Food intolerances constitute a large group of disorders characterized by the appearance of an unwanted reaction after the ingestion of a nutrient contained in a food.

Food intolerances have characteristics that clearly differentiate them from food allergies:

  • the body's reaction caused by food intolerances does NOT involve the body's defense system (immune system), unlike what happens in allergies
  • the manifestations of intolerances can occur hours, or even days, after the consumption of the responsible food, making it difficult to relate the observed effect to the ingested food. Allergic reactions to a food, on the other hand, appear immediately after eating or drinking it
  • the disorders caused by food intolerances are dose-dependent, this means that if a certain food is consumed in limited quantities, therefore below the maximum dose that the body is able to tolerate, it will not cause effects, while, in quantities above this dose, it will cause disturbances proportional to the quantity of food ingested. In allergies, however, the body's reaction never depends on the quantity of food consumed and even a very small dose determines the activation of the immune system, up to the potential anaphylactic shock
  • disorders resulting from food intolerance are less severe and appear graduallyon the other hand, those caused by food allergies are more severe and develop rapidly


Food intolerances manifest themselves with signs and disorders (symptoms) mainly affecting the gastrointestinal system. The most frequent include:

  • nausea
  • difficulty digesting (dyspepsia)
  • He retched
  • cramps
  • abdominal bloating
  • flatulence
  • diarrhea

However, it is not uncommon for ailments to appear in other areas of the body. For example, there may be marked redness on the skin (hives) that causes severe itching, or rapid and intense swelling of the mucous membranes (angioedema) or the appearance of scaly, itchy patches on the skin (eczema). In some cases, respiratory disorders such as asthma and rhinitis can occur; headache (headache) and dizziness are also frequently present in food intolerances, as well as drowsiness, chronic fatigue, anxiety and mild forms of depression.


Food intolerances can have various causes that allow them to be classified as follows:

  • enzyme intolerance, determined by the body's inability to digest certain nutrients due to the absence, decrease or reduced activity of the enzyme (molecule that facilitates and speeds up the chemical reactions of the body) responsible for their transformation (metabolization). This type of intolerance, generally caused by an enzyme defect already present at birth (congenital) leads to the development of disorders (symptoms) related to the transformation of nutrients such as carbohydrates or proteins. In some cases, the enzymatic alteration appears over time or develops following diseases. The most frequent enzyme intolerance is lactose intolerance, the sugar present in the milk of all mammals (cow, sheep, goat, donkey , in addition to breast milk). It develops as a result of the progressive loss of the enzyme called lactase, a protein localized on the intestinal mucosa, capable of dividing lactose into its two components: glucose and galactose. In the absence of the enzyme lactase, the body is unable to digest lactose which, consequently, arrives in the intestinal tract called colon in quantities exceeding the absorption capacity of the intestinal wall. The lactose that remains inside the intestine ferments, resulting in the production of gas and the appearance of bloating (meteorism) and diarrhea, disorders (symptoms) that distinguish the person with "intolerance to this specific sugar
  • drug intolerance, due to the presence of pharmacologically active components in the food eaten. The so-called are an example vasoactive amines (tyramine, histamine and caffeine) contained in fish, chocolate and fermented products, or substances added to foods (food additives) such as dyes, flavor enhancers, preservatives, natural and artificial flavors
  • food intolerance with indefinite cause, due to a response of the organism on a psychological and psychosomatic basis. Examples are the effects due to self-suggestion that occur when you eat a food or a substance towards which you feel aversion or repulsion (food adversion)
  • secondary food intolerance, i.e. resulting from diseases. It generally involves the gastrointestinal tract, as happens in people suffering from inflammatory bowel diseases (IBD), gastritis, gastroesophageal reflux, gallbladder stones


The method for ascertaining (diagnosing) a "food intolerance is mainly based on the account of the changes in the person's health over time; however, since some signs and disorders (symptoms) are similar to those of food allergies, it is essential to exclude, through the "execution of targeted tests, the possibility that the cause of the disturbances is an" allergy.

When food intolerance is suspected, it is advisable to consult your doctor, who will be able to indicate the specialists to contact.

In any case, all tests for food intolerances that do not have solid scientific validity should be avoided.

Tests without scientific validity include:

  • IGg4 dosage
  • cytotoxic test
  • Alcat test
  • electrical tests (vegan test, Voll electroacupuncture, bioscreening, biostrengt test, sarm test, moratest)
  • kinesiological test
  • dria test
  • hair analysis
  • iridology
  • bioresonance
  • pulse test
  • auricular heart reflex

Unfortunately, many people rely on unqualified personnel, starting diets that involve the elimination of foods (elimination diets) based on the results of these tests, thus encountering possible deficiencies of essential substances for the body.

To find out about "lactose intolerance, however, there is a scientifically validated test which is currently considered the reference test (gold standard) known as the breath test. The test allows to ascertain lactose intolerance through the presence of hydrogen (H2) in the air emitted from the mouth (exhaled). The execution is simple and involves the assumption of a predetermined dose of lactose followed by the analysis, after a certain period of time, of the exhaled air. The presence of the hydrogen peak in the exhaled air is an indication of the fermentation of the unabsorbed lactose by the intestinal bacterial flora, the so-called good bacteria normally present in the intestine.

More and more people claim they suffer from gluten intolerance, known as gluten sensitivity, a condition not to be confused with celiac disease. In fact, the term celiac disease refers to a real allergy to gluten that triggers a reaction of the body's defense system (immune system) against the intestine, resulting in damage to the intestinal mucosa.

In the "gluten intolerance, on the contrary, there is no involvement of the immune system; the person suffering from it presents disorders (symptoms) such as abdominal pain, fatigue, headache, irritable bowel but does not have anti-gluten antibodies or lesions of the intestinal mucosa.

To ascertain (diagnose) the gluten sensitivity there are no specific exams; it is based on the present disorders and their improvement after a deprivation diet, as well as on the lack of specific antibodies for celiac disease and on the absence of intestinal lesions on biopsy. The certainty of the presence of gluten intolerance, therefore, is based on mostly on the exclusion of other diseases.


The official treatment (therapy) of the various forms of food intolerance provides for the exclusion from the diet of the substances or foods involved. Nevertheless, many Italian nutrition companies agree that the treatment cannot, and should not, be based on the simple elimination of foods but that, thanks to the support of professionals, it is necessary to aim for their replacement in the daily diet.

It is believed, in fact, that the exclusion diet can not only have a significant negative impact on the quality of life, also from a social and psychological point of view, but can also determine a condition of nutritional risk due to the lack of nutrients that could involve. In the presence of a food intolerance, the advice of a qualified health professional is of fundamental importance to manage it correctly and effectively in the long term on all fronts: social, nutritional, psychological.


Intestinal health is closely associated with food tolerance and good digestion.The latest research shows that the intestinal microbiota, that is the set of bacteria that live in the intestine, plays a very important role in regulating tolerance, immunological and otherwise, towards the substances ingested. An alteration in the balance of the bacterial flora, known as dysbiosis, often linked to a bad diet, could be the cause of the "increased inflammation" of the intestinal mucosa and the reduced tolerance to the substances that pass through it. In daily life, following a balanced diet complete with all the micro and macronutrients, as indicated in the Mediterranean diet, promotes the growth and maintenance of the intestinal microbiota. In some cases, on the advice of your doctor, it may be useful to take probiotics through the diet (yogurt, kefir, miso, fermented cheeses), or supplements, to promote the development of a favorable environment for digestion by rebalancing the intestinal flora and contributing to the prevention of intolerances.


Gray J., Chan W. Food intolerance Types: food aversion in Encyclopedia of Food Sciences and Nutrition (Second Edition). Academic Press; 2003

International Society of DAO deficiency. Food histamine (English)

Conti L. Food intolerances and allergies. Giunti publisher: Florence, Milan; 2011

Ministry of Health. Food allergies: act of address

Position Statement on Allergies, food intolerances and nutritional therapy of obesity and metabolic diseases

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