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Adverse reactions to food and food allergies are now constantly and dramatically increasing. It is estimated that one fifth of the world population suffers from it with different manifestations based on the etiology and severity of the process.

In addition to improved diagnostic skills, this evident trend is more likely linked to the influence of environmental factors.

Several factors related to the current lifestyle including:

- the increase in births from caesarean section

- the reduction of breastfeeding

- early use of antibiotics

- a diet high in fat and low in fiber

-excess of hygiene

-exposure to environmental pollutants

can compromise the normal intestinal microbial flora during the child's development. The newborn would thus find himself devoid of "good bacteria" which normally prepare the immune system to recognize food as harmless and avoid reacting to food allergens ("tolerance").

Tolerance is maintained in physiological conditions by the resident microbial flora through the maintenance of the integrity of the intestinal epithelial barrier and through the regulation of the activity of T lymphocytes, involved in the production of pro-inflammatory interleukins (IL-4, IL13) .

The intestinal microbiota is therefore fully involved in the development of food allergies as its alterations can compromise the functionality of the immune system and influence its response to food allergens. In the presence of a predisposition, intestinal dysbiosis can therefore favor the development of reactions of sensitivity to food (including intolerances) and overt allergies.

This can happen in several ways.

First of all, changes in the permeability of the intestinal barrier during dysbiosis can allow the entry of potentially harmful and poorly tolerated molecules by our body, with immediate activation of inflammation and stimulation of the immune system.

Secondly, an impairment of the normal bacterial flora can reduce "tolerance" to normal antigens present in food, favoring the activation of the immune system even against molecules that are normally tolerated.

Finally, a malfunctioning microbiota can interact directly with food components, increasing their immunogenicity, that is, the ability to stimulate an inflammatory response. This is what happens - for example - if some molecules are not properly digested. In this sense, short-chain fatty acids seem to play a role in patients with food sensitivity.

To evaluate how dysbiosis can affect immune responses to food, clinical studies compared normal mice with mice born and raised under sterile conditions and mice treated with high-dose antibiotics. After exposure to peanut allergens, both sterile mice and mice treated with antibiotics showed a higher production of antibodies against peanuts than mice raised under normal conditions.

Other studies have shown that infants allergic to cow's milk fed a formula enriched with a type of probiotic ( Lactobacillus rhamnosus ) would appear to develop tolerance towards milk more frequently than infants who take a formula free of probiotics.

Finally, several studies have shown differences in the bacterial composition of the feces of children with food allergy and healthy children. In particular, in one study, food allergic children had fewer bacteria belonging to the Clostridiales family. Mice treated with bacteria contained in the feces of food-allergic children developed allergic reactions. Conversely, mice given Clostridiales did not develop food allergy.

The hypothesis is that good bacteria intervene in the stimulation of immune responses mediated by T lymphocytes. Therefore, it seems that the loss of protective intestinal bacteria is a critical factor in the development of food allergies and in the future the manipulation of the microbiota through probiotics. could help prevent or treat food allergies.

Rossana Cannas

Dr. Rossana Cannas