Food intolerance: what is it and how does it affect our health?

What is food intolerance? 

Food intolerance is one of the two types of negative reactions of our body to food, one of its components or to food additives. Food intolerance, also known as pseudo-allergy, has a pharmacological, toxic or metabolic origin. It is an adverse, non-immunological reaction to the consumption of certain foods.

Food allergy, on the other hand, involves an immunological mechanism, i.e. a set of acute or chronic digestive and extra-digestive clinical manifestations, linked to an immune response against food allergens. This activation leads to the formation of IgE (immunoglobulin type E) antibodies, which in turn allows the release of other substances, such as histamine, responsible for the main allergic symptoms, which occur suddenly and may become severe.

These two forms of reactions are often confused. Food intolerance involves irritation, most often in the intestine and the colon. It may be caused by a specific enzyme or substance missing in the digestive system, which prevents or limits the proper digestion or absorbtion. Food intolerance requires a certain amount of food to cause discomfort.

What are the common symptoms of food intolerance? 

Symptoms associated with food intolerance can vary depending on the foods consumed and on individual sensitivity.

These symptoms, which can be painful and uncomfortable, can include:

• Nausea, vomiting,
  
• Abdominal pain,
  
• Diarrhoea,
  
• Bloating,
  
• Heartburn,
  
• Headaches,
  
• Cold sweats,
  
• Skin reactions (redness, pimples),
  
• Muscle and/or joint pain,
  
• Significant fatigue,
  
• Sleep disorders,
  
• Irritability, nervousness.
  

Some symptoms are more serious and can lead to anaemia. Food intolerances can also contribute to metabolic problems or systemic inflammatory and autoimmune diseases.

What causes food intolerance? 

Food intolerances can be caused by different substances. Lactose and gluten are the best known ones. However, there are also factors that contribute to food intolerance, such as the consumption of alcohol, ultra-processed foods, stress and certain medications.

Gluten intolerance 

Gluten is a protein found in the germ and in the husk of certain cereals (wheat, spelt, small spelt, kamut, rye, oats). In people who are intolerant to gluten, it induces a reaction in the body that causes inflammation and destruction of the intestinal mucosa.

Gluten intolerance can lead to coeliac disease, a chronic intestinal immune disorder. A reliable diagnosis of this disease requires a fibroscopy.

Lactose intolerance

Lactose is a sugar contained in milk, among other things. Lactase is an enzyme whose purpose is to digest lactose. In the absence of lactase, lactose is fermented by bacteria and transformed into gas, leading to lactose intolerance. A respiratory test can be carried out to determine the quantity of hydrogen exhaled, which is high in the case of lactose intolerance. It must be distinguished from allergy to cow's milk protein.

Fructose intolerance

Fructose is a natural sugar found in most fruits and vegetables and in honey. People with fructose intolerance suffer from a disorder of fructose metabolism. It is no longer absorbed and is broken down by the bacteria in the intestinal flora into gas and fatty acids.

Other intolerances 

Other intolerances may be due to the presence of tyramine (some cheeses, chocolate, herring), histamines (fermented foods and beverages, smoked foods, canned fish, avocados, figs, grapes, etc.), glutamate, sulphites (wines, dried fruits) and other food additives in the food we consume.

How can food intolerance be diagnosed? What is the treatment? 

If food intolerance is suspected, it is best to see a doctor. You will be asked to describe precisely all the symptoms experienced, the foods you suspect are responsible for these symptoms, and your family medical history.

The doctor will then be able to prescribe additional tests, which will enable him or her to eliminate the possibility of a food allergy. These examinations include skin and blood tests. If your symptoms are caused by food intolerance and not a food allergy, the results of these tests will be negative as it does not involve a direct immune response.

The doctor may also refer you to a gastroenterologist as part of the coordinated care pathway.

Diagnosis of food intolerance can be tricky and time-consuming, as repeated consumption of the suspected food over a certain period of time must be associated with the onset of symptoms. The doctor may advise the complete elimination of the food that causes the symptoms from your diet, and then its gradual reintroduction.

The treatment of food intolerances generally consists of prescribing a specific diet, with the elimination of the food in question. For example, lactose-free milk, gluten-free foods, or a FODMAP diet. If poorly tolerated food is eliminated from your diet, the symptoms disappear within hours or days. Seeing a nutrition specialist (registered dietician or nutritionist) may be helpful in maintaining a balanced diet.

What health conditions can be caused by food intolerance? 

The most common conditions that may be caused by food intoleraces include:

• Celiac disease,
  
• Gastric ulcer,
  
• Irritable bowel syndrome.
  

These intolerances could also favour other pathologies such as

• Migraine,
  
• ENT disorders (sinusitis, ear infections, Meniere's disease, etc.),
  
• Allergic asthma,
  
• Skin conditions (acne, psoriasis, eczema).
  

There is no way to prevent a food intolerance.


Food intolerances can have more or less serious consequences on our health. In everyday life, it is essential to check the complete list of ingredients of a product you buy, in order to avoid developing the symptoms of any known allergy or intolerance. The ingredient can sometimes be found under different names, so it is essential to be extremely vigilant, especially in the case of severe allergic reactions.