Soy belongs to family of pulses, making its seed the edible part of the plant. Its seed is rich with proteins, carrying high biological values so it also carries nutrient values as well. There is about 35% of pure protein in dry soy seed. Allergenic properties of soy proteins have been documented in the 1980s, when it was widely spread in Asia and USA, and today it’s basically all over the world especially in vegetarian cuisine.
Allergy towards soy is caused by those same proteins found in the seed, especially from the so called “stashed” proteins. These can be found in huge amounts in seed and serve as the building material for the new plant. At least two stashed proteins have been identified as allergenic – vicilyn and legumyn. These proteins are extremely resistant towards heat and are usually left intact after thermal processing of soy. Soy products are widely used in the food industry, especially for adding texture and emulsifying of products. It is also a main ingredient of many refined oils but in this case there aren’t many allergenic proteins in there.
Soy can cause all kinds of allergy symptoms ranging from itchiness, swelling of the oral cavity and throat, gastrointestinal reactions, respiratory problems, skin reactions as well as fatal reactions like anaphylactic shock, loss of breath, and drop of blood pressure and so on. By breathing the soy powder in you can induce respiratory problems like asthma. Patients who develop symptoms of allergy after inhalation might tolerate soy in some other form. Soy dust has been the cause of epidemic of asthma between 1981 and 1987 in Spain after it was loaded off in Barcelona ports.
Characteristics of the Allergy
Up until today, the frequency of soy allergy hasn’t been researched. It was described mainly as an allergy affecting small children with eczema, which stop experiencing symptoms after 1 or 2 years of avoiding soy in their diet. About 1-4% of children with eczema react to soy rich foods. Allergic reactions on soy products are less common with adults.
Since soy seeds originate from pulses, there was a serious concern about other pulses like peanuts having equal allergic properties. This concern was based on assumption that similar proteins in related ingredients cause a similar reaction, which is known as cross reaction. Reserve proteins in peanuts or peas are very similar to those found in soy. Most individuals who are allergic to soy are tolerant to peanuts, except patients who are suffering from allergies to pollen. But this doesn’t mean that there are no patients who are showing cross reactions with allergies on multiple pulses.
Diagnosis is usually done by a clear and concise overview of the history of the disease so that there is a close correlation established between allergic reaction and soy. Since soy is commonly one of those invisible parts of processed foods, this is not always simple. With a simple skin test diagnosis can easily be established.