The human gut hosts more than 100 trillion microorganisms, encompassing thousands of species. In adults, Bacteroidetes and Firmicutes are the most prevalent phyla. Experimental data in animal and observational studies in obese patients suggest that obesity is associated with substantial changes in the composition and metabolic function of the gut microbiota. The initial findings linked obesity with the decreased relative proportion of Bacteroidetes to Firmicutes. There are some authors who suggest that probiotics and prebiotics can modulate obesity-host metabolism in obesity and obesity-related disorders.