Peripheral blood mononuclear cells (PBMCs) are readily accessible biological material and a potential tissue source to discover novel biomarkers of response to environmental exposures including nutrition. We analyzed whether PBMCs could reflect molecular changes that take place in response to different feeding conditions in key organs/tissues involved in energy homeostasis. We studied energy balance-related genes whose expression was altered in normoweight (control) rats and in diet-induced (cafeteria) obese rats in response to ad libitum feeding, 14-h fasting, and 6-h refeeding after fasting, using whole-genome microarray analysis. In PBMCs, the expression of the genes central to energy metabolism was altered by the feeding conditions. The number of affected genes was 75 in the control rats, but only 23 in the cafeteria obese rats. Most of these genes play a role in metabolic pathways regulated by nutritional changes, such as lipid metabolism (the metabolic pathway mainly reflected in blood cells), carbohydrate metabolism, central energy metabolism, respiratory chain/mitochondrial ATPase system, and food intake regulation. Importantly, our results showed a similar behavior to that of the mesenteric white adipose tissue. In conclusion, metabolic adaptations to acute changes in feeding conditions are reflected in the expression of genes central to energy homeostasis in PBMCs of normoweight rats, while response is impaired in cafeteria obese animals. The lower number of genes affected in obese animals indicates impaired nutritional regulation. PBMCs appear as a suitable potential model to characterize metabolic adaptations to food intake and body weight maintenance in experimental animals. These findings may also inform the development of future peripheral tissue models in the emerging field of clinical nutrigenomics.