Potatoes are not bad, especially if you want to gain mass they can be helpful, just eat them early in the day and you should be fine. Brown rice is not bad either. Eating white rice or white flour though and you might as well just eat big spoonfuls of sugar.
Juice blows because of the massive carb load it carries.
BTW ty, I got a new song coming out soon, it's a rocker... it is the theme song for The Summer of Ripped Abs, and it will be performed live. At the end of the track, I will rip off my shirt a la Hulk Hogan, and a spot will shine on my glistening oiled up ripped abs, while a fan blows on me.
-jlaix