Materials & Methods: In this cross-sectional study, data on 3846 Iranian general adults working in 50 different health centers were examined. Dietary intake of the participants was assessed using a 106-item self-administered Dish-based Semi-quantitative Food Frequency Question-naire (DS-FFQ) which was designed and validated specifically for Iranian adults. A modified Persian version of the Rome III questionnaire was used for assessment of FGIDs, including IBS, which was defined according to ROME III criteria. To identify major dietary patterns based on the 39 food groups, we used principal component analysis.

 Results: We identified four major dietary patterns: 1) “fast food” dietary pattern 2) “tradi-tional” dietary pattern 3) “lacto-vegetarian” dietary pattern 4) “western” dietary pattern. Af-ter adjustment for potential confounders, we found that those in the highest quartile of “fast food” dietary pattern tended to have higher risk of IBS than those in the lowest quartile (1.32 0.99, 1.75, Ptrend=0.05). An inverse association was found between “lacto-vegetarian” die-tary pattern and risk of IBS such that even after adjustment for potential confounders, those in top quartile of this dietary pattern were 24% less likely to have IBS (0.76 0.59, 0.98 Ptrend=0.02). No overall significant associations were observed between “traditional” and “western” dietary patterns and risk of IBS, either before or after adjustment for covariates. 

Conclusion: We found that “lacto-vegetarian” dietary pattern was associated with reduced risk , while “fast food” dietary pattern was associated with a greater risk of IBS in Iranian adults.