It's not fat or carbs, SUGAR is the key. When people ask me what is one thing they could do to make an impact in their nutrition, I say to eliminate processed sugar.
There is a whole host of reasons for this but a couple are how it raises your blood sugar which raises insulin, which isn't good health wise and inhibits bodyfat usage. Another is that sugar digests quickly and often causes one to want more.
Pass on the junk, bring in the good! I'm a fan of sugar free gum and Walden Farms syrup flavors, anyone else have a sugar substitute they like?