Clash of the Weight Loss Titans

March 6, 2007 -- Which popular diet plan helps you lose the most weight: the Atkins Diet, Barry Sears' Zone Diet, the Ornish Diet, or the LEARN program?

To answer that question, Stanford University researcher Christopher D. Gardner, PhD, and colleagues randomly assigned 311 overweight and obese women to one of the diets. The idea was to see what worked best for weight loss: a very low-carb diet (Atkins), a low-carb diet (Zone), a low-fat, high-carb diet (LEARN, based on U.S. guidelines), or a very high-carb diet (Ornish).

Gardner's team made sure the women understood the diets by having an enthusiastic nutritionist teach them their assigned program in eight weekly sessions. Then they pretty much left them to follow the diet books for the rest of the yearlong study.

What happened?

At the beginning of the study, the women's average weight was 187 pounds. All of them, Gardner says, needed to lose at least 15 pounds -- and many needed to lose 40 to 80 pounds.

After a year, some of the women in each group lost as much as 30 pounds. Twice as many lost this much in the Atkins Diet group as in any other group. Overall, here's how much the women lost on the four diets:

• Atkins Diet -- 10.4 pounds on average
• LEARN --  5.7 pound average
• Ornish Diet -- 4.85 pound average
• Zone Diet -- 3.5 pound average

The weight loss difference between women assigned to the Atkins Diet and women assigned to the Zone Diet were statistically significant. The other differences were not – meaning they could be chance findings.

Gardner and colleagues report the findings in the March 7 issue of The Journal of the American Medical Association.

Did the Atkins Diet Win? Some Say Yes

What do the results mean? That depends on who you ask.

Gardner says the study highlights how difficult it is for people to follow the Zone and Ornish diets on their own.

He points to two American dietary trends: We are eating more and more calories. And we are eating more and more refined carbohydrates in the form of sweets, sodas, and snacks.

He suggests that the Atkins Diet offers a simple way of counteracting these trends.

"Dr. Atkins just said, 'Don't eat any refined carbs, period.' And the carbs you do eat must be good, healthy carbs," Gardner tells WebMD. "And that is very much tied to the trend that is going on in the U.S. obesity epidemic. Maybe that is why the Atkins Diet was a little more effective."

Jeff S. Volek, PhD, RD, assistant professor of kinesiology at the University of Connecticut, has studied the Atkins diet in research partially funded by the Atkins Foundation. Volek says Gardner's findings extend and confirm previous research.

"Those assigned to the Atkins Diet had lower carbohydrate intake than the other three groups. So it is valid to conclude that the differences are due to carbohydrate intake," Volek tells WebMD. "We have been trying to say it is the carbs that are driving the physiology of weight loss and that we should be talking more about carb restriction than about fat restriction."

But this interpretation isn't unanimous.