Oleic acid triggers a reaction in the body that staves off hunger pangs and tells the brain, "I feel full."
Scientists believe the same signalling pathway could be targeted by drugs to control appetite and treat obesity.
A reverse approach could improve appetite in people do not eat enough, such as anorexics.
Only unsaturated fats containing oleic acid regulate food consumption in this way, the research found.
Saturated fats which are abundant in processed foods and lack oleic acid upset the system and encourage more eating.
Dr. Danielle Piomelli, one of the scientists from the University of California at Irvine, said, "Eating is one of the most important things animals do.
"This is just one of many things that control it. That said, a system like this could be forced to inactivation by inappropriate feeding."
Work on rats showed that when oleic acid reaches the small intestine, it is converted into a fatty lipid hormone called oleoylethanolamide (OEA).
OEA in turn stimulates nerves that send messages to the brain warding off the next round of hunger pangs.
Piomelli previously demonstrated that OEA not only curbs appetite but reduces weight and lowers levels of cholesterol and harmful triglyceride in the blood.
The new research showed for the first time that an ingredient in unsaturated fats such as olive oil stimulates OEA production.
Protein and carbohydrates did not have the same effect.
Drugs that mimic the action of OEA or prevent it being lost could help control the appetites of people who are overweight or obese, the researchers believe.
Writing in the journal Cell Metabolism, they concluded, "Our studies identify OEA as a key physiological signal that specifically links dietary fat ingestion to across-meal satiety.
"Nutritional and pharmacological strategies aimed at magnifying this lipid-sensing mechanism, such as inhibitors of OEA degradation, might be useful in the treatment of obesity and other eating disorders."
From the October 13, 2008, Prepared Foods e-Flash