When I started to fix my diet I had to purge myself of Caffeinated sodas first. I found the combination of HFCS and caffeine would make me crave junk food like an addict. I purged myself of the caffeine and ate junk food then after a few weeks purged the junk food and now I can turn away from the bag of potato chips without too much willpower.
Having gotten off of physically addictive drugs before I recognized the feelings and realized how much I had to slowly ween myself off of that stuff.