Eating Habits Not Sole Cause of Thinness or Obesity (HealthDay)

WEDNESDAY, June 4 (HealthDay News) -- Your nerves, rather thanyour eating habits, may have a more direct role in whether you are fat orthin, according to new research.

A study on worms shows that serotonin levels in the nervous systeminfluence feeding and fat. Serotonin, a neurotransmitter, also actsindependently to control eating and what your body does with thosecalories once they've been consumed, the study said.

"It says that the nervous system is a key regulator coordinating allenergy-related processes through distinct molecular pathways," KavehAshrafi, of the University of California, San Francisco, said in aprepared statement. "The nervous system makes a decision about its stateleading to effects on behavior, reproduction, growth and metabolism. Theseoutputs are related, but they are not consequences of each other. It's notthat feeding isn't important, but the neural control of fat is distinctfrom feeding."

Ashrafi said that given serotonin's ancient evolutionary origins, youcan apply what's learned from the worms to humans.

"From a clinical perspective, this may mean you could developtherapeutic strategies to manipulate fat metabolism independently of whatyou eat," he said. "Now, the focus is primarily on feeding behavior. Asimportant as that is, it's only part of the story. If the logic of thesystem is conserved across species, a strategy that focuses solely onbehavior can only go so far. It may be one reason diets fail."

The findings were published in the June issue of CellMetabolism.

At its most basic level, fat regulation is the balance between energyintake and expenditure; however, Ashrafi said the physiology is verycomplicated.

In the worms, serotonin affected feeding by involving nerve receptorsnot normally required for fat control. The byproducts of the signalingprocess ended up affecting the control of feeding behavior, Ashrafisaid.

In the worms and in mammals, high serotonin levels are associated withfat reduction, while low serotonin levels lead to fat accumulation, theresearchers noted. However, in the worms, when serotonin goes up, theworms desire to eat increases even as fat melts away. But in humans, highserotonin leads people to eat less and shed fat.

Serotonin's effects on fat and eating habits in the worms fit thenerve messenger's role as a sensory gauge of nutrient availability, theresearchers said. When resources are scarce, worms build up their fatreserves and switch metabolic gears to save energy and direct nutrients tofat stores.

Ashrafi said serotonin's role in balancing energy across species leadshim to believe that "human counterparts of feeding-independent fatregulatory genes identified in our study may similarly regulate energybalance."

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