In the pathogenesis of obesity, various factors interact in a very detailed and complex manner: behavioral, psychological, environmental, metabolic, neuro-immune-endocrine.

Several studies have shown a relationship between intestine microbiota and obesity. Even though not univocally, studies that have been carried out in mice and humans have shown a change in the composition of the intestinal microbiota in obese subjects with an increase in Firmicutes and a Bacteroidetes reduction.

Experimental and clinical evidence are illuminating in a surprising manner regarding the complex entity of intestinal microbiota and its multiple functions. It was observed that the microorganisms that colonize the gastrointestinal tract are not only guests nearly inert but are active protagonists of lively interactions between the gastrointestinal tract and the neuro-immune-endocrine system.

The total genome of single intestinal flora is exponentially richer than the human genome genes. In fact we know that the intestinal flora comprises 1014 bacteria to which should be added fungi and viruses. Only 1% of our genes is transmitted from parents, the remaining 99% is acquired by the microbiome present in the surrounding environment in particular at the time of birth, during the passage through the birth canal and then with breastfeeding.