The body weight simulator, originally a web based java application, is now also an iPhone app (see here in iTunes). The simulator is based on the human metabolism model developed by Kevin Hall, myself, and collaborators. The exact model is given in detail in our Lancet paper, which is listed here along with other related references. The app predicts the time course of your body weight given your baseline parameters and your new diet and/or new physical activity. It will also give a suggested daily caloric intake to attain a new weight over a specified period of time along with the diet required to maintain that weight. The model uses parameters calibrated to the average American so your own mileage will vary. Also, I basically wrote the app in my spare time over the past year so it is pretty primitive as far as apps go but it does the job. Please try it out and give me feedback.