Soya allergy: The causes, symptoms and how to treat it

What is soya?

Soya beans are a member of the legume family along with peanuts, peas and lentils.

Foods made from soya beans, such as tofu, tempeh and soya milk, are often favoured in vegan or vegetarian diets as a protein-rich substitute for animal products.

If you generally avoid soya-based foods, you are still likely to be consuming soya in your diet from the 60% of manufactured foods that contain it in the form of soya sauce, soya flour, soya oil, or soya lecithin¹.

In an allergic reaction to soya, the body mistakenly identifies the ingested or inhaled soya protein as a foreign invader. This leads to activation of the immune system, resulting in inflammation.

Soya allergies can be regulated by an antibody called immunoglobulin E (IgE). This is known as an ‘IgE-mediated allergy’ and leads to a potentially serious reaction within minutes.

A non-IgE-mediated reaction is less likely to be severe, does not involve IgE and generally takes longer to present; usually within 48 hours of soya exposure.

It is estimated that 0.3% of the European population are allergic to soya². It is therefore a much rarer condition than cow’s milk allergy, which affects 6% of Europeans³.

What are the main symptoms of a soya allergy?

Symptoms of a soya allergy can range from mild to severe and can involve different areas of the body following exposure.

Mild reactions can present as irritation, tingling and swelling in the lining of the mouth and throat.

The rest of the digestive system can also be affected with abdominal pain, sickness and diarrhoea.

Skin irritation, including itchiness, redness and hives or airway obstruction, can also occur.

In severe cases, an allergic reaction to soya can lead to a serious condition called anaphylaxis, resulting in difficulty breathing and a drop in blood pressure that can be fatal.

What are the causes of a soya allergy?

Allergies are a result of a fault in the body’s immune system.

Oral allergy syndrome (also known as pollen-food syndrome) is the most common form of soya allergy. In this condition, soya protein causes a reaction in those with a pre-existing allergy to birch, hazel or alder pollen.

This is because the protein in soya has a similar structure to proteins in pollen, which means it can also bind to the cells that trigger an immune system reaction.

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What foods can soya be hidden in?

Soya is a popular product and is widely used in a range of common foods. This makes it difficult for consumers to avoid completely, even if they are not vegetarian or vegan.

Aside from the whole forms of soya such as edamame, soya milk, tofu and tempeh, soya can be used as a texturiser (texturised vegetable protein), emulsifier (soya lecithin), or protein filler in a range of products including crisps, soups, ready meals, sauces and desserts¹.

Soya flour is also a common ingredient in many processed foods, breads and cakes.

In the UK, soya is classed as one of the 14 major food allergens. Legislation therefore requires its presence to be clearly stated on product packaging.

Even with a diagnosis of soya allergy, you may not need to cut out all forms of soya from your diet.

Products such as soy sauce or soya lecithin have much of the soya protein removed.

Refined soya oil is considered safe for those with a soya allergy, however cold-pressed soya oil should be avoided as the soya proteins are not completely removed during processing⁴.

What’s the difference between a soya allergy and soya intolerance?

Soya intolerance may lead to reactions that are similar to soya allergy, but the mechanisms behind them are very different.

A soya intolerance does not involve the immune system, and it therefore cannot be detected or tested for via a blood test.

Intolerances are more common and predominantly impact the digestive tract, although other areas of the body can also be affected.

Intolerances can be due to a variety of causes, including difficulty in digesting and absorbing a food or an underlying presence of irritable bowel syndrome (IBS).

How can you treat a soya allergy?

If you suspect you may have an allergy to soya, the most important thing to do first is speak to your GP or family doctor.

An IgE-mediated soya allergy can be tested for with a simple skin-prick test along with a chat with an allergy specialist clinician.

If a soya allergy diagnosis is confirmed, you will be advised to remove soya products from your diet.

Your diagnosis will determine how strict you need to be with cutting out soya.

If your tests are negative but you still suspect that soya is causing you problems, you may wish to work with a dietitian to investigate further.

What are the benefits of soya?

Although soya has been portrayed as a controversial product, research is showing that it is not only safe for humans to consume, but actually beneficial.

Soya contains an abundance of plant protein, required for growth, development and recovery from injury or stress.

Soya is low in saturated fat and high in micronutrients and isoflavones that are found to reduce menopausal symptoms and provide protection against heart disease and some types of cancer.

For someone with a soya allergy, what are the alternatives that provide the same benefits?

If you are avoiding soya in your diet, don’t worry, the benefits found in soya can be gained from other whole plant foods!

• Eating alternative legumes, such as lentils, black beans, peanuts and peas, will provide protein, fibre and micronutrients such as iron.
• Soy milk can be replaced with other plant milks high in protein such as pea milk. Choose plant milks fortified with calcium and vitamin D for extra bone-health benefits.
• Including nutritious dark leafy greens in your diet will provide a source of calcium and iron. Low-oxalate greens, such as kale and spring greens, will provide the most absorbable form of calcium.
• Raw and unsalted almonds, cashews, and pumpkin seeds are fantastic sources of protein and micronutrients. Walnuts, chia seeds, flaxseeds and hemp seeds contain good levels of omega 3 fatty acids.
• Base your meals on healthy wholegrains such as wholewheat pasta, brown rice, buckwheat or quinoa. Wholegrains are surprisingly high in protein and will provide a good amount of fibre and micronutrients to boot.
• Nutritional yeast (known as ‘nooch’) can be a ‘cheesy’ addition to the diet without needing soya-based vegan cheeses. Make it up into a cheese sauce using ingredients such as cashews, white beans, lemon juice, garlic and salt. Nutritional yeast provides protein and zinc and some are fortified with vegan B12.
• Check labels on ready-made foods carefully. Cooking from scratch with whole plant foods is a great way to eat when avoiding soya, as you won’t have labels with long lists of ingredients to check.

This information does not replace individualised medical advice. If you have any concerns, it is always best to consult your doctor or dietitian for personalised advice.

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References

1. https://www.allergyuk.org/information-and-advice/conditions-and-symptoms/36-types-of-food-allergy#download_access
2. https://www.ecarf.org/en/information-portal/allergies-overview/soya-allergy/
3. https://pubmed.ncbi.nlm.nih.gov/24816523/
4. https://www.food.gov.uk/sites/default/files/media/document/food-allergen-labelling-technical-guidance.pdf