Objective:To explore the correlation between dietary fiber intake and intestinal barrier function in patients with irritable bowel syndrome with diarrhea (IBS-D).Methods:IBS-D patients were recruited from May 2019 to October 2019 at the clinic of gastroenterology department in China-Japan Friendship Hospital and healthy controls (HCs) were recruited by advertisement. Clinical manifestations, psychological status and quality of life were assessed using standardized questionnaires. A food frequency questionnaire was used to assess dietary habits in the preceding year. Serum diamine oxidase (DAO) was measured via ELISA.Results:64 IBS-D patients and 35 HCs were enrolled, with no significant difference in sex ratio, age and BMI between the two groups. Second to health concern, food avoidance was the dominant impacting factor for quality of life in IBS-D patients. The intake frequency of dietary fiber was decreased in IBS-D patients, and the intake frequencies of dietary fiber-rich foods were significantly lower in IBS-D patients ( P < 0.01 for tubers, P = 0.002 for vegetables, P = 0.019 for fruits and P = 0.045 for legumes). On the other hand, the intake frequencies of processed meat ( P < 0.01), greasy food ( P = 0.009), barbecued food ( P = 0.002) and animal offal ( P = 0.003) were significantly higher in IBS-D patients compared with HCs, indicating the increased intake frequency of fat. Multivariate logistic regression showed that tubers might reduce the risk of IBS-D ( OR = 0.409,95% CI: 0.232 to 0.722, P = 0.002). The frequency of abdominal pain was positively associated with the intake frequency of greasy food in IBS-D patients. Serum DAO was measured in 37 IBS-D patients and 27 HCs. IBS-D patients had significantly higher serum DAO than HCs ( 77.0 [55.3, 100.6] μg/L vs 42.5 [28.0, 58.2] μg/L, P < 0.01). Among all the participants with serum DAO test results, the level of DAO was negatively associated with the intake frequencies of tubers, vegetables and fruits while positively associated with the intake frequencies of processed meat and barbecued food. Conclusions:Food avoidance was an important impacting factor for quality of life in IBS-D patients. IBS-D patients might have insufficient dietary fiber intake and excessive fat intake. Tubers could possibly reduce the risk of IBS-D. The decreased intake frequency of dietary fiber might have a role in intestinal barrier dysfunction in IBS-D patients.