[See: Best Diets for Healthy Eating.]
Detractors say the hormone isn't some miracle ingredient to weight loss—the restrictive diet is. "If you don't eat, you lose weight," Cohen says. "If hCG truly diminished hunger, it would be a wonderful drug. But if that were the case, why couldn't you just modestly reduce your intake while using it? Why would you have to simultaneously starve yourself?" But believers insist that, thanks to hCG, they can stick to a low-calorie diet without hunger pangs, while losing unwanted fat. They're adamant that hCG is essential to the diet's success. "People are strongly convinced that this hormone will keep them on a 500-calorie diet. And the power of suggestion can be a very strong force," says Cohen.
Of course, the regimen isn't without risks. The hormone is known to cause headaches, blood clots, leg cramps, temporary hair thinning, constipation, and breast tenderness. The FDA has received at least one recent report of an HCG dieter developing a pulmonary embolism, a potentially fatal blood clot in the lung, says agency spokesperson Shelly Burgess. Yet, the hormone's full risk profile is unknown. "HCG was studied briefly [for weight loss] and found to be ineffective, so we have no idea what its potential risks are," Cohen says. "Do I have data that it causes heart attacks, stroke, or cancer? No, I don't, because we just don't know at this point." While hCG may be safe on its own—the FDA says it's safe as an infertility treatment—pairing it with an extremely low-calorie diet could have unexpected side effects.
Two years ago, Lori Hill, 40, of Salt Lake City, Utah, began a 28-day hCG diet cycle. She says she lost about 26 pounds, including thigh fat, largely without hunger. But she felt ill almost immediately, and by the last week of the diet, Hill—a fit and active soccer referee—couldn't climb a flight of stairs without gasping for breath. The effort made her muscles burn and shake, too. After completing the cycle, Hill regained all the weight she had lost, plus an additional 15 pounds. "I starved myself and threw all my nutrients out of whack," she says. "You're tricking your body into letting you starve, without feeling any major hunger. What you're doing to your body just isn't worth it."
[See: Unusual Uses for Greek Yogurt.]
There's no question that 500 calories a day is tantamount to malnutrition—dieters should never dip below 1,200, say experts—and federal dietary guidelines recommend more than three times the amount of calories the diet prescribes for women ages 19 to 30. Moreover, extremely low-calorie diets can cause severe bone and muscle loss, electrolyte imbalances, gallstones, and even death. "I've heard a lot of people say the side effects of this diet are overwhelming," says registered dietitian Keri Gans, a spokesperson for the American Dietetic Association. "And they could start as soon as one day in—you'll start feeling irritated and tired."
To Gans, the regimen is nothing more than a crash diet—and an expensive one at that. A more sensible route to weight loss, she says, is no more mysterious than choosing healthy foods, limiting portion sizes, and exercising. "This is another approach for people who believe there's a silver bullet, but there is no such thing. All this diet does is show you how to restrict, and a person can only do that for so long without returning to old habits."
[See: Unusual Uses for Avocados.]
Angela Haupt is a health reporter for U.S. News & World Report. You can follow her on Twitter or reach her at firstname.lastname@example.org.