The hormone helps ensure a developing baby gets enough calories in the womb. HCG tricks the body, whether male or female, into thinking it is pregnant. The hormone then forces the body to pull nutrients from stored areas of fat to feed the baby in the womb. Since there is no baby the fatty nutrients are lost.
The HCG diet is the brainchild of British endocrinologist A.T.W. Simeons. He studied two groups of people, including pregnant women in India on severely low calorie diets and obese boys with pituitary problems. Both groups were treated with HCG. Simeons discovered both groups lost fat. He reasoned that HCG could do the same for otherwise healthy people who want to lose weight.
In the HCG plan, dieters are restricted to 500 calories a day of very limited and specific foods. And the diet seems to control hunger too. Fat calories coursing through the bloodstream make people feel like they've just eaten.
One caveat, according to the plan, is that the body builds up a tolerance to HCG, so dieters must take a break every six weeks or so.
Believers say the HCG and calorie restriction together set the body up for extreme weight loss. That loss can range from one to two pounds per day, according to advertisements.
A one-month prescription for the drug typically costs about $150. Recently, the Internet has been filled with unregulated HCG products at bargain basement prices. But, many doctors caution about buying the products through the Internet because many may contain little or no actual HCG.
Several reputable medical studies, including one in the Journal of the American Medical Association, warn against the controversial diet and have called it "ineffective" and "worthless."
HCG is also not FDA approved for weight loss. Doctors must prescribe it off label for that use. Many physicians also warn that any near starvation plan can be risky. Dieters can suffer dangerous vitamin deficiencies or electrolyte imbalances, causing life threatening health problems.