The prevalence of food allergy seems to be on the rise and more and more people are avoiding foods because of a perceived allergy. Any food protein, including soy, can cause allergic reactions in sensitive individuals. But even though soy protein is one of the eight foods responsible for approximately 90 percent of food-induced allergic reactions in the United States, soy allergies remain relatively rare. A nationally representative telephone survey found that only approximately 1 out of 2,500 adults reported having a doctor-diagnosed allergy to soy protein. Allergy to milk was 40 times more common than to soy. Children are more likely to be allergic to soy than adults, which is not surprising since food allergies are less common in adults than children. And by age 10, an estimated 70 percent of children will outgrow their soy allergies.
Reactions to soy allergy tend to also be much more mild than reactions to other allergens like peanuts. Few anaphylactic and fatal reactions to soy allergy have been reported throughout the world whereas peanut allergy causes acute reactions with respiratory problems, and skin- and gastrointestinal symptoms. It’s a puzzling difference since soybeans and peanuts are both legumes and are botanically closely related, sharing cross-reacting antigens.
Recently, Danish scientists set out to determine why peanut and soy allergies differ.
For their study, 10 young adults (5 women and 5 men) ingested 100 grams of soybeans, which provided about 40 grams of protein. Blood was drawn before the participants consumed the soybeans, and then one, three and 24 hours afterwards. Unexpectedly, using two different assays, scientists could detect protein in the blood of only one of the 10 participants and even in that one person, the level was extremely low. If protein does not enter the blood, it can’t cause an immune response. This finding suggests that during digestion, soy protein is completely converted into amino acids, the building blocks of protein. In contrast to soy, previous research has shown that peanut protein is readily detected in the blood after the ingestion of peanut protein. The authors of this study concluded that their findings may explain the apparently weak allergenicity of soy protein by comparison with peanut protein in allergic subjects.
Lund et al. Clinical and Translational Allergy 2013, 3:6 doi:10.1186/2045-7022-3-6