What is food intol­er­ance?


You eat something – and your body rebels. The reason could be a food intolerance or even an allergy. But what exactly is the difference? We discuss the potential indications and symptoms and when a test is advisable.

What is food intolerance?

Food intolerances are non-allergic reactions of the body’s digestive system to food. While lactose intolerance is the most common, fructose (fructose intolerance), gluten (coeliac disease) and histamine can also trigger an intolerance.

Causes of food intolerance 

Intolerances can be genetically inherited, or triggered by other illnesses or psycho­somatic causes. In the case of lactose intolerance, scientists know that a certain genetic predisposition (e.g. Asian ancestry) is responsible for the decreased activity of the lactase enzyme over the course of a person's life and the subsequent onset of an intolerance.

Food intolerance: common symptoms

  • severe bloating
  • flatulence
  • stomach cramps
  • stomach ache
  • diarrhoea
  • constipation
  • fatigue

Symptoms worsened by: stress and an unhealthy lifestyle

There are multiple symptoms of a food intolerance. Depending on the intolerance, the symptoms usually appear between 1 and 4 hours after eating, sometimes even later, when carbohydrates (types of sugar) are fermented in the large intestine. Stress and an unhealthy lifestyle can worsen the symptoms, but aren't the cause.

Intolerance or allergy: the difference

With an intolerance, the body is unable to digest a certain substance and usually rebels with pain in the gastrointestinal area. The extent of an intolerance varies from person to person. For example: some people with a lactose intolerance can still tolerate a whole glass of milk while others will react to much smaller amounts. Unlike with an allergy, however, the immune system is not involved.

While 2 to 8% of people suffer from a food allergy, up to 20% suffer from a food intolerance.

Food allergy: hypersensitive reaction of the immune system

With a food allergy, the immune system reacts to harmless proteins in food. Adults are most commonly allergic to hazelnuts, walnuts, celery, apple and kiwi fruit. Allergies likely to cause the most severe reactions are those caused by peanuts, seafood or sesame. Children typically react to cow’s milk, eggs, wheat, peanuts and nuts or fish. Since spice mixtures also contain minute amounts of allergenic substances, check them well before using.

Common symptoms

  • itching in the mouth
  • reddened skin
  • swelling in the face
  • shortness of breath
  • in the worst case, an anaphylactic shock occurs, which can be life-threatening

Avoid triggers if you have an allergy: allergy sufferers must avoid the trigger foods at all costs.

Ways of testing an allergy or intolerance?

A food allergy is diagnosed by self-observation and skin and blood tests. A food intolerance is much more difficult to diagnose because it can’t be detected with an allergy test. The test for a food intolerance is therefore relatively pragmatic: a diet based on omission. For example: the person affected abstains from fructose for two to four weeks. If the condition doesn’t change, it’s probably not due to this food. However, if the condition disappears, this points to an intolerance.

Dietary change for fructose intolerance

Abstinence: 2-4 weeks

Up to 5g fructose per day Approx. 1 apple / pepper

Test phase: 4 weeks

In what quantity are individual foods tolerated?

Dietary change: long term

After the dietary change, the symptoms should disappear.

Help if you're affected

The aha! Swiss Allergy Centre works on behalf of the almost three million people in Switzerland who suffer from an allergy or intolerance. The aha! infoline provides free personal advice from Monday to Friday (8.30 am to 12.00 noon).

When to see a doctor

It’s advisable to see a doctor if symptoms persist for several weeks, occur several days a week or affect your quality of life. You should definitely see a doctor if your body weight drops or – to avoid malnutrition – if the symptoms are so bad that you can only eat very little at all.

The basic rule is: people who react to food should clarify exactly which ingredients they are sensitive to and adjust their diet accordingly. The best person to help with this is a trained nutritionist.

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