Poke that spare tire around your waist (if you have one, that is. If you don't, kudos to you!). It might not look so good, but it seems innocent enough, right? Guess what? It's not. Just ask researchers, who are learning that fat is anything but inert. It actually plays a powerful role in a body's health, they say.

Everyone has fat cells; babies are born with up to 10 billion of them. As we gain weight, fat cells expand and new cells are created. An obese person may have up to 100 billion and even when weight is lost, the number of fat cells does not decrease. But beyond their sheer number, fat cells act negatively on the body. While normal-sized fat cells release hormones that help the body, over-sized fat cells have the opposite effect, releasing hormones that increase inflammation and preventing good hormones like those that reduce the body's resistance to insulin.

So while you might be motivated to lose that spare tire for that tropical vacation you have planned this winter, there's a much bigger, more important reason to lose it -- your good health.