Instead of completely eliminating things from your diet, try just modifying your diet a little bit.
I love mashed potatoes too, and the potatoes themselves are not as horrible as everyone believes. However filling them with butter, cream cheese, salt, and/or sour cream can double the calories that t hey contain.
I suggest removing some of the condiments you add on to your food to begin with. Stop putting salt on your food, reduce the butter or sour cream you put on your potatoes. Switch to a multi-grain pasta rather than just the normal. Some of these changes may seem minor but they can add up and you'll probably see a good result because of it!