The objective of this study was to compare the effect of a high fat, low carbohydrate enteral feed with a standard isocaloric, isonitrogenous enteral feed on PaCO2 and ventilation time in patients with acute respiratory failure requiring artificial ventilation. 20 clinically stable patients requiring enteral feeding were randomized to either feed in a double-blind fashion. Initial ventilator standard settings were adjusted according to clinical state. Measurements including minute volume and arterial blood gases were made twice daily. Weaning was carried out according to set criteria. During the feeding period, PaCO2 just prior to weaning fell by 16% in the high fat group but increased by 4% in the standard feed group (p = 0.003). The high fat group spent a mean of 62 h less time on the ventilator (p = 0.006). A high fat, low carbohydrate enteral feed appears to be beneficial in patients undergoing artificial ventilation.