A sick or sad child might cling to mom's leg. But that same child - fed, rested and generally content - will happily toddle off to explore every nook and cranny of the known world. Or: You're chipper and you decide to check out the new restaurant across town. You're blue and you turn to comfort foods...

A sick or sad child might cling to mom's leg. But that same child - fed, rested and generally content - will happily toddle off to explore every nook and cranny of the known world. Or: You're chipper and you decide to check out the new restaurant across town. You're blue and you turn to comfort foods...