Call it what you will: the battle of the bulge, middle-age spread, the waistline war. Somewhere in that busy time between 30 and 40, the forces of nature—children, work, time—gang up on you. One day you notice last season's clothes are a little uncomfortable this time around. All this comes at a time when age is less acceptable as an excuse for gaining weight. Just look at the current U.S. Dietary Guidelines, which make no allowance for getting heavier through the years. Getting older doesn't have to mean getting wider, the experts say. The first step in the fight against flab is knowing your opponent. Take the following quiz to find out how well armed you are.