The structure of fatty acids is a subject to modification in the process of elongation and desaturation, catalyzed by fatty acid elongases and desaturases, respectively. Regulation of gene expression of desaturases and elongases takes place on the stage of gene transcription and is regulated by hormones and different nutrients. Elongases and desaturases are transmembrane enzymes found primarily in the endoplasmic reticulum. The aim of this study was to investigate the dynamic of changes in gene expression of mRNA for elongases 2, 5 and 6 and 5, 6 and 9 desaturases and determine changes in fatty acid composition of total lipids in response to different types of diets, in liver and adipose tissue, as well as changes in lipid profile and glucose concentration in blood serum. Transcripts for elongases and desaturases was investigated using RT-PCR method. In order to determine the fatty acid composition of total lipids gas chromatography was performed. In response to different diet, in liver and adipose tissue results showed differences in expression levels of mRNA for desaturases and elongases and in fatty acid composition. In the liver of animals fed the same diet, varied levels of expression of mRNA for elongases and desaturases as well as a different fatty acid composition were observed in comparison with adipose tissue. In rats’ serum, a lipid profile and glucose level were different depending on the type of diet.