Food allergy vs. intolerance: what is the difference?

• Dietitian Sharon Jaeger explains that a food allergy is an immune system response that can be serious, while an intolerance mainly causes digestive discomfort.

If you have the same reaction to a certain food every time you eat it, such as an upset stomach or diarrhoea, you may think you have a food allergy, but it is more likely that you have a food intolerance. The key is to understand the differences between a food intolerance and a food allergy, so that you are better prepared to manage the way certain foods affect your body. So what is the difference?

Registered dietitian Sharon Jaeger, RD, says that food intolerances cause unpleasant and frustrating symptoms such as gastrointestinal discomfort, while the symptoms of food allergies are likely to be more serious and sometimes even fatal.

Understanding the causes and the symptoms

“The symptoms of an allergy and an intolerance can look similar, but one clear difference is how they affect your body”, says Jaeger. “An allergy is an immune system response, while isolated digestive problems generally point to a food intolerance”.

Food allergies can develop in adults, so you may have spent your whole life enjoying prawns only to have a reaction one day that seems to come out of nowhere. After eating a food you are allergic to, symptoms usually appear quickly, within 30 minutes to two hours. “When you eat the offending food, an immediate immune response is triggered”, says Jaeger. “This kind of reaction can be fatal if it is not treated straight away with an injection of epinephrine or adrenaline”.

Food intolerance

A food intolerance occurs when the body cannot properly break down a certain food or ingredient. Lactose intolerance, for example, is the result of an enzyme deficiency that stops the body from properly breaking down lactose, a sugar found in milk.

“Its symptoms can be inconvenient and uncomfortable, but they are not life-threatening”, explains Jaeger.

When do food allergies develop?

Food allergies often become apparent in childhood, especially through foods such as milk, nuts, eggs and soya. Sometimes, however, these allergies can develop later in life, so this is not always a safe bet. (Research suggests that the early introduction of potentially allergenic foods may help prevent peanut allergies in high-risk babies. If you are concerned, talk to your allergist.)

Intolerances and sensitivities can also develop or get worse with age. Once again, lactose intolerance is a common example: “As you get older, your body may produce less of the enzyme that helps digest the lactose in dairy products”, explains Jaeger.

How to tell whether you have a food allergy or an intolerance

These are some of the ways in which food allergies, intolerances and sensitivities are diagnosed.

1. Allergy testing

Skin allergy tests can identify the body’s reaction to allergens. A blood test can identify raised levels of the allergy antibodies produced by the immune system.

But determining the cause of a food intolerance or sensitivity is not an exact science. Apart from the hydrogen breath test for diagnosing lactose intolerance, there are no proven skin or blood tests for these problems.

2. Keep a food diary

You can keep a food diary to record what you eat, when you have symptoms and what they are. If you notice that a food or ingredient consistently causes you discomfort, it is likely to be an intolerance.

3. Try an elimination diet

You can work with your healthcare provider to start an elimination diet to help identify the cause of your discomfort.

If you have symptoms when you eat a certain food, then have no symptoms when you do not eat it, and the symptoms then return when it is reintroduced, this is part of the process of identifying a food intolerance.

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