Fat can play a major role in chemically curbing the appetite, according to research by a team of UC Davis nutritionists. The researchers found that when laboratory rats were fed meals containing the same amount of calories, but with varying levels of fat content, those receiving more fat ate less frequently and consumed fewer daily calories. The study suggests that two substances -- CCK (cholecystokinin), a hormone produced in the small intestine, and serotonin, a chemical found in the brain and intestines -- are involved in the satiating effects of fat. "This is a controversial topic, because some scientists maintain that protein and carbohydrates are more potent than fat in producing satiety," says Britt Burton-Freeman, a doctoral candidate, who conducted the study in the UC Davis nutrition department. "Our research, however, clearly indicates that fat triggers a hormonal release that signals the brain that the body is satiated," she says. She presented the findings this month at the annual meeting of the Federation of American Societies for Experimental Biology.