I might be wrong but isn't pasta just as bad for putting on weight as chips (obviously I mean oven cooked chips not macdonalds chips or fried chips dripping with fat).
Maybe you could join a gym, some of the machines they have there work well for building up/toning muscles which is better for calorie burning as it continues to burn more calories throughout the day.
But I also think generalebriety is right, you definatly shouldn't be aiming for the seven stone mark, it's too little, at the most all you should be doing is shedding a few pounds/toning up.