Go to the grocery store hungry and you're bound to crave everything in sight. Blame your "Mmm" hormone, says new research that names the natural molecule ghrelin the responsible party.

Why ghrelin? Because it improves perception and memory when it comes to food. When hunger strikes, watch out, because ghrelin makes the brain find just about every food appealing, sending us on a path to diet destruction.

Researchers have long known that ghrelin, a hormone secreted in the gut, rises and falls before and after meals. Now they're learning that this "Mmm" hormone has even more power -- it causes hunger and encourages eating.

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