The HCG (human chorionic gonadotropin) diet sets off two big red flags. First, it caps your intake at 500 calories a day when experts warn that the typical woman needs 1,600 to 2,400 calories daily, and the typical man needs 2,000 to 3,000 calories to maintain a healthy weight. (If you follow a diet containing less than 1,200 calories, you should do so only under a doctor's supervision.) Experts say such a low calorie intake can cause side effects such as gallstones, bone and muscle loss, electrolyte imbalances and heart arrhythmia. The diet isn't only calorie-restricted; you must also eat only organic meats, vegetables and fish.
Second, daily injections of HCG are supposed to curb your appetite so you can better tolerate living each day on what one source calls "the energy equivalent of a turkey sandwich." HCG is approved by the FDA for use only by prescription and to treat very limited conditions, mainly fertility; HCG is not approved for over-the-counter sale, or for treating overweight or obesity.
The HCG injections come with additional risks such as decreased sperm production, male breast enlargement, headaches, long-term breast cancer risk, fatigue and blood clots. One expert calls the diet "utter and dangerous nonsense," and warns that it can even kill you. Another says this sort of extreme calorie restriction isn't sustainable, and doesn't create the kind of lifestyle change that prevents dieters from regaining the weight.