AIM: To investigate whether composite yogurt with acacia dietary fiber and Bifidobacterium lactis (B. lactis) has additive effects in irritable bowel syndrome (IBS). METHODS: A total of 130 patients were randomly allocated to consume, twice daily for 8 wk, either the composite yogurt or the control product. The composite yogurt contained acacia dietary fiber and high-dose B. lactis together with two classic yogurt starter cultures. Patients were evaluated using the visual analogscale via a structured questionnaire administered at baseline and after treatment. RESULTS: Improvements in bowel habit satisfaction and overall IBS symptoms from baseline were significantly higher in the test group than in the control group (27.16 vs 15.51, P = 0.010, 64.2 ± 17.0 vs 50.4 ± 20.5, P < 0.001; respectively). In constipation-predominant IBS, improvement in overall IBS symptoms was significantly higher in the test group than in the control group (72.4 ± 18.4 vs 50.0 ± 21.8, P < 0.001). In patients with diarrhea-predominant IBS, improvement in bowel habit satisfaction from baseline was significantly higher in the test group than in the control group (32.90 vs 7.81, P = 0.006). CONCLUSION: Our data suggest that composite yogurt enriched with acacia fiber and B. lactis has greater therapeutic effects in patients with IBS than standard yogurt. AIM: To investigate whether composite yogurt with acacia dietary fiber and Bifidobacterium lactis (B. lactis) has additive effects in irritable bowel syndrome (IBS). METHODS: A total of 130 patients were randomly allocated to consume, twice daily for 8 wk, either the composite yogurt or the control product. The composite yogurt contained acacia dietary fiber and high-dose B. lactis together with two classic yogurt starter cultures. Patients were using the visual analog scale via a structured questionnaire administered at baseline and after treatment. RESULTS: Improvements in bowel habit and overall IBS symptoms from baseline were significantly higher in the test group than in the control group (27.16 vs 15.51, P = 0.010, 64.2 ± 17.0 vs. 50.4 ± 20.5, P <0.001; respectively). In constipation- predominant IBS, improvement in overall IBS symptoms was significantly higher in the test group than in the control group (72.4 ± 18.4 vs 50.0 ± 21.8, P <0.001). In patient s with diarrhea-predominant IBS, improvement in bowel habit preference from baseline was significantly higher in the test group than in the control group (32.90 vs 7.81, P = 0.006). CONCLUSION: Our data suggest that composite yogurt enriched with acacia fiber and B lactis has greater therapeutic effects in patients with IBS than standard yogurt.