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Soy Allergy

A food allergy is a hypersensitivity reaction that involves the immune system (see “What is an allergy?”). Although up to 20-30% of people believe they have a food allergy, studies show that between 2% and 5% of people suffer from a definite food allergy (see “Food allergy”).

  • Soy is a protein-rich plant source derived from soybeans
  • Soybeans are a member of the bean (legume) family. The majority of people who are allergic to soy do tolerate other legumes, however, a small number may react to other legumes such as beans and peanuts

How common is soya allergy?

  • Immediate allergies to soy are generally uncommon, but more common in children than adults
  • Soy allergy can however develop at any time, even in those who previously tolerated soy
  • Soya allergy can co-exist with cow’s milk protein allergy, more commonly in the delayed type allergies, in which soya and cow’s milk allergy can co-exist in about half of patients (see “Delayed food allergy”)
  • It is much less common for people with immediate type cow’s milk allergy to also have an allergy to soy (about 10%)
  • The most common type of soy allergy is “immediate” type (IgE-mediated) food allergy
  • This type of reaction typically occurs within minutes but may present up to 2 hours after eating the food
  • Most allergic reactions to soy are mild, causing hives (urticaria), swelling or vomiting. Occasionally reactions are severe causing breathing difficulties or circulation issues.
  • Some reactions to soy are a “delayed type allergy” which typically occurs several hours or even days after eating the soy. This usually manifests as skin rashes (usually eczema) or gut symptoms
How is soy allergy diagnosed?
  • The first step is for the doctor to hear all the details about what was eaten and exactly what reactions occurred. This will help indicate whether the reaction was an allergy or not and if it was an allergy, what kind of reaction it was and whether it was mild or severe
  • For immediate reactions, a blood test and/or skin prick tests can be done to show the presence of the IgE antibodies. If these tests are negative an immediate type of allergy is almost always ruled out. A “positive” result supports but does not prove an immediate type of food allergy unless the values are very high
  • Skin prick tests are done by placing a few drops of soy (fresh soya milk or specially manufactured soya extract) on the skin and making a prick through the droplet
  • In cases which are uncertain, the allergist may recommend a supervised food challenge to test for soy allergy. This entails giving initially tiny, then increasing amounts of soya to the person in a controlled setting (see oral food challenge tests)
  • Delayed reactions are more difficult to diagnose as there are no laboratory tests to aid diagnosis. If a delayed reaction is suspected, then your allergy doctor will advise an elimination diet and then reintroduction of soy-containing foods. This is best done by a trained allergy specialist (see delayed food allergy)
Treatment of soy allergy
  • If you allergic to soy, you must avoid eating soya milk, soya yoghurt and all soy containing products
  • Soy protein is present in a large amount of everyday foods and is often a “hidden” allergen in particular foodstuffs. With the food labelling laws in South Africa, products containing soy should be clearly indicated. Parents need to read all labels and exclude the names provided in the list below
  • Avoiding foods is difficult! A dietician experienced in managing food allergy will provide advice, recipes and education on how to achieve a nutritious and complete diet
What to look for on labels that may indicate soy is present
  • Bean curd
  • Carob
  • Emulsifier
  • Lecithin
  • Miso
  • Monosodium glutamate (MSG)
  • Protein extender
  • Soya, soybean, soyabeans
  • Soy protein, soy isolate, soy concentrate
  • Soy flour, soy fibre, soy albumin, soy oil
  • Soy milk
  • Soy nuts, soy sprouts
  • Soy sauce, shoyu sauce
  • Stabiliser
  • Starch
  • Tofu
  • Textured vegetable protein (TVP)
  • Thickener
  • Vegetable gum
  • Vegetable broth
  • Vegetable starch
Emergency treatment
  • Soya may be difficult to avoid completely and accidental reactions do occur
  • Caregivers in schools, family members and friends should know about the allergy and what to do in an emergency. A detailed “action plan” should be provided in case of reactions. This should clearly describe the difference between mild and severe reactions as well as what to do if different types of reactions occur. The action plan should be highly visible at home and in the school/work environment
  • The patient should have access to their emergency treatment at all times. For milder reactions an anti-histamine may be enough. For severe reactions, injectable adrenaline will be needed
  • The allergy doctor should decide on whether a person with allergy is at risk to have a severe reaction. People with previous severe reactions or at risk of severe reactions should carry injectable adrenaline with them at all time, preferably in the form of an auto-injector
  • People who have been prescribed an autoinjector must be trained when and how to use it and carry it with him/her at all times
  • Soy allergic individuals should wear a Medic alert or similar bracelet, especially if they have a severe allergy or also have asthma
Will the soy allergy be outgrown?
  • Soy allergy may be outgrown
  • Children with soy allergy should see their allergy doctor regularly to check their growth and nutrition and to make sure they are managing to avoid the food and are able to treat any accidents correctly
  • The allergy doctor will monitor the allergy yearly either by skin prick or blood test. If those tests indicate that the allergy may have been outgrown then you (or your child) may be brought into the hospital or clinic as a day case for a soy challenge
  • A soy challenge is a supervised procedure in which increasing doses of soy protein are fed to the patient under close observation to check for reactions. Such a soy challenge is used to decide if tolerance has developed and if the person is no longer allergic to soy (see oral food challenges)
Download our “Soy allergy” leaflet for free