High Fat Means High Hunger

Did you know you have a special mechanism in your body that tells you when to put down that fork and stop eating? As soon as your small intestines detect fat or protein, they release a hormone, called cholecystokinin (CCK), which tells your brain you’ve had enough. If we humans are anything like laboratory rats, high-fat diets could cause our bodies to ignore this “stop-eating” hormone, making us more prone to overeating.

In a recent study, researchers observed two groups of rats for 20 days, one on a high-fat diet and the other on a low-fat diet. For three hours each day, they left a bunch of tasty, fatty snacks that rats love close by. The rats on high-fat diets ate as much as 40 percent more than those on low-fat diets. In the second part of the study, the researchers injected all the rats with CCK at noon and then placed food in front of them for an hour.

Because the CCK made them feel full, the rats on the low-fat diet ate much less than usual. However, the rats on the high-fat diets didn’t seem to notice CCK’s effect and kept right on eating. They had had apparently become desensitized to the hormone, say the researchers.

Human studies have shown similar results in the past. For example, in a 2003 study in the American Journal of Physiology, a group of men ate high-fat meals for two weeks and then low-fat meals for two weeks. At the end of each 14-day period, they each received an infusion of fat directly into their small intestines. These infusions triggered the release of CCK, so the participants should have felt full. But the men had the urge to stop eating only when the infusions followed their two-week, low-fat diet. When the infusion came after the high-fat weeks, the men actually felt hungrier than they did on the low-fat diet, though the amount of food they ate and their CCK levels were equal.

This suggests that their bodies were less sensitive to the effects of CCK when they ate fatty foods. Despite these findings, don’t shun fats altogether. Small to medium (not high) quantities of good fat in the diet not only promote health, but they help you feel satiated after a meal by releasing moderate amounts of CCK.

—Sarah Keough