Why is it so hard to walk by a bakery and resist all those sweet treats inside just calling your name?

It turns out donuts have given scientists an important clue to why it's so hard to control our cravings.

Researchers took brain scans while people were looking at pictures of donuts. Once after they hadn't eaten for eight hours. And again after they had just gorged themselves on eight donuts.

Perhaps not surprisingly, their brains didn't show much of a response after they had just devoured the donuts. But the scans showed that after their fast a part of the brain called the limbic system lit up when they saw the donut images.

The researchers say this response is the brain's way of focusing its attention on what it needs most in this case, food.

So the next time you're going to be passing a donut shop and want to resist temptation make sure your stomach is full, hopefully with something a little less decadent.