A high-fat diet may desensitize you to feeling full, according to researchers at Pennsylvania State University. The study results, published in the August Journal of Nutrition, suggest that the hormone that produces the sensation of satiation—cholecystokinin (CCK)—is rendered less effective by a high-fat diet (2005, vol. 135, no. 8).

“This is the first study suggesting that a high-fat diet can promote overconsumption by reducing sensitivity to the hormones involved with satiety,” says study coauthor David Savastano. In a 20-day period, one group of rats was fed a high-fat diet, while another group was fed a low-fat diet with an equivalent amount of calories. For three hours a day, both groups were given access to a high-fat, high-calorie snack. When researchers administered CCK, the rats in the low-fat group ate less snack than those in the high-fat group, whose subjects ate as much as 40 percent more.

No human study has been done on the relationship between CCK and snacking, but previous studies suggest that humans have increased hunger and a desire to eat more when consuming a high-fat diet.