You can hardly loose any weight if you are not on low calorie diet, with or without HCG. It is easy to get rid of first few pounds because at beginning we all loose liquids, when it comes to the loosing of fat deposits - real problems start, because every 2 pounds of fat deposits is equal to aprox. 9000 calories. So it is not easy to burn it.
500 calories diet can be OK for some people, but many need more, like 700-1000) even with HCG. But low calorie diet is always needed.
But more important then counting calories is type of food you eat - some food make us overweight no matter how many calories it has. If your body does not attain healthy dietary habits while on HCG and diet, when you stop using HCG, your fat deposits will come back.