Twenty patients undergoing uneventful gastrectomy were randomly assigned to receive TPN containing either 10% Intralipid or 10% Lipofundin (MCT/LCT) beginning postoperative day (POD) 1 through POD 6. Patients were given non-protein energy 27 kcal/kg/d and nitrogen 0.14 g/kg/d through peripheral vein along with fat emulsion. Body weight, hemoglobin, blood lymphocyte count, SGPT, serum bilirubin, AKP, BUN, Cr, serum albumin, transferrin, prealbumin, fibronectin, creatine phosphokinase, serum and plasma cholesterol, triglycerides, plasma free fatty acids, blood sugar, serum insulin, urinary creatinine and nitrogen balance were monitored. It was found that MCT-based fat emulsion was tolerated without any side effects. Kinetics study showed that levels of medium chain free fatty acids increased during MCT-based fat emulsion infusion, but returned to normal within 2 hours on cessation of infusion, indicating good clearance of MCT. Plasma concentration of triglycerides in the LCT group was higher than that in the MCT group at 2 hours after infusion. On POD 6, better nitrogen balance was observed in the MCT group, 0.44 +/- 0.21 g/d (-1.4 +/- 0.51 g/d in the LCT group). Urinary excretion of creatinine in the MCT group was also less than in the LCT group (0.76 +/- 0.03 g/d vs. 1.034 +/- 0.11 g/d). LCT was also observed to induce an elevation of serum bilirubin (1.12 +/- 0.11 mg/dl). These results indicate that MCT-based fat emulsion appears to be a safe energy source.