Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by abdominal pain associated with defecation, or changes in stool frequency or stool form . The low FODMAPs diet (LFD) is a relatively new approach in the management of IBS and focuses on limiting intake of poorly absorbed carbohydrates. FODMAPs are highly fermentable but poorly absorbed short-chain carbohydrates and polyols contained in a wide variety of foods. FODMAPs include oligosaccharides (fructans, fructo-oligosaccharides = FOS and galacto-oligosaccharides = GOS), disaccharides (lactose), monosaccharides (fructose), and polyols (sorbitol, mannitol, maltitol, xylitol, polydextrose, and isomalt). Many studies and meta-analysis in adults have shown that a low FODMAPs diet is effective in reducing IBS symptoms, particularly bloating and abdominal pain. On the other hand, evidences in children are scarce. Previous studies in adults have demonstrated differences in urine metabolites between IBS patients receiving LFD compared to a high FODMAP diet (HFD), providing interesting hypotheses for pathophysiological mechanisms in IBS. Aim of this study is to evaluate the efficacy of a LFD on gastrointestinal symptoms in children with IBS. Moreover, the investigators will assess the impact of LFD vs a diet with a standard content of FODMAPs (SFD) on the fecal and urinary metabolomic profile of pediatric IBS patients. This is a single center, prospective, single blind low versus standard FODMAPs diet trial with crossover performed at Pediatric Gastroenterology Unit at the University of Bari. The trial includes four phases (run-in, low FODMAP diet, wash out and standard FODMAP diet). The run-in phase (weeks 1-2) aim to assess basal symptoms while on habitual diet and only symptomatic children (VAS\>3) will progress to the dietetic intervention trial. Then patients will be randomized to low or standard FODMAP diet for 14 days; then, children from both arms start the wash-out period of two weeks and subsequently start the final 2-week period on standard or low FODMAP diet.