BACKGROUND AND AIM: The gut microbiota in irritable bowel syndrome (IBS) is known to vary with diet. We aim to (i) analyze the gut microbiota composition of IBS patients from a multi-ethnic population and (ii) explore the impact of a low FODMAP diet on gastrointestinal symptoms and gut microbiota composition among IBS patients. METHODS: A multi-center study of multi-ethnic Asian patients with IBS was conducted in two phases: (i) an initial cross-sectional gut microbiota composition study of IBS patients and healthy controls, followed by (ii) a single-arm 6-week dietary interventional study of the IBS patients alone, exploring clinical and gut microbiota changes. RESULTS: A total of 34 adult IBS patients (IBS sub-types of IBS-D 44.1%, IBS-C 32.4%, and IBS-M 23.5%) and 15 healthy controls were recruited. A greater abundance of Parabacteroides species with lower levels of bacterial fermenters and short-chain fatty acids producers were found among IBS patients compared with healthy controls. Age and ethnicity were found to be associated with gut microbiota composition. Following a low FODMAP dietary intervention, symptom and quality of life improvement were observed in 24 (70.6%) IBS patients. Symptom improvement was associated with adherence to the low FODMAP diet (46.7% poor adherence vs 92.9% good adherence, P = 0.014), and gut microbiota patterns, particularly with a greater abundance of Bifidobacterium longum, Anaerotignum propionicum, and Blautia species post-intervention. CONCLUSION: Gut microbiota variation in multi-ethnic IBS patients may be related to dietary intake and may be helpful to identify patients who are likely to respond to a low FODMAP diet.