Preventive and/or therapeutic agent for inflammatory bowel diseases

A method for treating an inflammatory bowel disease (IBD) comprising administering an effective amount of a fermentation product of a propionic acid bacterium to a subject in need thereof, wherein the fermentation product is a fermented milk whey which comprises 1,4-dihydroxy-2-naphthoic acid (DHNA) and the DHNA content in said fermentation product is equal or less than 0.01 w/w % of the solid content of the fermentation product, and wherein the propionic acid bacterium may be optionally removed after fermentation.