The aim of this work was to study the effects of low energy parenteral diets with different lipid/glucose ratios on rat liver and jejunal mucosa protein synthesis. The studied diets were: LO (100 % glucose, control diet), L25 (25 % lipids: 75 % glucose), L50 (50 % lipids: 50 % glucose) and L75 (75 % lipids: 25 % glucose). All diets were isoenergetic and isonitrogenated, with a standard amino acid content. The diets were assayed in 93 rats with open femoral fracture immobilized by Kirschner pin insertion. The diets were administered for 4 days. On the fifth day, liver and jejunal mucosa protein synthesis were determined. Highest liver protein synthesis rates were obtained with the diet compositions: lipid/carbohydrate ratio: 25 % lipids and 75 % carbohydrates (expressed as energy ratio). A higher proportion of lipids significantly decreases liver protein synthesis (p<0.05). Jejunal mucosa protein synthesis followed the same pattern, with the same statistical differences.