The effects of gastric infusions of fat and carbohydrate on physiological and psychological measures were compared using a within subject design in 9 healthy subjects (6 males). Each subject received isovolaemic rapid gastric infusions of sucrose solution (100% energy carbohydrate), lipid emulsion (100% energy fat, 20% Intralipid), and a non-nutrient control (0.9% saline) in a randomised order. Nutrient infusions were isoenergetic, containing one-third of an individual subject's estimated daily energy requirements (mean, 3227 kJ; range, 2479-3971 kJ). Measures of heart rate (HR), energy expenditure (EE), mood, and sleepiness were collected before the infusions and every 0.5 h for 3.5 h. Mean postingestive HR, EE, and satiation were significantly greater after the nutrient infusions than after the control. Sucrose induced a rapid increase in HR and EE, whereas lipid had a lesser and more delayed effect. Thirty minutes after the gastric infusions, HR and EE were significantly higher after the sucrose than after the lipid and saline. Hedonic tone was greater and tension lower after the saline and sucrose infusions than after the lipid infusion. From 3 to 3.5 h after ingestion, subjects felt significantly more sleepy after the lipid infusion than they did at these times after the saline infusion, and significantly more dreamy after the lipid infusion than they did after the sucrose infusion. In conclusion, the presence of lipid and sucrose in the intestine induces significant and differing physiological and psychological effects, which are independent of cognitive and orosensory influences.