People will go to great lengths to lose weight quickly, no matter how painful or madcap the plan. Here's the proof: The HCG diet involves daily injections or supplements of human chorionic gonadotropin (hCG) -- a pregnancy hormone that's been approved as an infertility treatment, but shows little evidence that it helps people lose weight [source: Nelson]. The hormone coupled with intense calorie restriction is at the heart of this diet. Sadly, severe calorie restriction can have deleterious health effects, including the inability to fulfill one's nutritional needs. Also, hCG's side effects may involve headaches, fatigue, irritability and male breast enlargement.