The invention is directed to a method for preparing a fermented dough based food product, to a fermented dough based food product, to the use of native potato protein isolate, to a bread improver, and to a dough. The method of the invention comprises preparing a dough which dough comprises which dough comprises a native potato protein isolate, said native potato protein isolate having a protein content of 90% or more based on dry matter as determined from the weight of total Kjeldahl nitrogen multiplied by 6.25. The invention is also directed to a fermented dough based food product obtainable by said method.