Conflict of interest statement: Danone commissioned York Health Economics Consortium (YHEC) Ltd. (an independent research organization) and Quantics Consulting (a statistical consultancy) to carry out this systematic review and meta-analysis. Dr Jacqui Eales (YHEC) served as a researcher on this review. Dr Eales has previously received funding from Danone Institute International (DII) to deliver a conference presentation of the outcome of another systematic review commissioned by DII and undertaken by YHEC. Dr Peter Gibson has served as a consultant or advisory board member for Abbvie, Ferring, Janssen, Merck, Nestle Health Science, Danone, Allergan and Takeda. His institution has received speaking honoraria from Abbvie, Janssen, Ferring, Takeda, Fresenius Kabi and Pfizer. He has received research grants for investigator-driven studies from Abbvie, Janssen, Falk Pharma, Danone and A2 Milk Company. His department financially benefits from the sales of a digital application and booklets on the low FODMAP diet. He has published an educational/recipe book on diet. Dr Peter Whorwell has acted as a consultant for, or received research grant support from, the following companies in the last 5 years: Almirall Pharma, Boehringer-Ingelheim, Chr. Hansen, Danone Research, Ironwood Pharmaceuticals, Salix, Shire UK, Sucampo Pharmaceuticals and Allergan. Dr John Kellow is a Board member of the Rome Foundation and is on the Advisory Board of Danone Australia. Dr Ann Yellowlees is a Director of Quantics, and declares no additional personal interests. Dr Richard Perry (Quantics) declares no additional personal interests. Mary Edwards, Dr Sarah King, Hannah Wood and Julie Glanville are employed by YHEC, and declare no additional personal interests.