Scientists have identified another hormone involved in regulating hunger.
The hormone helps in controlling appetite
Obestatin joins a raft of other hormones which can boost or suppress a person's appetite.
The team at Stanford University, US, carried out a computer search of genetic information which led to obestatin, Science magazine reports.
A UK expert said that the research would help enable scientists to fully control appetite within the next five to 10 years.
The researchers looked at gene sequences in humans and animals, including one which codes for ghrelin, an appetite-boosting hormone.
They found another hormone - later dubbed obestatin - was processed from the same protein precursor that produced ghrelin.
But obestatin was found to suppress appetite - the opposite effect to ghrelin.
When rats were given injections of obestatin in their abdomens and brains, they ate about half as much as animals who were not given the hormone.
They also put on less weight.
Obestatin also slowed the movement of food from the stomach to the intestines.
Writing in Science, the researchers led by Dr Aaron Hsueh said: "A better understanding of the roles of ghrelin and obestatin in the intricate balance of energy homeostasis [equilibrium] and body weight control may be essential for the successful treatment of obesity."
Professor Steve Bloom, an expert in obesity research at Imperial College, London, said: "This is a fascinating piece of research.
"It points to another part of the complex appetite-regulating system that we could affect using a drug."
Professor Bloom said it added to other discoveries about how hunger is regulated, and added: "We should be able to control appetite within five to 10 years."
But the fact that an appetite suppressing hormone is made by the same cell as an appetite boosting one was "a bit of a puzzle".