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.
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.
Did the Atkins Diet Win? Some Say No
"What this study showed, yet again, is how difficult it is for people to lose weight no matter what the approach," Yale University psychology professor Kelly D. Brownell, PhD, tells WebMD.
Brownell wrote the manual for the LEARN weight loss program. Nutrition is only one part of the program, which also aims to help people change interpersonal relationships, improve physical activity, change behaviors, and change attitudes.
"The people trying to follow the Atkins diet lost about 10 pounds and the others lost about five pounds. Nobody will be terribly excited about those five extra pounds, given that where they started out was at 187 pounds," he says. "The message isn't that Atkins is better; it is that nothing works very well for people who are already obese."
Zone Diet creator Barry Sears, PhD, notes that none of the groups in the Gardner study followed their assigned diet plans.
"These results have no meaning in either the real world or in the world of controlled studies," Sears tells WebMD. "This is one of the first times Dean [Ornish] and I are going to agree. Even if Bob Atkins were here, he would say, 'This is not my diet.' You have the three tenors singing together, 'This is not my diet.'"
Those assigned to the Atkins Diet, he says, actually ate foods much more like those recommended in the Zone Diet.
"These patients were getting three times the amount of carbs recommended by the Atkins Diet," Sears says. "By the end of the study, they were eating 140 grams of carbohydrate a day. Bob [Atkins] never recommended more than 50 grams a day. I recommend 100-110 grams of carbs a day. So essentially the Atkins Diet was the Zone Diet in this study."
As Sears predicted, Dean Ornish, MD, agrees that the "Ornish Diet" that Gardner's study participants followed is not the Ornish Diet he created.
"What is frustrating to me is they were not following a diet I recommend," Ornish tells WebMD. "Dr. Gardner did not test what these diets do; he only tested how easy they are to follow. It is easier to eat bacon and brie than to eat healthy foods. But that doesn't mean it is good for you."
Healthy Weight Loss
Gardner and colleagues didn't just weigh the women trying to follow the four very different diet plans. They also did blood studies to look for heart diseaserisk factors.
"All four groups benefited for blood pressure and cholesterol levels and insulin sensitivity -- all the things you would expect from weight loss," Gardner says. "It is nice to know you get those things with modest weight loss. You don't have to lose 100 pounds. If you lose 5% to 10% of your body weight, you get a benefit."
Ornish says it's just plain wrong to assume from the Gardner study that the diet plans are equally healthy.
"To say the Atkins Diet is no more harmful than the Ornish Diet is dangerously misleading," he says. “Dr. Gardner and colleagues say the heart-disease risk factors were comparable on all four diets and then they said that Atkins doesn't harm you. But risk factors are just risk factors. In our studies, we actually measured heart disease itself, not just risk factors. And we found that on the Ornish diet, people with heart disease showed clear reversal after a month, more after a year, and even more after five years.”
Volek has a very different view.
"Reducing carbohydrate intake is a very effective option for losing weight, improving health, and reducing the symptoms of the metabolic syndrome -- high blood pressure, high blood-fat levels, low HDL cholesterol levels, and insulin resistance," he says. "Reducing carbs is not only an option, but probably the preferred option for people to correct these abnormalities."
Atkins, Zone, Ornish Diets Made Easy
Gardner says he thinks the main reason people trying to follow the Atkins diet lost more weight is that the diet is easy to understand.
WebMD asked Sears and Ornish whether they could sum up their diets in a brief, simple statement.
"For the Zone diet, a person needs only one hand and one eye," Sears says. "At every meal, the rest of your life, divide your plate into three equal parts. On one, put a piece of meat, fish, chicken, tofu, or low-fat protein no wider or thicker than the palm of your hand. And on the other two thirds of your plate, fill it full of vegetables and fruits. And then take a dash of monounsaturated, healthy fat. And now you have a meal with the right balance of carbohydrate, protein, and fat. That is how you lose weight -- you keep hunger and satiation under control."
Ornish says simple changes to the diet help people lose weight and gain health.
"These changes are simple," he says. "Eat less total fat. Eat fewer simple carbs. Try to eat whole foods if you can -- predominantly fruits and vegetables and whole grains and legumes in their natural form. And eat some fish."
Brownell says it obviously isn't easy to lose weight, or else all sensible diet plans would work better.
"Obesity is a problem that screams out to be prevented rather than treated," he says. "We need to start with people when they are children, and we need to work on preventing the problem."