Intervention: (Weeks 1-2, Visit 3-4) - Starting from the second week after the date of consent, patients with IBS will be randomized 1:1 into two groups. The first group (20 patients) will receive one week of a low FODMAP supplemented with fermented milk followed by one week of a low FODMAP content supplemented with fermented beans. The second group (20 patients) will receive a low FODMAP diet supplemented for one week with fermented beans followed by a second week of a diet with a low FODMAP diet supplemented with fermented milk. The microbiome of the patients will be evaluated after the first and second weeks along with data related to weight. After the second week, the metabolome and physical characteristics. The enrollment period will last for one year. The analysis of clinical data will be completed within one year after patient enrollment. Analysis of laboratory data will be performed in parallel.