This is the peer reviewed version of the following article: de Bortoli, N., Ottonello, A., Zerbib, F., Sifrim, D., Gyawali, C. P. and Savarino, E. (2016), Between GERD and NERD: the relevance of weakly acidic reflux. Ann. N.Y. Acad. Sci.. doi:10.1111/nyas.13169, which has been published in final form at http://dx.doi.org/10.1111/nyas.13169. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.