HCG stands for human chorionic gonadotropin. It's a hormone produced by pregnant women. The HCG diet is a diet created by a british endocrinologist named Albert Simeons. Through experimentation he came to believe that low doses of HCG would cause the body to loose irregular fat during periods of low calorie eat. The diet consists of taking a shot of HCG once a day and eating 500 calories from a very strict food regimen. 100g of meet, 1 vegetable, 1 fruit and for some one bread stick (which I am not eating). The idea is to keep the calories to 500 a day for either 20 or (in my case) 40 days. People on this diet typically loose 20 to 40 pounds of the worst body fat while on the first part of the diet. There are three or four parts to the diet depending on who you ask. There is a gorging phase, followed by the vlcd, followed by a carb restricted period of eating and then controlled "normal" eating. The HCG helps suppress the appetite and the over effect if the diet is to induce ketosis. Because the diet induces ketosis, your body is burning irregular fat for a fuel source, there is little or no hunger and you don't loose muscle despite the low calorie eating. It is also believed that because of the low calorie eating people on the diet learn new habits towards portioning and portion control. Some people claim that the diet resets the endocrine system, retrains the hypothalamus and reconditions people for better eating practices. This diet is also often recommended for people with thyroid problems and people with other conditions that lower their metabolism.