Every laboratory analysis aims to obtain results that are compatible with the methodology used. However, various factors can cause different values to be obtained for a given laboratory analysis of the same material (MARTELLI, 2011). Within this context, this book was developed with the aim of verifying the analytical efficiency of some methodologies for determining protein, carbohydrates, fat and insoluble fiber, used at the IF SERTAO-PE, Petrolina campus, which have undergone modifications in relation to the conventional method, due to practical needs, in order to verify the precision and accuracy of their results. In this way, this book will help academics who are looking for yet another reference in terms of precision and accuracy, which are parameters that can and should be frequently tested in laboratory routines.