Four Popular Diets Equally Effective for Weight Loss

Peggy Peck

November 10, 2003

Nov. 10, 2003 (Orlando) -- In a randomized study comparing four popular diets over the course of a year, all diets demonstrated efficacy for weight loss and reduction of Framingham risk scores, but only the Atkins, Weight Watchers, and Zone diets achieved statistically significant reductions in Framingham scores, according to results presented here at the American Heart Association (AHA) Scientific Sessions.

"Losing 20 pounds corresponded to about a 30% reduction in heart risk score," said Michael L. Dansinger, MD, assistant professor of medicine at Tufts University, New England Medical Center, in Boston, Massachusetts. Although he explained that at this point "it isn't clear if a 30% reduction in risk score is the same as a 30% reduction in heart attacks." Dr. Dansinger presented his results at an AHA press conference.

Patients were evenly assigned to the Atkins (low carbohydrates), Zone (moderate carbohydrates), Ornish (low-fat vegetarian), or Weight Watchers (moderate fat) diet and told to follow the diet "to the best of their ability for two months," he said. Patients were given official diet cookbooks and assigned to small group classes for diet education. For the remaining 10 months, the volunteers were told to follow their assigned diet "to whatever extent they wanted." The study "evaluated only the food program, not any additional lifestyle modifications such as meditation or exercise," he said.

Following the diets was not easy, Dr. Dansinger said, noting that the drop-out rate for each diet was 22% at two months and by 12 months half of the volunteers assigned to Atkins or Ornish had dropped out, as had 35% of those assigned to Weight Watchers or Zone diets.

For those who stuck with the diet for 12 months, reductions in weight and Framingham risk score were 3.9% and 12.3% for Atkins (n=21; 52% completion), 6.2% and 6.6% for Ornish (n=20; 50% completion), 4.5% and 14.7% for Weight Watchers (n=26; 65% completion), and 4.6% and 10.5% for Zone (n=26; 65% completion). All diets resulted in significant ( P < .05) weight loss from baseline and all but the Ornish diet ( P = .013) resulted in significant reductions in the Framingham risk score, he said.

Dr. Dansinger told Medscape that this does not mean that the "Ornish diet doesn't reduce heart disease risk. I have great faith in the Ornish diet, but it did not meet the statistical test in this study."

Dean Ornish, MD, founder and president of the Preventive Medicine Research Institute in Sausalito, California, was immediately critical of the results. Dr. Ornish told Medscape that the people assigned to his diet "lost more weight, had greater reductions in low-density lipoprotein (LDL) cholesterol, and were the only dieters to significantly lower insulin -- even though the Atkins and Zone diets claim to be specifically designed to lower insulin."

Dr. Dansinger, who joined Dr. Ornish in fielding questions from reporters, agreed that the Ornish diet posted impressive results for those who stayed the course for a year: a 19.9% reduction in insulin levels while the Atkins diet reduced insulin by 7.7%, Weight Watchers by 8.8%, and the Zone by 16.5%. Likewise, the Ornish diet reduced LDL cholesterol by 16.7%, while the Atkins diet reduced LDL by 8.6%, followed by Weight Watchers dieters at 7.7%, and Zone dieters achieved a 6.7% drop in LDL cholesterol.

But the heart disease risk score is based on the high-density lipoprotein (HDL)/LDL ratio, and the "Ornish diet does not increase HDL, while the other diets do achieve significant increases in HDL," said Dr. Dansinger. Weight Watchers increased HDL cholesterol by 18.5%, while the Atkins and Zone diets increased HDL by 15.4% and 14.6%, respectively. But the Ornish diet increased HDL by just 2.2%.

Dr. Ornish said HDL cholesterol is not really a factor because "HDL is really like a garbage truck that goes around picking up the garbage, which is bad cholesterol. When you don't have as much bad cholesterol -- garbage -- you don't need as many garbage trucks." He added, "Raising HDL is easy: eat a stick of butter. That will drive up your HDL, but it's not good for you."

Dr. Dansinger said HDL is a little more complicated. For example, "exercise increases HDL and we do think that low HDL is a risk factor," he said.

"The good news about this study is that we have demonstrated that all these diets work. That means that physicians can work with patients to select the diet that is best suited to the patient. For example, if you have a patient who likes meat, it is unlikely that he or she will comply with the Ornish diet," said Dr. Dansinger.

"In the short run, I think weight loss trumps everything," said Robert H. Eckel, MD, chair of the American Heart Association's Nutrition, Physical Activity, and Metabolism Council and professor of medicine at the University of Colorado Health Sciences Center in Denver. "If you lose weight, it doesn't matter how you lose it. But in the long run we don't know the effect of the macronutrients that you are eating." Dr. Eckel was not involved in the study.

The study was funded by a National Institutes of Health grant, the Tufts-New England Medical Center, and the U.S. Department of Agriculture Nutrition Research Center at Tufts.

AHA 2003 Scientific Sessions: Abstract 3535. Presented Nov. 12, 2003.

Reviewed by Gary D. Vogin, MD

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