Unless you have insulin resistance, that is. Insulin, for all those who don't know, is the hormone that allows cells to take in sugar to metabolise. It is produced by the pancreas, and when ever you take in sugar, it send some into the blood stream. Some of you may remember that this is related to why you are hungry shortly after eating something sugary: your body sees a lot of sugar coming, so it dumps insulin, but sometimes it dumps too much, so it needs sugar to compensate, which make you hungry. What isn't so known about is insulin resistance. They are not sure what exactly causes it (some things seems to suggest it is genetic to a certain extent), but what happens is that the normal insulin isn't enough for most cells. It is a lot like how you develop resistance to a drug: your cells need more of a fix to do the trick, so to speak. This has a few consequences, including:
A. It can cause you pancreas to work over time, which can lead to type two diabetes.
B. Apparently, fat cells don't need as much insulin to take in sugar, so guess where all the extra sugar goes. Thats right, straight to your hips.
So yes, sugar can make you fat, even if you do exercise a lot. There are two ways to get around insulin resistance. One, obviously, is to consume in moderation. Two, is to eat foods that release the sugar more slowly, so your body has time to deal with it. Some foods, like cookies, crackers, and white bread, start becoming glucose almost as soon as they enter your mouth. Other foods, such as wheat breads, brown rice, and oatmeal, release it more slowly, because the fiber gets in the way some so that sugar can't rush to the blood stream.
On a slightly side note, oatmeal is some amazing stuff. It can actually lower the blood sugar of a diabetic, and is know for all kinds of healthy benefits. Now we know where "healthy as a horse" came from.