Response of normal and diabetic rats to increasing dietary medium-chain triglyceride content.

Replacing dietary long-chain triglycerides (LCT) with medium-chain triglycerides (MCT) has not previously been shown to produce reliable changes in caloric intake. However, diabetic rats are particularly sensitive to changes in the fat content of their diet, and thus were used for comparison to normal rats in the studies reported below. Rats were fed synthetic diets that contained either corn oil or MCT. Food intake and plasma metabolic fuels were measured as the fat content of the diet was increased from 5 to 15 to 25%. Both normal and diabetic MCT-fed rats adjusted their caloric intake more quickly than LCT-fed rats as the fat content of the diet was increased. The relative preference of MCT- and LCT-fed rats for high and low concentrations of dietary fat was assessed. It was found that both normal and diabetic LCT-fed rats preferred high dietary fat, whereas MCT-fed rats did not. In normal rats, plasma triglycerides and glycerol were decreased and plasma ketones increased by MCT feeding. In diabetic rats, the only effect of MCT feeding was to decrease plasma glycerol and triglycerides. The relative importance of hedonic and metabolic feedback to the rapid caloric regulation of MCT-fed rats is discussed.