Why the 500 calorie diet (VLCD very low calorie diet)?

You are on a VLCD (very low calorie diet) of 500 calories because while you are on the HCG, your body is releasing 1500-4000 calories from abnormal fat into your bloodstream each day. So, with the 500 calories you are consuming plus the 1500-4000 calories being released into your system, you are actually getting the benefit of (500 + 1500-4000) = 2000-4500 calories each day.