In parenteral nutrition (PN), essential fatty acids are provided by soy oil-based fat emulsions, which may exert adverse effects on the immune system and lipid peroxidation. Olive oil -based fat emulsions have been said to prevent these undesired effects. This study compares effects of olive oil - and soy oil -based fat emulsions in 22 patients who underwent abdominal surgery for cancer. The first group (n = 10) received soy oil -based fat emulsion; the second group (n = 10) received olive oil -based fat emulsion. Body temperature, body mass index, (BMI) and biochemical variables were measured on days 0 and 7. There were no differences between the groups with regard to BMI or temperature. On day 7, the first group (compared with day 0) had significant increases in plasma alkaline phosphatase (81.70 +/- 16.03 vs 117.60 +/- 11.1), gamma-glutamyl transferase (39.90 +/- 15.40 vs 137.70 +/- 24.09), and mean body temperature (36.72 degrees C +/- 0.14 degrees C vs 37.20 degrees C +/- 0.17 degrees C) (P < .01).