Postprandial hypotension may be influenced by the digestion of fat. The aim of the present study was to evaluate the hypothesis that products of fat digestion mediate the hypotensive response to fat. In part A of the study, nine healthy older subjects were studied on three separate occasions in randomised order. Blood pressure, heart rate (HR), plasma TAG and gastric emptying were measured following the ingestion of equivolaemic drinks: (1) 300 ml of high-fat drink (88 % fat); (2) fat drink mixed with 120 mg orlistat (lipase inhibitor); (3) water (control). In part B of the study, ten healthy older subjects were studied on two separate occasions. Blood pressure, HR, plasma TAG and superior mesenteric artery flow were measured during 90 min intraduodenal infusions of 10 % intralipid (2·7 ml/min), with and without 120 mg orlistat. Oral fat ingestion was associated with decreases in systolic and diastolic blood pressures (both P¼ 0·0001) that were greater when orlistat was co-administered (both P, 0·05), and an increase in HR (P¼0·0001) that was inhibited by orlistat co-administration (P,0·03). Gastric emptying was slowed by oral fat digestion, and orlistat administration inhibited this slowing (P, 0·04). Intraduodenal fat infusion was not associated with changes in blood pressure but increased HR (P,0·0001), an effect attenuated by orlistat (P,0·05). In conclusion, orlistat potentiates the hypotensive response to oral fat in older adults, possibly as a result of faster gastric emptying of fat. The results do not support a role for fat digestion in lowering blood pressure.Key words: Postprandial hypotension: Fat: Cardiovascular function: Elderly Postprandial hypotension (PPH), defined as a decrease in systolic blood pressure (SBP) of $ 20 mmHg within 2 h of the start of a meal (1) , occurs frequently in older adults and can result in significant morbidity, including an increased risk of falls and syncope (1 -3) , coronary events, stroke and increased mortality (4) . One approach to the prevention and treatment of PPH may be to alter the type of food eaten in favour of macronutrients, which minimise the fall in blood pressure. In the elderly, there is some evidence that carbohydrate ingestion reduces postprandial blood pressure more than other macronutrients (1,5) . Reports of the effects of fat ingestion on blood pressure in older subjects have been inconsistent, with some studies finding no fall (6 -9) or an increase (5) or a delayed but similar fall in blood pressure compared with those of carbohydrate ingestion (10) . If fat ingestion has a less pronounced effect on blood pressure than carbohydrate ingestion, an approach to the management of PPH in affected older people may be to increase fat at the expense of carbohydrate in the diet.Digestion of fat and carbohydrate is necessary for the full slowing of gastric emptying, stimulation of gut hormone release and suppression of appetite that follows the ingestion of these macronutrients in food (11,12) . It is not known, however, whether the digestion of ...