A study by Gualberto et al. [31] indicates that changes in the content of SDF and IDF depend on the type of the cereal raw material. Those authors showed no effect of extrusion on the content of dietary fiber of wheat bran, while in case of oat and rice bran they found a slight decrease in the content of the IDF fraction and an increase in the content of the SDF fraction. An increase in the content of dietary fiber, mainly the lignin fraction, may be related to Maillard’s reaction products being formed during thermal processing, which in the Van Soest method are determined as the lignin fraction [32]. A similar trend was also observed by Valiente et al. [33], and Dziedzic et al. [8].