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We compared anxiety, neuromotor, and cognitive functions in mutant rats with different allelic variants of dopamine transporter DAT knockout receiving balanced or excess in fat and fructose diet. The experiments were performed in DAT−/− homozygotes, DAT+/− heterozygotes, and DAT+/+ wild type rats. The genotype of DAT‐KO rats was confirmed by restriction analysis of DAT gene compared to behavioral responses in the open field test (OF). Animals in the first groups of each strain were fed a balanced AIN93M diet; and those in the second groups with a high‐fat/high‐fructose diet. Neuromotor function was studied as grip strength, and behavioral responses were assessed in the elevated plus maze and conditioned passive avoidance response tests. The mass of the internal organs and white and brown fat, as well as selected lipid and nitrogen metabolism parameters in blood plasma were determined at the end of the experiment. DAT−/− had the highest specific grip strength, and showed an increase in initial exploratory activity in comparison with DAT+/− and DAT +/+. The exploratory activity was significantly reduced in the second test compared to the first one in DAT−/− and DAT+/− of first but not second group. Anxiety decreased with age in the second groups of DAT+/− and DAT+/+ (but not in DAT−/−) and was higher in DAT+/+ than in DAT+/− and DAT−/−. Excess fat and fructose resulted in the deterioration of short‐term memory in DAT+/+. Lipidomic indices of blood plasma were less responsive to diet in DAT−/− and DAT−/+ in comparison to DAT+/+. The increased AsAT/AlAT activity ratio in DAT−/− compared with those in DAT+/+ suggests the activation of catabolism activity in the mutants. The consumption of excess fat and fructose significantly modified the effects produced by DAT gene allelic variants presumably due to the influence on the processes of dopamine metabolism.