your body isn't a simple formula. It won't always follow that by eating as little as you can that you'll be maximising weightloss.
Human bodies aren't designed to be overweight, they are designed to survive on what they are given on a day to day basis. If you shrink your input, it shrinks the metabolism in response...
So not only will you not lose weight, you'll eventually start to suffer when you no longer enjoy starving yourself...go on a big binge and put all of the weight back on... either that or your body starts consuming its muscles and eventually gets to the heart (the reason why anoerexics die)