Although the hCG diet is slightly outside of the realm of The Pregnancy Lab, we have discussed it in the past because we get questions about it all the time. Don't even consider doing this diet to shed your extra holiday pounds. On December 6, 2011, the FDA and Federal Trade Commission issued warnings to a number of companies ordering them to stop selling their homeopathic hCG products. The warning letter states that, it is unlawful to "advertise that a product can prevent, treat, or cure human disease unless you possess competent and reliable scientific evidence". In addition, the FDA says a 500-calorie diet by itself is pretty risky. You can get gallstones and develop other health problems from such severe restrictions on what you eat.
If you are considering this or any diet a good resource is an article by American Dietetic Association.