D2.05 - A Retrospective Study Characterising the Types of Presentation of Soy Allergy in Adults

Soy, a member of the legume family, is classified as a major food allergen. As an inexpensive and nutritious protein source, it is widely used in various forms, such as whole beans, flour, milk, sauces, and processed into texturizers, emulsifiers, and protein fillers, making it challenging to avoid. Its prevalence as a compound ingredient in processed foods further complicates identification. Soy allergy can present in various form and severity. Currently, there is limited evidence on how patient history and investigation results correlate with clinical severity in the adult population. This retrospective study aims to characterise and understand the distribution of various presentations of soy allergy in adults.

A retrospective study was conducted looking at all patients referred to the Royal Brompton Hospital allergy service from 2021 – 2023 with investigations into soy allergy. 187 patient records were reviewed, of which 40 (21%) had a diagnosis of soy allergy. Patients that were deemed non-allergic or had an unclear diagnosis or had missing records were excluded from the study. 

Majority of patients (31/40, 77.5%) with reactions to soy were diagnosed with pollen food syndrome. This is in keeping with soy milk being the most common form of soy that patients reacted to. Five patients (12.5%) had legume allergy, one patient (2.5%) had a primary soy allergy and three patients (7.5%) were allergic to fermented soy only. Nine patients had severe reactions requiring adrenaline, seven of which had a diagnosis of pollen food syndrome. The remaining two patients had anaphylaxis to fermented soy, both to tempeh. Patients allergic to fermented soy were confirmed with food challenges, two of which reacted to tempeh and one reacted to soy sauce. All three patients with an allergy to fermented soy had a negative specific IgE to soy bean, Gly m 4, Gly m 5 and Gly m 6. The patient with a primary allergy to soy had positive specific IgE to Gly m 6 and soy bean. Blood results for those with legume allergies were variable. No correlation was found between the prevalence of soy allergy with peanut allergy or cow’s milk allergy.

This study offers insight into the types of soy allergies observed in adults. As a common ingredient in many foods, understanding the patterns of soy allergy presentation is essential not only for accurate diagnosis but also for guiding risk management.