I would be very careful with this diet. Although the body can withstand some fasting and there is some benefit to fasting (or, partial fasting)...it can cause your metabolism to dive, so then when you go back to normal eating, your body will need less calories due to the changed metabolism - and you could gain back the weight+++ due to this.
It can then take quite a lot to get your metabolism back up, bc the body thinks it's been in a crisis mode and is storing what it can as fat stores.
IMHO, the best diets are The Zone or Zig-Zag eating (
calculator).
Since you're seeing results though, it can then be very tough to just give up the diet. If you realllly want to use the HCG diet, then I'd recommend you do some low calorie days (at the most 2-3 days in a row) alternating w/ high calories. This is sort of like Zig Zag eating, but the HCG dives much more in low cal days. This confuses the body, and avoids plateaus (but also doesn't cause the metab to dive).
Remember, the HCG itself is likely doing very little. It's the extremely low calories that are really causing you to lose body mass (unfortunately, you'd be losing more muscle than anything else...which in turn causes the body to burn less once you return to normal eating).