Atkins Pounds Other Popular Diets in U.S. Test

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Replacing carbs with fat and protein may have helped, too. "Remember, you can eat a lot of rice or pasta before you actually feel full," said dietitian Tara Miller, program director of New York University's Center for Corporate Wellness. "With a high-fat diet, you are going to fill up faster."

Still, a one-year trial, however well-conducted, is simply not long enough to gauge the long-term safety of any "extreme" diet, the experts said.

Because blood glucose reacts particularly strongly to excessive carbohydrate intake, lowering carbs "might assist blood sugar control," said Harvard endocrinologist Dr. Barbara Kahn. "But the [potentially] harmful part has to do whether all those fats over the years are going to lead to more cardiovascular disease. That's the next thing that needs to be studied."

Whether most people can even stick to the Atkins, Zone or other plan for a year or more may be the real question, Miller said. "None of these diets are things that you can maintain day to day without a lot of forethought," she said. "If it does not fit your lifestyle, no matter how great a diet it is, it is not going to benefit you, because you aren't going to be able to maintain it."

That's a lesson Richard Boucher, a 42-year-old construction equipment salesman from Placentia, Calif., learned the hard way. Boucher -- who has been battling his weight since his early 30s -- first turned to the Ornish, Zone and South Beach diets for help. He'd drop some weight, but the diets' tough restrictions beat him every time, he said.

Since then, Boucher has brought his weight under control, slimming down from a top weight of 270 pounds to the 200 pounds he maintains today.

But first, he had to throw out all his diet books.

"I found that a common-sense approach works best for me," Boucher said. "A lot of portion control -- when I'm full, I just walk away. I stay away from lots of pasta and sugars. I exercise regularly. In the end, you have to do what makes sense and works for you."

More information

Find out more about healthy weight control at the American Dietetic Association.