Adaptation to high-fat diet accelerates emptying of fat but not carbohydrate test meals in humans.

Previous work has shown that the gastric emptying rate in animals and humans can adapt due to previous dietary intake. The present study investigated whether adaptation in gastric emptying rate due to consumption of a high-fat diet (HFD) is nutrient specific in humans. Gastric emptying of high-fat and high-carbohydrate test meals was measured (using gamma scintigraphy) before and after consumption of an HFD for 14 days in eight free-living male volunteers. Visual analog ratings of appetite were recorded throughout each test. There was no effect of HFD on any parameters of gastric emptying rate (lag phase, half-emptying time, and linear emptying rate) measured for carbohydrate test meals. HFD led to an acceleration of the linear emptying rate of the high-fat test meal (0.36 vs. 0.47%/min; P < 0.05). All meals reduced appetite ratings, but there were no differences between tests. These results support our previous findings of accelerated gastric emptying of high-fat test meals following an HFD and show that these changes appear to be nutrient specific, confirming recent studies in rats.

Food intake responses to upper gastrointestinal lipid infusions in humans.

Previous studies in humans and animals have shown that the presence of lipid in the small intestine can reduce food intake. Studies that have combined intraduodenal lipid infusions with gastric distension produced a greater reduction in food intake than when these two stimuli were separated. In this study, subjects received duodenal lipid (Intralipid 20%) infusions for varying periods before and during the consumption of a liquid test meal. The aim of this procedure was to maximise the interaction between intestinal nutrient stimulation and gastric distension. A dose-dependent decrease in food intake was observed that corresponded to the duration of infusion; 90- (180 kcal) and 45-min (90 kcal) infusions but not 15-min (30 kcal) infusions significantly reduced intake compared to saline. These results show that concomitant intestinal nutrient stimulation and gastric distension is an effective test for the measurement of suppression of food intake by intestinal nutrients.

Effects of intragastric infusions of fat and carbohydrate on appetite ratings and food intake from a test meal.

Previous studies using meal preloads have indicated that carbohydrate has a greater satiating power than fat. To investigate the effects of macronutrients on ingestion and satiety, without the influence of meal design and orosensory factors, two groups of ten healthy, fasted male volunteers took part in two separate experiments involving rapid direct intragastric infusions of macronutrients. In the first experiment volunteers received isocaloric infusions of either Intralipid, or 1:1 Intralipid and glucose mixture or saline over 15 min on three separate occasions. In a second experiment volunteers received isocaloric infusions of either Intralipid or glucose. For both studies, appetite ratings were recorded for the first two hours of the study and energy and macronutrient intakes were evaluated from a test meal given 1.5 h after the infusion. Food diaries were used to monitor food intake for the remainder of the study day. In the first experiment, both Intralipid and the Intralipid/glucose mixture suppressed appetite ratings and reduced energy intake at lunch compared with saline but had no effect on energy intake during the remainder of the study day. No differences were found between nutrient conditions in suppressing appetite ratings or energy intake. In the second experiment there were no differences between the effects of Intralipid and glucose on hunger, fullness or on energy intake from the test meal or intake over the remainder of the day. Taken together, these results suggest that intragastric infusions of either Intralipid, glucose or a mixture of the two, reduced hunger and increased fullness, but they failed to confirm the hypothesis that different macronutrients have different satiating capacities.