Which foods should you avoid if you have a soy allergy?

What is a soy allergy?

Soy is a member of the legume family, which also includes beans, peas, lentils, and peanuts.

Found in many foods, soy is a common cause of IgE-mediated food allergies in infants and young children.

Zoë Palmer-Wright, a food intolerance expert says, "A soy allergy occurs when the body's immune system mistakes the harmless proteins found in soy for invaders and reacts by creating antibodies against them," says Palmer-Wright.

"As part of its over-reactive defence response, the body also releases lots of histamines to protect itself against the 'invader'. This histamine release causes the symptoms of coughing, wheezing, itching, and hives."

If you suspect you have a soy allergy, you should have this confirmed by taking an allergy test as soon as possible.

How do you know if you have a soy allergy?

If you have the following symptoms after eating soy or soy products, it could be a sign of an allergy:

• Skin redness.

• Itching.

• Rashes/hives.

• Coughing.

• Wheezing.

• Sneezing.

• Shortness of breath.

• Tingling in the mouth.

• Swelling in lips, tongue, or throat.

• Nausea.

• Dizziness.

• Stomach pains.

• Diarrhoea.

Soy allergy symptoms typically last for about 48 hours after consuming soy. In more serious cases, it can take a few days for symptoms to ease.

If an extreme reaction is not treated quickly, it could be fatal. This is caused if a reaction results in anaphylaxis, a systemic allergic response that essentially sends the body into shock.

Can you test for soy allergy at home?

Deaths from serious allergic reactions (anaphylaxis) due to food have declined over the past 20 years in the UK¹. However, the fact remains that some soy allergies can be life-threatening.

As you cannot predict how serious your allergy may be, you should not attempt to test at home. Instead you should speak to a medical professional who will be able to arrange the appropriate testing. There are various methods that can be used, including:

Allergy skin-prick testing

In allergy skin-prick testing, a very small amount of soy is introduced to the skin, typically on the arm, through a gentle pinprick. If the skin becomes itchy, red, or starts to swell, a soy allergy might be present.

Allergen-specific IgE blood tests

In allergen-specific IgE blood tests, a small amount of your blood is drawn and tested for antibodies you may have produced in response to exposure to soy.

"It's important that you do get tested to determine whether you have a true soy allergy or a sensitivity intolerance to soy. If a soy allergy is ruled out with testing by a medical professional, you may have a soy sensitivity instead," Palmer-Wright says.

IgG blood tests

These blood tests can be performed to check for soy sensitivity with an at-home testing kit.

A blood test will measure the number of specific antibodies in your bloodstream, known as immunoglobulin G (IgG) antibodies, which can assess your immune system's intolerance or sensitivity response to soy.

There is no evidence currently to support these blood tests as IgG circulates in healthy individuals who do not display symptoms of food allergies or sensitivities. These can often cause harm by people mistakenly eliminating key foods and nutrients from their diets. If there are any thoughts of an allergy, seek out medical advice first.

What foods should someone with a soy allergy avoid?

It can be difficult to decipher what foods are safe for people with soy allergy, particularly if you have a child who is allergic. According to food industry estimates, soy is found in an estimated 60% of processed foods². "With a soy allergy, your body can react to even a minuscule amount of soy, and because of this, you need to be careful to avoid all soy to prevent allergic reactions," says Palmer-Wright.

She explains that soy protein is found in soybeans (edamame), as well as many traditional Asian foods, such as:

• Tofu.

• Tempeh.

• Natto.

• Miso.

As well as soy, tamari, and shoyu sauces.

Soy can also be found in many meat substitutes such as vegetarian burgers, vegetarian sausages, and other food made from TVP (textured vegetable protein).

Ingredients in the following food items should be reviewed as well:

• Yoghurt.

• Cheese.

• Ice cream.

• Flour.

"Soy is a common ingredient in some infant formulas, protein powders, and snack bars. Because it is such a common ingredient in processed foods, you'll need to read all food labels to check for soy," says Palmer-Wright.

Additionally, steer clear of products containing HSP (hydrolysed soy protein). You might find this in:

• Sweets.

• Cereals.

• Sauces.

• Salad dressings.

• Soups.

You must also be mindful when eating out in restaurants, making sure to check the details of what you're ordering and asking waiting staff about ingredients. The same goes when a friend or family member is cooking for you.

How is a soy allergy reaction treated?

Palmer-Wright explains that the only way to prevent a reaction to soy is by avoiding soy completely. But, this might be difficult and it might seem that soy is everywhere.

She says your doctor may suggest you carry antihistamines or if required, an injectable adrenaline (epinephrine) with you at all times, in case of a flare-up.

In rare cases, anaphylactic shock can occur, meaning your blood pressure drops suddenly, your airwaves narrow, and your pulse weakens. Symptoms of anaphylaxis specifically include:

• Swelling of the mouth, tongue, and throat.

• Difficulty breathing.

• Wheezing.

• Coughing.

Acute anaphylaxis can be fatal in just 15 minutes, so immediate medical intervention is required, and you should call 999 (if in the UK) for an ambulance.

"Auto-injectable adrenaline (epinephrine) can be used for treating allergic reactions causing anaphylaxis. It is a life-saving medication when someone is experiencing a severe allergic reaction."

However, even if you have used injectable adrenaline, if you or another person are showing signs of anaphylaxis, you must call the emergency services right away.

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Can you develop a soy allergy later in life?

Palmer-Wright explains that, in most cases, soy allergies develop and are diagnosed in early childhood.

Many children outgrow their allergy by the age of three, but the majority of children will outgrow it by 10 years of age. However, some people do remain allergic to soy for the rest of their lives.

In some cases, soy allergies can develop later in life. This can come as a surprise, with people starting to experience reactions to foods they've previously eaten without any issues. Some adults will develop an allergy to some foods in the legume family, but not others.

Further reading

1. Food anaphylaxis in the UK - analysis of national data.

2. Allergy UK soy factsheet.