Aim: Protein-energy malnutrition is frequently observed in patients with liver cirrhosis (LC). Non-protein respiratory quotient (npRQ) measured by indirect calorimetry is a good marker to estimate energy malnutrition, and predicts the prognosis of patients with LC. However, measurement of npRQ is limited because of the high cost of indirect calorimetry. Our aim was to find out an alternative marker to npRQ that can be used in the routine clinical setting. Methods: One hundred and fifty-six patients with LC were enrolled in this study. Indirect calorimetry and blood examinations were conducted after overnight fasting, and anthropometry was performed by an expert dietician. The correlation between npRQ and other parameters were calculated by simple and multiple regression analysis. Receiver-operator curve (ROC) analysis was used to identify the cut-off value that would best predict the threshold npRQ of 0.85. Results: Plasma levels of free fatty acid (FFA) was significantly correlated with npRQ value by simple (r=-0.39, P<0.0001) and multiple regression analysis (t=-2.96, P=0.0052). Free fatty acid rose in parallel with the increasing disease severity as defined by Child-Pugh classification (P<0.05). FFA was also correlated with increasing oxidation rate of fat (r=0.38, P<0.0001) and decreasing oxidation rate of carbohydrate (r=-0.39, P<0.0001). The cut-off value of FFA to predict npRQ=0.85 was 660μEq/L by ROC analysis. Conclusion: FFA is a useful alternative marker to represent npRQ in patients with LC. © 2013 The Japan Society of Hepatology.