Abstract The influence of dietary protein, lipid and carbohydrate proportions on liver glutamate dehydrogenase (GDH), fructose 1,6-bisphosphatase (FBPase), glucose-6-phosphate dehydrogenase (G6PDH) and pyruvate kinase (PK) activities was investigated in the European eel (Anguilla anguilla). The highest weight-gain (%) and feed-efficiency indices were obtained using diets with the highest energy content and, for the same energetic content, those with the greatest carbohydrate level. GDH activity increased in fish fed diets with the highest protein: energy ratio with respect to diets either with lower protein or with higher total energy contents. FBPase showed an increased activity in the liver of fish fed on diets with the lowest carbohydrate content and the highest total lipids concentrations. G6PDH activity correlated positively with dietary carbohydrate concentrations and negatively with dietary lipids levels. The increase of carbohydrates and energy levels in the diet increased liver PK activity. In general terms, the European eel showed a certain capacity to adapt intermediary metabolism to changes in diet composition. Amino acid catabolism increased in response to a higher dietary protein: energy ratio. High carbohydrate levels enhanced glucose utilization to yield energy and lipid formation. Gluconeogenesis increased in response to a lower dietary carbohydrate content. High dietary lipid concentrations reduced gluconeogenesis and lipogenesis from carbohydrates.