Conscious young adult male rats were given total parenteral nutrition (TPN) with or without soybean fat for 4 days. Those given fat-free TPN developed severe fatty liver, with hyperglycaemia, hyperinsulinaemia, and hypotriglyceridaemia. These disorders were clearly improved by supplementing TPN with soybean fat, in an amount equivalent to 20% of total calories, and correspondingly reducing glucose. Insulin resistance also developed over a 4-day infusion of fat-free TPN in mature rats. Even after over-night fasting after stopping the TPN infusion, the levels of serum glucose and insulin were higher in the fat-free TPN group than in the control group, and intravenous glucose tolerance test results indicated insulin resistance in the fat-free TPN group. The HOMA-IR index of insulin resistance was significantly improved by supplementation with soybean fat. In conclusion, fat-free TPN infusion induced hyperglycaemia and hyperinsulinaemia, leading to fatty liver and insulin resistance. TPN with glucose should be supplemented with soybean fat emulsion as replacement for part of the glucose calories.