Subjects with confirmed diagnosis of Irritable Bowel Syndrome will be blinded and randomly assigned to one of two groups, the low FODMAP diet or the conventional IBS diet group. They will be referred to do three hydrogen breath tests prior to diet education. Upon completion, subjects will attend dietitian consultations at Week 0, 6 and 10 for diet assessment, education and reinforcement. At Week 4 and 8, dietitians will telephone patients to check on diet compliance and answer any diet question. Two sets of questionnaires, the IBS Global Improvement Scale and the IBSQOL will be given to patients to complete before each dietitian visit at week 0, 6 and 10. Two sample t-test and Chi square test will be used to test the difference between the two groups and the association between breath tests results and responds to the two diets.

1. Subjects who are interested will be interviewed and screened for IBS with Rome Ⅲ criteria by the principle investigator. Research information will be explained in length and consent form will be signed if they agreed to participate
2. Subjects will be blinded and randomly assigned to Conventional IBS diet group (A) or Low FODMAP diet group (B)
3. 3 Breath tests (lactulose, fructose, lactose) will be carried out for all subjects before diet education
4. Subjects will be asked to come to the dietitians clinic and receive the first one hour diet education (including diet assessment & diet education) and two times thirty minutes follow-up appointments with the dietitians at Week 0, 6 and 10, respectively
5. Subjects will be asked to record their food intake and signs and symptoms onto a food record book
6. Subjects will be asked to fill out the IBS Global Improvement Scale and the IBSQOL questionnaire at Week 0, 6 & 10
7. At week 4 and week 8, telephone interviews will be conducted by the dietitians to reinforce diets and answer diet questions
8. Results of IBS Global Improvement Scale and IBSQOL questionnaire will be analyzed using two sample t-test to test the difference between control and treatment group
9. Chi square test will be used to look at the association between breath tests results and responds to the two diets

Inclusion Criteria:

• Adults >18 years
• Confirmed IBS (after meeting Rome Ⅲ criteria)
• Hong Kong Chinese

Exclusion Criteria:

• Age <18 years
• Pregnancy
• Other ethnicities besides Hong Kong Chinese
• Significant GI co-morbidities such as Inflammatory Bowel Disease, Coeliac disease, significant diverticular disease, history of GI cancer, GI resection and GI reconstruction