The paper presents studies of the features of transamination of leucine in skeletal muscles of rats under conditions of nutrient imbalance in the diet. The distribution of the content of free leucine in muscles and blood plasma, the activity of leucine aminotransferase in muscles under conditions of consumption of excessive sucrose content, lack of dietary protein and the combined effect of two dietary factors were studied. During the experiment, experimental animals consumed a semi-synthetic AIN-93 diet in accordance with the recommendations of the American Institute of Nutrition. For the purpose of simulating alimentary protein deprivation, the animals received a semi-synthetic low-protein diet containing 1/3 of the generally accepted daily protein requirement daily for 28 days. A high-sucrose diet was simulated by increasing the amount of sucrose in the diet by 4 times. The content of leucine in skeletal muscles and blood plasma was determined by the method of chromatographic analysis on an automatic amino acid analyzer T 339. Leucine aminotransferase activity in the mitochondrial fraction of skeletal muscles of rats was assessed by the amount of α-ketoisocaproate formed. A significant decrease in leucine content in skeletal muscle of protein-deficient rats was found by 42% and by approximately 70% in groups of animals that received excessive amounts of sucrose compared to the values of control animals. Since the excessive consumption of sucrose leads to a maximum decrease in the level of this amino acid in the muscles of animals, this can be considered as one of the mechanisms of disruption of the supply of glucose to insulin-dependent tissues. At the same time, a 40% decrease in leucine aminotransferase activity was recorded in the skeletal muscles of protein-deficient rats; when consuming a high-sucrose diet, the activity of the studied enzyme is reduced by 50% compared to control indicators. The research results show a decrease in the concentration of leucine in the blood plasma of all experimental groups of animals compared to control indicators. The lowest values of the level of this amino acid were recorded under conditions of consumption of an excess amount of sucrose, regardless of the protein content in the diet. Nutrient imbalance in the diet is accompanied by a violation of leucine transamination processes in the skeletal muscles of rats, which is characterized by a decrease in leucine aminotransferase activity in the mitochondrial fraction, and is obviously associated with a decrease in the content of leucine, the substrate of this reaction. Excessive consumption of sucrose is a key factor in reducing the content of leucine in the blood plasma of rats, which can be considered as a characteristic of the intracellular deficiency of this amino acid in muscles.