Isolated perfuscd livers from fasted rats have been extensively studied to understand the underlying mechanisms of injury induced acute and chronic changes in liver metabolism In this study we investigated the impact of fasting on perfused liver metabolism The methodology we used combines a flux variability approach, sampling analysis and singular value decomposition (SVD) to analyze the data wing the same metabolic reaction network for both fed and fasted livers Considering both experimental observations and mathematical analysis, the results show that 2411 fasting results in a limited glucose production from glycogen and up-regulation of gluconeogenic pathway Glutamate metabolism and fatty acid oxidation are also slightly up regulated whereas aspartate metabolism is down-regulated after fasting Moreover, SVD analysis elucidates that glycogen breakdown mainly affects the pentose phosphate path way in fasted state whereas co-occurrence pattern associated with glycogen breakdown and glycolysis observed in flux samples of fed state is dominant In conclusion, this analysis provides a detailed description of the metabolic changes in two different states, considering the entire steady state flux space and dominant flux patterns that capture the system variations within the flux space Biotechnol Bioeng 2010,107 825-835 (C) 2010 Wiley Periodicals Inc