I kinda picked up that obsession too. I struggled to get past it, and to some degree I still am. Here's the problem:
You can't eat next to nothing forever. I'm sure, theoretically you could but It would certainly shorten your lifespan. Sure you might get thinner - weigh less and all that good stuff but your body can only handle that kind of abuse for so long. Jen's absolutely right about losing the fat and keeping the muscle mass. Alot of lean muscle mass takes more caloires to maintain than the same ammout (by weight) of fat.
Start off by figuring out how much you need just to maintain the weight you're at right now. Search for "BMR calculators" online and that will give you a pretty good idea of how many calories you burn daily (just existing - not including any activity). Finding that helped me relax a little knowing that I could get a bare minimum of 1500 cals a day without gaining.
I had to learn to shift from one obsession to another in order to get past it. So I began to focus on figuring out how I could get all the nutrients and fiber I need every day without driving myself (or my family) nuts. I also began to catalog all the foods I felt like I was missing out on (there were alot more foods I missed than I realized). My next step was to attemp to convert those beloved goodies into something more healthy. What I now have is a recipe book with converted recipes for all sorts of "no-no" foods - like fettuccini alfredo, oatmeal raisin cookies, creamy cheesy chicken and rice, and butternut squash pie (sounds scary - but really really tasty).
To make a long story longer
If you MUST obsess over anything (and I must, it's just how I am), obsess over something that will be worthwhile in the long run. It's not just about the scales. Everything is connected to the way you eat. You skin, nails, hair, energy levels, and emotional well being suffer when you don't get enough of what you need. You also gain it back faster if you never learn to eat healthy.
start: 310 (Oct '04)
goal: 150 (Feb '06)
current: 135 - and holding
Total loss: 175 via WW, excercise, and loads of support.