Rats' response to 'stop snacking' signal diminished by high-fat diet

University Park, Pa. -- Rats fed a high-fat diet were less sensitive to a hormonal "stop eating" signal than rats on a low-fat diet when they were given access to a high-calorie, high-fat snack that the animals find yummy, according to a Penn State study.

"When we gave the rats doses of a 'stop eating' hormone, the rats on the low-fat diet significantly suppressed their intake of the snack but not the rats on the high-fat diet," said Mihai Covasa, assistant professor of nutritional sciences and a member of the Penn State Neuroscience Institute who led the study. "These results suggest that a long-term, high-fat diet may actually promote short-term overconsumption of highly palatable foods high in dietary fat by reducing sensitivity to at least one important feedback signal which would ordinarily limit eating."

The results are detailed in the current (August) issue of the Journal of Nutrition in a paper, "Adaptation to a High-Fat Diet Leads to Hyperphagia and Diminished Sensitivity to Cholecystokinin in Rats." The authors are David M. Savastano, who recently earned his master's degree under Covasa's direction, and Covasa.

The "stop eating" hormone used in the study was cholecystokinin or CCK. CCK is released by cells in the small intestine when fat or protein is present. The hormone's release activates nerves that connect the intestine with the brain where the decision to stop eating is made.

Previous studies with human subjects showed that those on a high-fat diet have more CCK in their bloodstream but are less responsive to it. They typically report feeling increased hunger and declining fullness and eat more.

No human study of snacking and CCK has been reported. This study, with rats, is the first to link diminished sensitivity to CCK following exposure to a high-fat diet and overconsumption of a high-calorie, high-fat snack.

In the current study, the rats were given access to the high-calorie, high-fat snack for only three hours a day. The rest of the time they received either low-fat or high-fat rat chow. The high- and low-fat chows were regulated so that they were equivalent in calories and both groups of rats gained weight at the same rate.

Even though the rats on the high fat diet ate, on average 40 percent more of the high-calorie, high-fat snack than the rats on the low-fat diet, they didn't gain extra weight. Rats, unlike humans, cut back on their usual chow when they snack.

"Rats are notorious in compensating for food to maintain a constant body weight," Covasa said. "Although adaptation to the high-fat diet led to overconsumption of the high-calorie, high-fat snack, there was no difference in weight gain between the two groups of rats during the 20 days of testing because the rats compensated by eating less of their maintenance diet."

The study was supported by a Penn State College of Health and Human Development research grant.