Effect of nutrient density and composition of liquid meals on gastric emptying in feeding rats

Rats were fitted with gastric cannulas to determine gastric emptying rates of liquid test meals after a 16-h fast. They were allowed to drink [14C]polyethylene glycol (PEG) Vivonex High Nitrogen elemental diet (VHN) or Intralipid Fat Emulsion (IL) at 0.25, 0.50, and 1.00 kcal/ml under two conditions: drinking to satiety (VHN) or drinking to a constant volume of 15 ml (VHN and IL). Recovery of stomach contents through the cannula at the end of the drinking period allowed determination of rate of emptying. Average gastric emptying rate (ml/min) during a meal was found to vary inversely with the nutrient density of the test meal. However, the caloric emptying rate (kcal/min), as well as the total caloric load delivered to the intestine by the end of the meal, remained constant over the range of nutrient densities tested. The constancy of caloric emptying rate as diet caloric density increased was independent of diet composition, supporting the hypothesis that rate of gastric emptying is determined by caloric density of the diet. When rats were allowed to drink to satiety, caloric intake was not regulated but increased with increasing diet nutrient density, suggesting that control of meal size was independent of regulation of gastric emptying.