Common meat-free proteins might trigger soybean, peanut allergies in some people

Many people who want to cut back on meat are turning to legumes, which are high in protein, vitamins, and fiber. Allergies to legumes, such as soy and peanuts, are common and fatal. Are meat-free proteins made of legumes dangerous to patients who are allergic to specific legumes, even if the legumes are different? Dr. Mark Smits and his colleagues at Utrecht University Medical Center set out to investigate.

“Both protein consumption and the world’s population are increasing which leads to an urgent demand for sustainable protein sources,” said Dr. Thuy-My Le, senior author of the study published in Frontiers in Allergy. “An increase in the consumption of legumes may increase the number of allergies to these foods. Furthermore, these new legumes may elicit allergic complaints in already legume-allergic patients. Therefore, we investigated how often sensitization and allergy to different legumes occur in these patients.”

Any other name for an allergy, Food allergies occur when the immune system misidentifies food proteins as a threat and produces Immunoglobulin E (IgE) antibodies. Individuals who have been sensitised to food may develop allergy symptoms if exposed to it again. Patients who are allergic to one food may also be allergic to another: this is known as co-allergy. Co-allergies are often accompanied by co-sensitization, which occurs when patients produce IgE antibodies against multiple foods. Cross-reactivity, in which IgE antibodies bind to proteins from different foods because their structures are similar, may cause co-sensitization.

Co-sensitization can lead to a diagnosed co-allergy, but it does not always: it is possible to be co-sensitized to a food and not have a reaction when eating it. So, do patients who are allergic to specific legumes react to other legumes?

Smits and colleagues recruited legume-allergic patients from the University Medical Center Utrecht’s Allergology Clinic and divided them into six groups based on allergies: peanuts, soybeans, green peas, lupines, lentils, and beans. Allergies were validated in all patients through an oral food challenge or a positive IgE test combined with a history of reactions. IgE antibodies against the other legumes were tested in each group separately.

“We showed that a large number of patients produced antibodies against more than one legume,” said Dr. Kitty Verhoeckx, second author of the study. “However, clinical data showed that only a small part of these patients had actual symptoms.”

Co-sensitization is common among legumes, but not always co-allergy.
Co-sensitization to additional legumes was observed in all six patient groups, with nearly a quarter of patients sensitised to all legumes. Almost all of the patients in the bean allergy group developed sensitivities to other legumes. Patients who were allergic to green peas, lupines, or lentils were more likely to be sensitised to other legumes, whereas patients who had peanut or soybean allergies were not.

The researchers also investigated which of these patients had documented co-allergies to various legumes. Only a small number of patients had clinical symptoms as a result of the high co-sensitization rate. Co-allergies to green peas, lupine, lentil, and bean were uncommon in peanut and soybean-allergic patients, but patients who were allergic to this second group of legumes were more likely to be allergic to peanuts or soybeans.

Patients who were allergic to peanuts were frequently also allergic to soybeans, and vice versa. Peanut sensitization was linked to clinically significant co-allergy in almost all other legume groups. However, the researchers cautioned that the study should be expanded to a larger group and co-allergies confirmed with oral food challenges before determining how clinically relevant this co-sensitization is in practise.

“Legumes are an attractive sustainable protein source, but allergic reactions in the already legume-allergic population cannot be excluded as antibodies in the blood of legume-allergic patients frequently react to different legumes,” said Le.

“However, this reaction does not always lead to a clinically relevant food allergy. Introduction of novel foods into the market should be accompanied by an appropriate assessment of the risk of developing (new) food allergies.”

Is there a risk from meat-free proteins derived from legumes, even if the legumes are different? Dr. Mark Smits and his colleagues at Utrecht University Medical Center set out to investigate.