The rate of gastric emptying is known to be a control point in the digestive process because most food present in the gastrointestinal tract prior to the pyloric sphincter is not able to be absorbed. Only after the food enters the duodenum does mass absorption begin, and therefore the length of time the food is present in the stomach has great implications on the rate at which the food enters circulation. In addition, one of the limiting factors on further food intake is the distension of the stomach. Therefore delaying the transit of food through the gut by holding it in the stomach not only decreases the speed of absorption but also has a significant effect on satiety. However, research has shown that the stomach is able to regulate gastric emptying to maintain a constant flow of nutrients to the duodenum, presumably because this ensures adequate nutrient absorption from food.
For example, researchers1 have investigated the effects of the energy density of food on gastric emptying and satiety in nine healthy subjects. Subjects were fed either a dilute or concentrated liquid meal containing 597.5kcal with 80% as solids. The dilute meal had 638.4kcal/L in 950mL and the concentrated meal had 1781.1kcal/L in 350mL. The results showed that the solid and liquid component of the meals were not significantly different in their half-emptying times from the stomach. Further, the pyloric throughput was not significantly different between the two test meals and was not therefore affected by the energy density of the food. The gastric emptying time was calculated as 2kcal for the first 3 hours postprandially, but thereafter decreased. Because the energy throughput was not significantly different, the pyloric output of meal volume was significantly greater for the dilute meal.
The authors used a visual analogue scale to rate satiety, with subjects reporting a decrease in satiety over time postprandially with both meals. Satiety was highest during the first two hours and fell after that point. However, there was no significant difference between the satiety rating for the two meals. Ad libitum energy ingestion in the subsequent 6 hours following the test meals was similar between subjects further suggesting no difference in the satiety caused by the dilute or the concentrated meal. These results tend to suggest that the stomach is able to increase or decrease the throughput of energy past the pyloric sphincter in relation to the energy contained within the meal, thus supplying the duodenum with ≈2kcal/min. This evidence is supported by research showing that food present in the duodenum prevents gastric emptying, thus maintaining constant rates of total energy for absorption across the intestinal mucosa.
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