If you stick to your plan of observing portion size and such you'll be fine. I finished R3 in September, went through P3 and maintained my weight just fine. Even through a few rounds of steroids for an autoimmune flare I only gained 12 pounds - which I've now lost. If you go back to eating high processed foods everyday then most likely you will see a gain. For me it's a give and take thing...if I know I'm going to be "bad" one day then I know I have to be "good" a couple days too. Balance.