Many processed carbs have very little natural vitamins or oils left once they have been processed so they are mostly useless calories, and many have very high glycemic indexes, meaning they tend to spike blood sugar levels, which signals your body to store fat. Even though they may say whole wheat on the label, you never know for sure what elese they might put in prepared foods: transfats, lots of salt, high fructose corn syrup or other sugars, "enriched" flour, etc. You just can't beat good old fruits and vegetables as the best source of carbs with most of the natural vitamins and other trace nutrients still intact.