4 Popular Diets Tested
Nov. 10, 2003 (Orlando, Fla.) -- Pound for pound, four very popular weight loss diets are all good for shedding weight and lowering the risk of heart disease, say researchers, with one important caveat: You have to stick with the diets, not just start them.
The diet scene has heated up in the past year with low-carb and low-fat diets battling it out. But until now no one actually compared four of the most popular diets -- Atkins, Ornish, Weight Watchers and the Zone -- to find out which was really better for weight loss and lowering the risk of a heart disease.
It turns out, says Michael L. Dansinger, MD, assistant professor of medicine at Tufts University, New England Medical Center in Boston, Mass. that as long as the pounds are shed, heart health improves.
"Losing 20 pounds corresponded to about a 30% reduction in heart risk score," he says. Although he explains 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." Dansinger presented his results here at the American Heart Association's Scientific Sessions 2003.
The Contenders
The Atkins diet -- a low-carb diet consisting primarily of protein and fat. In the first two weeks, carbohydrates are severely restricted but then are introduced back into the diet in the form of fiber-rich carbohydrates.
The Ornish diet -- a high-carb, low-fat vegetarian diet of mostly beans, fruits, grains, and vegetables. Dairy products are eaten in moderation and meats are discouraged.
Weight Watchers -- a low-fat, high-carb diet where each food is assigned a point value and participants are allowed a certain number of points per day.
The Zone -- a diet based on a 40-30-30 system where participants eat 40% of their calories from "favorable" carbohydrates such as vegetables and beans, 30% from low-fat proteins, and 30% from unsaturated fats, such as olive and canola oils, nuts, and avocados.
Low-Carb vs. Low-Fat
Dansinger studied 160 overweight men and women who volunteered to participate in a yearlong diet study. Forty volunteers were assigned to each diet, he says. Dansinger says he was "just testing the diets, not any exercise or other lifestyle modifications that are part of the entire diet program." The researchers also calculated a score to estimate a person's heart disease risk -- based on common heart disease risk factors, such as cholesterol and blood pressure.
The benefits from the diets were limited to those who carefully followed them -- and following the diets was no easy task since the drop out rate for each diet was 22% at two months. By one year half of the volunteers assigned to Atkins or Ornish had dropped out as had 35% of those assigned to Weight Watchers or Zone diets.
Participants following the Atkins, Weight Watchers, and Zone diets achieved significant reductions in the heart risk score. Those following the Ornish diet did not show any significant improvement in the heart disease risk score.
Dansinger tells WebMD 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."
Ornish Responds
Dean Ornish, MD, founder and president of the Preventive Medicine Research Institute in Sausalito, Calif., was immediately critical of the results.
Ornish tells WebMD that the people assigned to his diet "lost more weight, had greater reductions in LDL (the 'bad' 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." Lower insulin levels indicate a lower risk of developing diabetes, another powerful heart disease risk factor.
Dansinger, who joined Ornish in fielding questions from reporters, agrees that the Ornish diet posted impressive results for those who stayed the course for a year: a nearly 20% reduction in insulin levels while the Atkins diet dropped insulin by about 8% and the Zone was associated with a 17% drop in insulin.
Likewise, the Ornish diet reduced LDL cholesterol by 17%, while the Atkins dieters reduced LDL by 9%, followed by Weight Watchers dieters at 8% and Zone dieters at 7%.
Good Cholesterol: How Important Is It?
But the heart disease risk score is based on the ratio between LDL cholesterol and HDL "good" cholesterol.
"The Ornish diet does not increase HDL, while the other diets do achieve significant increases in HDL," says Dansinger. The Atkins and Zone diets increased HDL by 15%, while Weight Watchers posted an 18.5% gain. But the Ornish diet increased HDL by just 2.2%.
Ornish says HDL 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 adds, "raising HDL is easy: eat a stick of butter. That will drive up your HDL, but it's not good for you."
Dansinger says HDL is a little more complicated. For example, "exercise increases HDL and we do think that low HDL is a risk factor for heart disease," he says.
"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," says Dansinger.
"In the short run, I think weight loss trumps everything. 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 [carbohydrates, fats, and proteins] that you are eating," says 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. Eckel was not involved in the study.
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