S498 Observational Studies of Usual Dietary Intake Among Patients with Irritable Bowel Syndrome: A Quality Assessment

Introduction: Irritable bowel syndrome (IBS) is a common gastrointestinal disorder defined by recurrent abdominal pain and altered bowel habits. Diet and food intake are frequently linked to IBS symptoms. Observational studies have assessed dietary intake in patients with IBS. However, the quality of the existing research has not been rigorously examined. We aimed to perform a critical assessment of diet-based studies in IBS to appraise the strength of the body of evidence on diet quality in IBS. Methods: Scopus, Cochrane, CINAHL, EMBASE, and MEDLINE were searched through January, 2021 for randomized controlled trials and observational studies measuring usual diet at baseline (exposure history) in adults with IBS (outcome). Fifty-five studies were identified, published between 1979 and 2021 (Table). Randomized trials that measured baseline diet in all participants prior to study intervention were assessed as observational studies. Two reviewers (RA and GC) independently assessed each study and determined quality as low, moderate, or high using the Newcastle Ottawa scale (NOS) or NIH quality assessment tools, based on study design. Disagreements were discussed and resolved. Inter-rater reliability was evaluated using the kappa statistic. Reviewer (RA) separately assessed cohort without comparator studies using a modified NOS; kappa statistic was calculated to assess intra-rater agreement between the two tools (NIH and NOS). Results: Among 12,980 unique articles identified, 55 studies were included; 29 studies were classified as case-control and 26 as cohort studies (Table). Cohort studies were further classified as cohorts with (N = 2) and without (N = 24) comparators to determine the optimal assessment tool. Study quality was rated as low, moderate and high for 15, 23 and 18 studies, respectively. The kappa statistic for the concordance between reviewers was calculated at 0.755 (standard error = 0.074 and 95% confidence interval: 0.610 to 0.900). The kappa statistic for concordance between methods used to assess cohort without comparator studies was calculated at 0.692 (standard error = 0.129 and 95% confidence interval: 0.439 to 0.946). Conclusion: Using available tools to appraise the methodological rigor of observational research, we found that most observational studies examining baseline diet in IBS are of moderate to high quality.Table 1.: Quality Assessment of Included Studies; NHLBI = National Heart, Lung, and Blood Institute; NOS = Newcastle-Ottawa Scale.Table 1.: Baseline Characteristics There was no difference in baseline characteristics for subjects who had a decrease in CH4 compared to those who had an increase in CH4 from visit 1 to visit 5.

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