Hunger can make you happy — or at least motivated:
When our bodies notice we need more calories, levels of a hormone called ghrelin increase. Ghrelin is known to spur hunger, but new research suggests this may be a side effect of its primary job as a stress-buster.Researchers manipulated ghrelin levels in mice through a variety of methods, including prolonged calorie restriction, ghrelin injection and a genetic modification rendering the mice numb to ghrelin’s effect.
Mice who had limited ghrelin activity seemed depressed. If pushed into deep water they made no effort to swim. When introduced to a maze, they clung to the entryway. And when placed with other mice, they tended to keep to themselves. (These behaviors were reversed when the mice were given a low-dose antidepressant commonly prescribed to humans.)
In contrast, mice with high levels of ghrelin swam energetically in deep water, looking for escape. They eagerly explored new environments. And they were much more social.