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SUMMARY Food intake and feelings of hunger and fullness were monitored in paired studies carried out in two groups of six healthy non-obese male volunteers during infusion of isotonic solutions of either a 50% corn oil emulsion or saline into the jejunum or into the ileum. Infusion of the lipid emulsion at a rate of 1-2 ml/min (4.9 kcal/min) into either the ileum or the jejunum significantly reduced the period of eating (p<0-01) and the quantity of food consumed (p<0O01), but neither affected the rates of drinking or the amount of fluid consumed. Infusion of the lipid emulsion into the jejunum also significantly reduced the sensations of hunger before the meal (p<005), and the rate of ingestion (p<0-01). Ileal infusion did not influence these indices. The results suggest that jejunal and ileal infusion of lipid reduces the size of the meal that could be consumed possibly by inhibiting gastric emptying. The alleviation of hunger before ingestion and the slower rate of eating, however, suggests that jejunal lipid activates an additional mechanism that influences the appetite centre in the hypothalamus directly.The mechanisms that regulate food intake and satiety in man are poorly understood, though on the basis of experiments carried out in rats, it has been suggested that food intake may be terminated by stimulation of nutrient receptors within the gastrointestinal tract.' In support of this hypothesis we have previously observed that infusion of lipid emulsion into the ileum reduced the amount of a meal consumed by normal volunteers2 whereas intravenous infusion of a similar lipid emulsion did not influence eating behaviour.2 The effect of ileal lipid on satiety is compatible with mediation by changes in gastric volume as it was associated with a delay in gastric emptying2 and a reduction in the capacity for food with no change in the rate of eating. In support of this idea, studies in rats have shown suppression of food intake during distension of the stomach with a balloon.3 It is possible however, that satiety and Address for correspondence: Dr N W Read, Sub-Department of Human Gastrointestinal Physiology and Nutrition, Royal Hallamshire Hospital, Sheffield, S10 2JF.Received for publication 11 September 1987. delayed gastric emptying after ileal infusion of lipid could be mediated by the central nervous system. Experiments in animals, however, suggest that the interaction of nutrients with receptors in the upper small intestine may reduce food intake by an action that is independent of gastric distension. Instillation of nutrients into the duodenum inhibits food intake in rats and monkeys equipped with gastric fistulae and triggers behaviour identical to that which occurs after a meal even though there is no food in the stomach.4T he aim of the study was to investigate possible satiety mechanisms triggered by receptors in the upper small intestine, by comparing the effects of infusion of lipid into the jejunum and ileum of normal human subjects on eating behaviour feelings of hunger and fullness. Methods S...