I also understand very much how Anorexics and Bulemics get very involved in their weight to the exclusion of all else.
Simply put, your body gets used to being a certain weight. As long as it's at that weight (or slightly above), you're satisfied with the world at large. Run a bit below that (say, five pounds) and your body starts yelling for food. Your mind focuses on food and on resisting the urge to eat, slowly pushing aside all other thoughts.
My guess is that, push the weight 30-50 pounds below where you're at and food becomes the sole focus of your thoughts. The body so much wants to get back to its pre-diet weight, and resisting the urge takes up so much effort that other things become
I've been taking Hoodia off and on during the past month. It does work in that it takes the edge off the hunger, so you don't feel as pushed to eat as before. However, the rest of the body starts yelling for its food, once you take your weight below a certain level. There's also some side effect (throat seems a bit swollen, though not enough to choke you), and it is possible to overcome the hoodia (one sunday I swallowed a pill, then proceeded to eat a big dinner and a double-dip ice cream cone).