You can actually lose weight on 2000 calories a day, especially if your calories are just protein and fat – but your weight will creep off so slowly, the big bet is you won’t stay consistlently enougn on 2000 calories to lose weight in the long run. I’m a big fan of starvation weight loss programs, that provide enough protein to spare your lean body mass. This is because weight loss has to be rapid and dramatic, in order for you to put up with the deprivation of caloric restriction. 3000 calories a day is a lot more fun than 1000 calories a day. And the magic number for losing weight is generally no more than 1500 calories of protein and fat a day. Once a day I see a patient who hasn’t cheated a bit on a very low carbohydrate diet all week, but they’ve only lose a pound or two. The problem is their calories are in stupidville. If you want to lose weight fast enough to stay on your diet, you’ve got to starve yourself. There’s no other way.