Human Chorionic Gonadotropin--commonly referred to as hCG--is a naturally occurring hormone. The body produces hCG during pregnancy to metabolize fat as an energy source for the growth and nourishment of the baby. hCG works with the hypothalamus gland, a part of the brain that regulates appetite, digestion, metabolism and fluid levels. What makes hCG different from dieting alone is that many restrictive diets trigger a "starvation mode," putting the brakes on your metabolism and actually causing fat storage. Oral or injected hCG combined with a reduced calorie meal plan (500 calories per day) stimulates the body to mobilize stored fat, making it available to your body as an energy source. This means fat is burned instead of muscle, without the typical hunger pangs one would experience with a low calorie program.