Food Allergies: Causes and Risk Factors

While many people experience adverse reactions to certain foods , true allergic diseases are less common than one might think. Despite this, the number of people suffering from food allergies is continuously increasing. An important problem, therefore, which currently affects about 2-7% of adults and 6-13% of children.
The incidence of food intolerances is much higher (that to lactose , for example, reaches values ​​of over 90% in some ethnic groups), but as we have repeated on several occasions, they should not be confused with allergies because they do not involve the immune system .


Causes and Risk Factors

What are the risk factors for food allergies?


L ‘ atopy , which is the genetic predisposition to develop allergic reactions to ingestion or inhalation of allergens, is more common in families with allergy sufferers. This does not mean that food allergies are handed down from generation to generation according to Mendel’s laws , but that, statistical data in hand , children of allergic parents are more likely to develop them. It has been calculated that the risk of atopy for a child with both allergic parents fluctuates between 47 and 100%, against 13% of children with no family history.
However, this inheritance has some peculiar characteristics:

  • the symptoms can change considerably from parents to children, both in terms of severity and localization of the symptoms (for example, the parent, when he suffers an allergic reaction, may complain of respiratory problems, while the child may suffer from skin rashes );
  • the allergy can develop towards completely different antigens. The parent, for example, may be allergic to drugs, while the child may become sensitized to pollen or food .

Antigen exposure

Whenever the body comes into contact with an antigen, i.e. with a protein that is not its own, it produces antibodies against it. Theoretically, therefore, our body should react and develop antibodies against all food proteins , as food represents our most intimate contact with the external environment. Fortunately, this happens with pathogens but not with food, because the immune system recognizes food proteins as foreign but harmless substances, thanks to a mechanism, called tolerance, which involves the intestinal mucosa.and the lymphoid tissue associated with it (defined GALT, acronym for Gut Associated Lymphoid Tissue, which translated into Italian means, in fact, Lymphoid Tissue Associated with the Intestine). Thanks to this mechanism, most people can take any food without suffering allergic manifestations.
When we eat, the food reaches the stomach and begins to be digested , especially in its protein fraction ; the digestion of protein food is completed in the intestine, with the release of oligo-peptides and individual amino acidswhich will then be absorbed at the mucosal level (see microvilli) and used with a plastic function. However, it may happen that some protein fragments not completely digested, therefore with a medium-high molecular weight , are absorbed by the intestinal mucosa . If these fragments contain an epitope sequence, that is a series of amino acids linked together to form a protein chain recognized as foreign, they can cause sensitization and, if the food is consumed a second time, cause the appearance of those symptomatological manifestations typically associated with food allergy. All this normally does not happen because it is at the level of the mucosaintestinal there are secretory immunoglobulins A (IgAs), which neutralize these protein fragments preventing them from reaching the systemic level and carrying out their allergenic potential. This mechanism is called tolerance.

In the presence of damage to the intestinal mucosa (gastrointestinal pathologies of inflammatory origin, infections, malabsorption, etc.), insufficient digestive action of proteolytic enzymes or weakening of the immune system, high molecular weight protein fragments can escape this outpost and reach the systemic level, stimulating the synthesis of type E immunoglobulins . In this case there is a first sensitization, which will be followed by real allergic reactions in conjunction with future food intake


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