Actually I weigh around 150lbs and I'm 5ft6. I've not been sedentary - I've been doing martial arts for just under 3 years now. However, I'm focussing on cleaning up my (shitty) diet, one step at a time.
Right now, I've cut out sugar, caffeine and white flour. I'm going NUTS argh. Day 3 of withdrawal today.... By Saturday the cravings should be gone. This is why I'm eating quite a bit of fruit - once I get over the sweet cravings I will be replacing the fruit meal-by-meal with green veggies. No binges so far, I'm pleased.
Here in Scotland they not only make every conceivable type of oatmeal, they make oatmeal biscuits, (oatmeal, water and some raising agent I think) mmmm. 50 cals each, lotsa fibre, low GI. 4 of these with hummus make a nice lunch....