Ever wondered why you tend to overeat when you are stressed? Well, a study has the answer finally -- it's due to "hunger hormone" ghrelin which also has an "anti-depressant" effect.

It is known that fasting causes ghrelin to be produced in the gastrointestinal tract, and that the hormone then plays a role in sending hunger signals to the brain.

Now, a team at the University of Texas has found that ghrelin increases during chronic stress which in turn triggers feelings of hunger in the brain -- however, behaviours linked to anxiety decrease when the "hunger hormone" levels rise.

According to lead researcher Jeffrey Zigman, "Our findings suggest that chronic stress causes ghrelin levels to go up and behaviours associated with depression and anxiety

decrease when ghrelin levels rise. An unfortunate side effect is increased food intake and body weight."

The researchers have based their findings on an analysis of rodents -- they restricted the food intake of the mice for ten days, thereby causing the ghrelin levels of the animals to quadruple.

Compared with rodents who had free access to food, their calorie-restricted counterparts showed lower levels of anxiety when being subjected to mazes and other behaviour tests, the Nature Neuroscience  journal reported.

The team also looked at mice genetically engineered to be unable to respond to ghrelin. When they're fed a restricted calorie diet, they did not experience the antidepressant or anti-anxiety effects.

The researchers found the same thing when they induced higher ghrelin levels by subjecting the mice to stress. Those who couldn't respond to ghrelin had higher depression levels like symptoms than the normal mice.

"Our findings support the idea that these hunger hormones don't do just one thing; rather, they coordinate an entire behavioural response to stress and probably affect mood, stress and energy levels," the ScienceDaily quoted the study's lead author Dr Michael Lutte as saying.