Man, I understand this! Last night I also was in one of those, "Well, a few crackers wouldn't hurt me..." moods, when a commercial came on full of skinny girls in bikinis. I got a glass of water instead.
So apparently that's all it takes-- reinforcement. Put some pictures on your fridge and cupboards of overweight and healthy people, so the difference will be blatantly obvious. Every time you want to go for food, you'll see them and have to make a choice.