Soy is one of the most common food allergens in the United States, and soy allergy affects about 0.4% of children. Soy is not as common an allergen for adults. About half of children will outgrow their soy allergies by the age of 7.
Soy Allergy Symptoms
Soy allergies may have symptoms that range from itching of the mouth to difficulty breathing. Symptoms of soy allergy usually appear within a few minutes to two hours of eating soy ingredients. They may include:
- Skin rashes, such as eczema, or hives
- Swollen, red, watery eyes (allergic conjunctivitis)
- Gastrointestinal symptoms, such as abdominal pain, nausea, diarrhea, and/or vomiting
- Difficulty breathing, wheezing, or coughing
- Swelling of lips, tongue, or face (angioedema)
- Shock (anaphylaxis)
Some people with peanut allergies may have cross-reactions with soy protein. People with soy allergies may cross-react with peanuts or other legumes, such as beans or peas. However, most people with soy allergy can safely tolerate other legumes. You should not avoid foods because of fear of cross-reaction, because avoiding foods may lead to developing new sensitivities.
Some people with birch pollen allergies who have oral allergy syndrome may have oral itching or swelling of the mouth, tongue, or throat after eating soy.
Infants and Soy Allergies
Soy is one of the most common allergens for infants who have not yet begun eating solid foods, because they may be fed soy-based infant formula. It is rare for babies to have a traditional Ig-E mediated food allergy to soy, but some babies may develop a Milk-Soy Protein Intolerance or Food Protein Induced Enterocolitis Syndrome (FPIES).
Infants will usually develop these sensitivities within a few months of birth, and most will outgrow them by the age of two. The most common symptom is blood-streaked stool. Some babies will experience vomiting, distended bellies, or lack of weight gain. Very rarely, babies with FPIES may experience shock.
Soy Allergies and Labeling Laws
Soy is one of the most common food allergens in the United States and is covered under FALCPA. This law requires that the presence of soy be listed in plain English as "soy," "soya" or "soybean" on labels, either in bold print in the list of ingredients or following the ingredient list after the word "Contains."
However, FALCPA contains an exception for refined soybean oil and soy lecithin –- both are pervasive ingredients in most processed foods, and are not required to be disclosed in a “contains” statement. While most people with soy allergies can tolerate the small amount of soy protein that remains in refined soybean oil and soy lecithin, both of these ingredients may cause allergic reactions in highly sensitized people.
Eating Out with Soy Allergies
Eating out is very challenging with a soy allergy. Most restaurants cook in soybean oil, since it is the cheapest vegetable oil. Soy is a pervasive ingredient in processed foods.
Your best bet for eating out with a soy allergy is to choose a cuisine that does not traditionally use soy, and to talk with the chef before you go to the restaurant. Because of the FALCPA exception for soybean oil and soy lecithin, foods listed as “soy-free” on chain restaurant web sites may contain these ingredients.
You may be more likely to find a small, locally-owned restaurant where you can establish a relationship with the chef and have your food specially prepared than to find a chain restaurant with food that is completely free of soy.
Eating Vegetarian with a Soy Allergy
Eating a vegetarian diet with a soy allergy is an extra challenge. Most vegetarian convenience foods contain soy, although many newer vegetarian cookbooks avoid relying on soy as a protein source. Whole grains, legumes, and dairy products can help you to have a balanced diet and meet your protein needs.
Living with Soy Allergies
You will need to carry an emergency first aid kit with you, including contact information, antihistamines, and an epinephrine auto-injector if prescribed by your doctor.
Kattan JD, et al. Milk and soy allergy. Pediatr Clin North Am. 2011 Apr;58(2):407-26, x.
NIAID-Sponsored Expert Panel. Guidelines for the Diagnosis and Management of Food Allergy in the United States: Report of the NIAID-Sponsored Expert Panel. The Journal of Allergy and Clinical Immunology. Volume 126, Issue 6, Supplement, Pages S1-S58, December 2010
Wood, R.A., et al. The Natural History of Soy Allergy. J Allergy Clin Immunol. 2010 Mar;125(3):683-6.