I personally think the question itself is flawed.
What causes weight loss is ingesting less calories than you use. Beyond that what matters is having a plan you can stick to. For some this might mean restricting carbs. For others it might mean tracking calories. The question is flawed because any diet that restricts calories works. There is no magic fairy dust at work. Stop thinking diet and start thinking lifestyle.
/RANT
HCG diet works because you're massively restricting calories. Wether you have fake drops that do nothing or you are being injected by a doctor with actual HCG that does almost nothing the reason you're losing weight is calories. Anyone who is thinking about doing HCG should
read this. After you've lost the weight what then? You haven't learned sustainable life habits.