Background -Irritable bowel syndrome (IBS) is a chronic functional condition, which main symptoms of pain, discomfort and abdominal distension, constipation, diarrhea, altered fecal consistency and sensation of incomplete evacuation can be influenced by the presence of dietary fiber and fermentable carbohydrates (FODMAPs). This study aimed to assess the relationship between the quantity of fermentable carbohydrates (FOD-MAP) and fiber consumed by individuals diagnosed with IBS, and their classification according to the Rome III criteria. Methods -A transversal study was carried out in the Intestinal Outpatient Clinic of the Gastroenterology Discipline of UNIFESP. The nutrients of interest for the study were: fiber, general carbohydrates and FODMAPs, with intake quantity measured in grams, analyzed through portions consumed. A nutrition log was used, along with a semi-quantitative questionnaire of consumption frequency. Results -The sample included 63 adult patients; 21 with constipated IBS, 21 with diarrhea IBS, and 21 with mixed IBS. Carbohydrate intake was suboptimal in 55.6% of patients in all groups; excessive consumption was identified in 38.1% of the diarrhea group, 14.3% of the mixed group and 38.1% of the constipated group. Low consumption of carbohydrates was found in 28.6%of diarrhea patients and 47.6% of the mixed group. A mean intake of 23 g of fiber per day was identified, lower than recommended. Conclusion -The study identified a number of inadequacies in the consumption of different nutrients, excessive carbohydrate intake, especially FODMAPs, identified by the respondents as responsible for a worsening of their conditions. By contrast, other food groups such as meat, eggs and dairy were consumed by the sample population in insufficient quantities.