A true, IgE-mediated allergy to Brussels sprouts is possible, though it is quite rare. When people experience discomfort after consuming this food, the reaction is far more often a food intolerance rather than a genuine immune system response.
Differentiating Allergy from Intolerance
The most frequent adverse reactions to Brussels sprouts are caused by digestive mechanisms, classifying them as an intolerance, not an allergy. An intolerance is a non-immune reaction, typically limited to the digestive system, involving difficulty breaking down certain food components. Symptoms are generally unpleasant but not life-threatening.
The primary culprits behind a Brussels sprouts intolerance are complex carbohydrates and sulfur compounds. Brussels sprouts contain raffinose, a trisaccharide that the human small intestine cannot break down because it lacks the necessary enzyme, alpha-galactosidase.
Undigested raffinose travels to the large intestine, where gut bacteria ferment it, producing gases like hydrogen, carbon dioxide, and methane. This fermentation results in common symptoms like flatulence, bloating, abdominal cramping, and sometimes diarrhea. Additionally, the vegetable contains sulfur compounds, which gut bacteria convert into substances that give the resulting gas its characteristic odor. These digestive issues are dose-dependent, meaning a larger serving is more likely to cause discomfort.
True Allergic Reactions and Triggers
A true Brussels sprouts allergy involves the immune system, specifically the production of immunoglobulin E (IgE) antibodies in response to a protein in the vegetable. The immune system mistakenly identifies this protein as a threat, triggering the release of inflammatory chemicals like histamine. This reaction can affect multiple systems and is potentially severe.
While a specific allergen has not been fully characterized, it is presumed to be a protein, possibly a Lipid Transfer Protein (LTP), based on findings in related vegetables. Symptoms of this rare IgE-mediated allergy can include the rapid onset of hives or a rash, facial or throat swelling, and Oral Allergy Syndrome (OAS), which causes itching or tingling in the mouth.
More severe reactions can involve respiratory distress, such as wheezing or difficulty breathing, or a drop in blood pressure. The most serious outcome is anaphylaxis, a systemic, potentially life-threatening reaction that requires immediate medical attention. Due to the shared family lineage of the Brassicaceae family, an individual allergic to Brussels sprouts may also experience cross-reactivity with other cruciferous vegetables like cabbage, broccoli, or kale.
Diagnosis and Management
If a true allergy to Brussels sprouts is suspected, consultation with an allergist is the next step for accurate diagnosis. The process begins with a thorough review of the patient’s medical history, focusing on the timing and nature of symptoms after ingestion, followed by specific testing to confirm IgE sensitization.
The allergist may perform a skin prick test, which involves placing a small amount of Brussels sprout extract on the skin and monitoring for a localized reaction. Alternatively, a blood test can measure the level of IgE antibodies specific to Brussels sprouts. These tests do not confirm a clinical allergy alone, but they indicate sensitization, which must be correlated with the patient’s symptoms.
Management of a confirmed Brussels sprouts allergy requires strict avoidance of the vegetable and any food containing its components. Given the potential for cross-reactivity, the allergist may recommend avoiding other Brassicaceae family members. For individuals diagnosed with a severe allergy, carrying an epinephrine auto-injector is standard practice to treat accidental exposure and prevent anaphylaxis.