Background: Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder with a multifactorial etiology in which dietary pattern, including fiber intake and fermentable carbohydrate consumption, has been increasingly implicated as a modifiable contributing factor.

Objective: This simulated case-control study examines the association between habitual dietary fiber intake, high fermentable oligosaccharide-disaccharide-monosaccharide-and-polyol (FODMAP) consumption, and risk of IBS among adult gastroenterology outpatients.

Method: A hypothetical case-control design was used, comparing 160 simulated Rome IV-diagnosed IBS cases with 160 simulated symptom-free controls, matched for age and sex. Simulated data on daily dietary fiber intake, high-FODMAP food consumption frequency, psychological stress score, and bowel habit subtype were analyzed using descriptive statistics, chi-square tests, and binary logistic regression.

Results: In this simulated dataset, cases reported lower mean daily fiber intake (14.2 ± 5.1 g) than controls (21.6 ± 6.3 g) and higher frequency of high-FODMAP food consumption. Logistic regression suggested low fiber intake (<18 g/day) was associated with elevated odds of IBS (simulated OR = 2.18, 95% CI: 1.41–3.37, p < 0.001), and frequent high-FODMAP consumption was independently associated with increased odds (simulated OR = 2.46, 95% CI: 1.58–3.83, p < 0.001), after adjustment for psychological stress score and body mass index.