Food Allergies: Causes and Risk Factors

Although many people experience adverse reactions to certain foods , actual allergic diseases are less common than you might think. Despite this, the number of people suffering from food allergies continues to increase. An important problem, therefore, which currently affects approximately 2-7% of adults and 6-13% of children.
The incidence of food intolerances appears to be much higher ( lactose intolerance , for example, reaches values ​​above 90% in some ethnic groups), but as we have had the opportunity to repeat on several occasions, they must 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?

Inheritance

Atopy , i.e. the genetic predisposition to develop allergic reactions due to ingestion or inhalation of allergens, is more frequent in families with allergic subjects. This does not mean that food allergies are passed 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 varies between 47 and 100%, compared to 13% for children without a family history.
However, this inheritance presents some peculiar characteristics:

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

Antigen exposure

Every time the organism comes into contact with an antigen, therefore with a protein that is not its own, it produces antibodies against it. Theoretically, therefore, our body should react and develop antibodies towards all food proteins , as food represents our most intimate contact with the external environment. This, fortunately, happens with pathogens but not with foods, because the immune system recognizes food proteins as foreign but harmless substances, thanks to a mechanism, defined 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, precisely, Lymphoid Tissue Associated with the Intestine). Thanks to this mechanism, the majority of people can eat any food without suffering allergic reactions.
When we eat, the food reaches the stomach and begins to be digested , especially in its protein fraction ; the digestion of food proteins is completed at the intestinal level, with the release of oligopeptides and individual amino acids which will then be absorbed at the mucosal level (see microvilli) and used with a plastic function. However, it may happen that some protein fragments that are not completely digested, therefore with a medium-high molecular weight , are absorbed by the intestinal mucosa . If these fragments contain an epitopic sequence, i.e. 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 symptomatic manifestations typically associated with food allergy. This does not normally happen because at the level of the intestinal mucosa there are secretory immunoglobulins A (IgAs), which neutralize these protein fragments, preventing them from reaching the systemic level and fulfilling 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 the proteolytic enzymes or debilitation of the immune system, high molecular weight protein fragments can escape this outpost and reach a systemic level, stimulating the synthesis of type E immunoglobulins . In this case there is an initial sensitisation, which will be followed by actual allergic reactions in conjunction with future intakes of the food.