In a recent review article published in the journal Current Allergy and Asthma Reports, researchers examined the increasing cases of allergic reactions to various legumes used in plant-based diets beyond the well-known allergens like peanuts and soybeans.

Their findings indicate that non-priority legumes such as peas, lentils, and lupines are becoming significant allergen sources, necessitating large-scale studies and improved diagnostic measures to better understand and manage these allergies.

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Increasing popularity of plant-based foods

Over the past decade, there has been a significant increase in the consumption of plant-based dietary products, especially legumes, driven by the growing popularity of vegan diets perceived as healthier and more eco-friendly.

Legumes are rich in proteins, essential nutrients, and minerals, and their fiber components can benefit gut health and energy production. Despite these benefits, the rise in plant-based diets has coincided with an increase in reported legume allergies, potentially triggered by factors like lifestyle changes and environmental influences.

While well-known allergens such as soybeans and peanuts are regulated and labeled, other legumes like beans, peas, lentils, chickpeas, and lupines are emerging as significant allergen sources.

Peanuts and soybeans: well-known allergens

Peanuts and soybeans are the most common legume allergens, especially in countries like Germany, Austria, and Switzerland, often causing severe allergic reactions, including anaphylaxis.

Peanut allergies can range from mild to life-threatening and are linked to specific proteins like oleosins, which help distinguish severe reactions. Interestingly, peanut-allergic individuals may also react to other legumes due to cross-reactivity.

Soybean allergies are less common but can be severe, particularly in adults. Specific proteins in soybeans, such as PR10 protein (Gly m 4), can trigger strong allergic responses and can even refold after heating, making them resistant to digestion.

This can cause issues for people with related pollen allergies, highlighting the need to accurately identify allergens to improve diagnostic and therapeutic approaches.

Legume allergy investigation. Identification of single allergens mainly occurs via protein extraction from whole extracts using sera from well-characterized allergic patients in order to show their IgE-binding capacity in vitro. In addition, the in silico approach can be used. After identification of allergens in a whole extract they are purified from the natural source or produced recombinantly. The purified or recombinant allergen can subsequently be applied in diagnostic tests such as the basophil activation test (BAT) and mast cell activation test (MAT).

Lesser-known legume allergens

In contrast with soybean and peanut allergies, beans, peas, lentils, chickpeas, and lupine are emerging allergens that can cause severe reactions.

Bean allergies, though rare, may occur due to cross-reactivity with other legumes, resulting in oral mucosa, respiratory tract, and occasional skin reactions. Reports include instances of mung beans causing oral allergy syndrome (OAS) and broad beans triggering reactions, particularly when fried.

Pea proteins, common in meat substitutes, have caused severe allergic reactions in children and adults despite some studies suggesting safety for lipid transfer protein (LTP) allergic patients.

Lentils have also induced severe allergic reactions with symptoms resulting from ingestion, inhalation, or skin contact. Examples include children and adults experiencing anaphylaxis, skin reactions, and food-dependent exercise-induced anaphylaxis (FDEIA) after consuming lentils. Cross-reactivity with peanuts and other legumes is common, and more specific diagnostic tests are needed to assess these risks.

Chickpea allergies are infrequent but severe, sometimes leading to anaphylaxis post-consumption and exercise. Reports from the past have documented cases of anaphylaxis following chickpea consumption and subsequent exercise. These cases highlight the potential allergenic risk of chickpeas, especially for those with other legume allergies.

Lupine, used widely as a wheat and dairy substitute, poses allergy risks, potentially due to cross-reactivity with peanuts. Lupine allergens are considered “hidden allergens,” and reactions can vary depending on the species and protein content. Despite its use in various foods, the prevalence of lupine allergy remains uncertain, emphasizing the need for better diagnostic tools.

Cowpea, pigeon peas, and fenugreek have fewer reported cases of allergies, but they do contain potential allergens. Cowpea allergens have shown cross-reactivity with other legumes. Pigeon pea’s allergenicity has not been extensively studied, but its increasing use in vegan diets warrants further investigation. Fenugreek has caused occupational asthma and anaphylaxis, often in those with peanut allergies. Cross-reactivity between fenugreek and other legumes has been documented, suggesting a need for caution.

Conclusions

Many diagnostic methods are used to investigate legume allergies, including skin prick tests (SPT), oral food challenges, and various in vitro tests like the basophil activation test (BAT) and specific immunoglobulin E (IgE) tests.

Despite increasing diagnostic accuracy, most studies use in vitro IgE-binding assays due to the low number of allergic individuals. The rise in legume allergy cases highlights the need for more studies on allergen stability and processing effects. Food processing can change protein structures and affect allergenicity, so understanding these changes is crucial for safer food production. More research is needed, especially with the growing trend of vegan food.

Non-priority legumes (lupines, chickpeas, lentils, beans) can cause anaphylaxis, especially in those allergic to peanuts and soybeans. Although many allergens are identified, they are not used in commercial diagnostic tests. As vegetarian and vegan diets rise, improved tests and understanding of cross-reactivities are crucial for accurate diagnosis and prevention.