Are Food Allergy And Food Intolerance The Same?

From gluten to dairy to salicylates, reactions to foods are on the rise. In fact, up to 38% of people believe they react negatively to certain foods [1].

When you experience symptoms, it’s easy to presume the worst and think that you have an allergy. However, most food reactions are actually down to a sensitivity or an intolerance.

While they can feel similar, food allergy, food sensitivity and food intolerance all involve different cellular mechanisms. Crucially, this means they have different degrees of severity.

Let’s take a look at all three.

What is a food allergy?

A true food allergy is an inappropriate reaction by the body’s immune system to the ingestion of food [2]. In other words, you eat something your body doesn’t like—and it quickly tells you it’s not happy.

It’s believed that between 2% and 8% of the UK population suffers from food allergies. According to the National Institute of Allergy and Infectious Disease, common food allergens include:

  • Dairy
  • Eggs
  • Peanuts
  • Wheat
  • Soy
  • Fish
  • Shellfish
  • Tree nuts: walnuts, cashews and almonds

The first time a person eats a food that their body perceives as harmful, the immune system fires up and creates a special protective protein. This protein is known as immunoglobulin E, or IgE, and it’s tailor made to fight against a specific food.

If a person eats that food again, the IgE proteins are ready and raring to go. Hoards of IgE proteins attach to other cells in your body, commanding them to release a chemical called histamine to combat the invader. It’s the histamine that causes the typical symptoms of an allergic reaction.

What are the symptoms of a food allergy?

The severity of symptoms differs between individuals. Common signs of an allergic reaction include:

  • Rash, hives or itchy skin
  • Nausea
  • Stomach pain
  • Diarrhoea
  • Chest pain
  • Shortness of breath
  • Swelling of the airways

In extreme cases, a food allergy can cause anaphylaxis. This can lead to a loss of consciousness, and even death.

What is a food sensitivity?

A food sensitivity also involves the immune system, but the reaction is generally less severe in the short-term. Rather than IgE, the body produces a different protein known as IgG.

Unlike its fast-acting cousin IgE, IgG can take a while to take effect. This means that a person could eat a food to which they’re sensitive but not experience any symptoms until a few days later.

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What are the symptoms of a food sensitivity?

IgG is found all around the body, so symptoms of food sensitivity can appear anywhere [3]. Some signs include:

  • Fatigue
  • Fever
  • Bloating
  • Nausea
  • Itchy skin
  • Joint pain
  • Brain fog

Food sensitivities are more likely to be dose-dependent. This means that if a person eats more of a food to which they’re sensitive, their symptoms will feel worse.

The good news is that, while true food allergies are for life, a food sensitivity can disappear in time. This usually requires temporary avoidance of the food in question and a focus on improving gut health.


Food allergy vs food intolerance infographic

What is a food intolerance?

Unlike food allergies and food sensitivities, food intolerances don’t directly involve the immune system. Instead, different components of the digestive system react to foods or parts of foods.

Sometimes, this can be due to the lack of a certain enzyme. People who are lactose-intolerant, for example, don’t have enough of the enzyme lactase to be able to break down the sugar in milk [4].

Other common food intolerances include:

  • Sulfites (including those found in wine and dried fruit)
  • MSG
  • Artificial colours
  • Caffeine
  • Natural sugars (collectively known as FODMAPs)

Some of these intolerances cause an increase in the production of certain inflammatory messengers in the body, while others can stimulate the immune system indirectly. It’s also believed that our gut microbiome plays a role in the development of intolerances [5].

What are the symptoms of food intolerance?

Food intolerance symptoms are more likely to appear in the digestive system. Some signs include:

  • Gas and bloating
  • Constipation
  • Diarrhoea
  • Cramping
  • Nausea

How to diagnose a food allergy or intolerance

As you can see, there are some shared symptoms of food allergies, food sensitivities and food intolerances. So how can you know which type of reaction you have?

People with a severe food allergy tend to know about it. However, there are also ways you can test for reactions:

Food allergy: this can be diagnosed by the skin-prick test. A less common approach is an elimination diet with a double-blind food challenge—but this must be supervised, as it carries a risk if the person has a severe allergy. To be blunt: there’s no point in working out you’re allergic to tree nuts if the investigation ends up killing you.

Food sensitivity: it’s possible to carry out a food sensitivity test. While this isn’t diagnostic, it can provide useful insight into which foods may be problematic. It also gives clues about a person’s gut health.

Food intolerances: the best approach is to carry out an elimination diet. This involves a person eating exclusively non-reactive foods for three to four weeks, then introducing potentially problematic foods back into the diet one at a time. If reactions occur, it’s possible to pinpoint which food is the culprit.

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What to do if you have a food allergy or intolerance

If you believe you’ve experienced an allergic reaction to food, you should arrange an appointment with your GP. They will be able to arrange a test to confirm whether it’s a true allergy or not.

If you suspect you have a food sensitivity or food intolerance, you have a couple of options. You can undertake an elimination diet and then test foods by reintroducing them. This can be confirmative if you think you already know what’s causing problems—and illuminating if you have no idea. For extra guidance on conducting an elimination diet, you may wish to speak to a Functional Medicine Practitioner or Registered Nutritional Therapist.

Another option is to undertake a Food IgG Finger Prick Test. This looks at your blood chemistry to see which IgG proteins are in your blood, thus giving you some insight into how your body is reacting. This sort of test should always be analysed in conjunction with other signs and symptoms.

Remember, a critical part of tolerating our food is our gut health. If you’re sensitive or intolerant to lots of foods, it may be an indication that your gut needs some attention.





Fiona Lawson BA (Hons) DipCNM mBANT is a Registered Nutritional Therapist and health writer. She is a member of the Complementary and Natural Healthcare Council (CNHC) and the Institute for Functional Medicine (IFM). As Content Director of Healthpath, Fiona is on a mission to help people take charge of their own health. Read more about Fiona on her practitioner page.

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