic reaction in the gut are caused by immune cells located in the lining of the digestive tract. When a person with an IgE-mediated allergy consumes a trigger food, the allergen binds to IgE antibodies attached to mast cells and basophils in the gut wall. This binding causes degranulation, where these cells release inflammatory chemical mediators into the surrounding tissue.
Histamine is a chemical released, acting on the gut in several ways. It increases the permeability of small blood vessels, leading to localized swelling and fluid leakage into the tissue and gut lumen. Histamine also stimulates the smooth muscle lining the intestines, causing forceful contraction, which results in abdominal cramping, pain, and accelerated transit leading to diarrhea.
Other mediators, such as leukotrienes, are released and contribute to inflammation and increased mucus production in the intestinal lining. This combination of muscle spasms, fluid shifts, and inflammation causes the gastrointestinal distress associated with a true food allergy. Irritation can lead to vomiting as the body attempts to expel the threat.
Specific Digestive Disorders Caused by Allergies
Several medical conditions are recognized as allergic disorders primarily affecting the digestive system. Eosinophilic Esophagitis (EoE) is characterized by a buildup of eosinophils (a specific type of white blood cell) in the lining of the esophagus. This accumulation causes chronic inflammation, which can lead to scarring and narrowing of the swallowing tube.
EoE symptoms include difficulty swallowing (dysphagia), chest pain that mimics heartburn, and food frequently getting stuck in the esophagus. This disorder is a non-IgE or mixed-type allergic condition, often triggered by common foods like milk, wheat, or soy. Food Protein-Induced Enterocolitis Syndrome (FPIES) is a severe non-IgE reaction that typically affects infants and young children.
FPIES is defined by repetitive vomiting and diarrhea that starts approximately two to four hours after ingesting the trigger food, often leading to severe dehydration. Because of its delayed onset and GI symptoms, FPIES is frequently misdiagnosed as food poisoning or a viral stomach infection. Eosinophilic Gastroenteritis (EGE) is a related disorder where eosinophils infiltrate the stomach or small intestine, causing abdominal pain, nausea, and vomiting.
Diagnosis and Management Strategies
Diagnosis of an allergic cause for digestive upset begins with a detailed patient history and symptom tracking, often involving a food diary to correlate foods with the onset of symptoms. For immediate, IgE-mediated reactions, skin prick tests or blood tests measuring food-specific IgE antibodies help identify the allergen. A positive test result must be interpreted alongside the patient’s actual symptoms to confirm a diagnosis.
Diagnosing non-IgE conditions like EoE or FPIES is more involved because standard IgE tests are not useful. EoE requires an endoscopy with a biopsy to assess the esophageal lining and count eosinophils. The definitive diagnostic tool for non-IgE reactions remains the medically supervised oral food challenge, where the suspected food is consumed in a clinical setting to monitor for a reaction.
Management of a confirmed food allergy centers on strict avoidance of the identified trigger food. Individuals with IgE-mediated allergies may be prescribed an epinephrine auto-injector for emergency treatment of a systemic reaction. For chronic conditions like EoE, treatment includes specialized elimination diets or medications to reduce eosinophilic inflammation in the GI tract. Consulting with specialists like allergists and gastroenterologists is important for establishing an accurate diagnosis and a comprehensive management plan.