University of California, San Francisco, researchers said extensive studies have revealed that body weight is not merely a passive consequence of environmental conditions -- diet and exercise -- but that a physiological system coordinates the complex mechanisms that regulate food intake and energy expenditure.

Study author Kaveh Ashrafi said that increased eating does not necessarily lead to increased fat.

The study, published in the journal Cell Metabolism, said the neurotransmitter serotonin -- already known to control appetite and fat build-up -- actually does so through two separate signaling channels. One set regulates feeding, and a separate set regulates fat metabolism.

"If the 'separate-channel' mechanism is also found in humans, weight-loss drugs might be developed to attack just the fat-deposition channel rather than the hunger-dampening pathway that has met with limited success," Ashrafi said in a statement. "It's not that feeding isn't important, but serotonin's control of fat is distinct from feeding. A weight-loss strategy that focuses only on eating can only go so far. It may be one reason why diets fail."