HCG is a naturally occurring hormone in the body known as Human Chorionic Gonadoprtopin. HCG is produced by both men and women naturally and it has many functions within the body. The most relevant is the ability to send signals to the Hypothalamus. The Hypothalamus is the part of your brain that controls your thirst, temperature, fatigue, metabolism and hunger. Since HCG has the ability to communicate with this part of the brain it becomes a fat burning mechanism.