The U.S. Food and Drug Administration calls hCG supplements illegal and fraudulent, and prevents direct-to-consumer sale. But because hCG is approved for other reasons, such as fertility treatments, doctors can prescribe it if they choose.
Stories of hCG diet success are easy to find; no surprise given the dramatic caloric restriction involved. But while the initial results may be motivating, the diet is not very sustainable.
"You might lose weight fast but you'll gain it all back when you go back to living like a normal person, again," Katz said. "And if you do stick with it, you'll be very thin but I doubt you'll be very healthy."
Weight-loss programs that combine more modest calorie reduction and exercise are a better bet for keeping the pounds off, Katz said.
"The hCG diet is not only a silly fad diet," he said, "but it's also a dangerous one."