Researchers at Brigham and Women's Hospital in Boston, Mass., found in a study of 322 obese subjects that the so-called Mediterranean diet -- a diet plan characterized by high levels of healthy fats, fruits, and vegetables -- beat out the low-fat diet both in terms of how much weight patients lost, as well as how many health benefits they gained as a result of the diet.
To determine this, researchers put study subjects on one of three diet regimens: a low-carb diet, a low-fat diet or a Mediterranean diet. Those on the low-carb diet lost the most weight in two years -- about 12 pounds -- while those on the Mediterranean diet lost about 10 pounds.
And in a finding that may surprise some, those on the low-fat diet lost the least weight -- about seven pounds after two years.
Moreover, researchers found that a low-fat diet bestowed the least health benefits on the dieters compared with the Mediterranean and low-carb diets. Those on the Mediterranean diet were most likely to have improvements in blood sugar levels, while those on the low carb diet had the most improvement in cholesterol levels.
Lead study investigator Dr. Meir Stampfer, co-chair of Brigham and Women's Hospital's Channing Laboratory, said the study provides hard evidence that a low-fat diet is not necessarily the best diet.
"[The] main findings are that low-carb -- as long as the protein and fat sources are healthful -- and Mediterranean diets are good, and even preferential diets for weight loss, and they are safe," Stampfer said.
But some diet experts went so far as to say that the study provides further evidence that one of the biggest misconceptions about dieting is that dietary fat is anathema if you want to achieve the best results.
"The common misconception that low-carbohydrate, high-fat diets raise blood cholesterol is shown, again, not to be true," said Dr. Eric Westman, director of the Lifestyle Medicine Clinic at the Duke University Medical Center. "In fact, the diet with the highest amount of fat [the Mediterranean diet] lowered the total cholesterol/HDL ratio the most!"
Moreover, Dr. Paul Shekelle, director of the Southern California Evidence-Based Practice Center at the RAND Corporation, said that in his own experience he has found that the Mediterranean diet is the one that dieters are more likely to stick with for an extended period of time.
"The Mediterranean diet is the one I find patients are most likely to maintain long-term compliance with," Shekelle said, adding that the low-carb, high-protein diet commonly known as the "Atkins" diet is the one that dieters have the hardest time sticking to.
"If any primary care physician … has a patient on the Atkins diet two years on, you should probably find that patient and … find out how they did it," Shekelle explained. "I've not seen anyone in my practice who is still on the diet two years later. Compliance past a few months is the number one problem with the Atkins diet."
Low-Fat Diet Proponents Fire Back
But some experts said that because of the specific diet plans used in the study, the results are far from conclusive in determining the "best diet."
"The study has important technical flaws," said Dr. Neal Barnard, founder and president of the Physicians Committee for Responsible Medicine. Specifically, Barnard pointed to the study's use of a "low-fat" diet plan, "which is not low in fat at all."
Rather than a traditional low-fat diet plan -- such as the Ornish Diet, which designates that only 10 percent of calories should be derived from fat -- researchers assigned subjects in the low-fat diet group to a plan based on the American Heart Association guidelines, which derives 30 percent of its calories from fat.
According to Barnard, the heart association guidelines for a low-fat diet are "very similar to the current U.S. average" for the amount of calories derived from fat in a diet.
"I fear that this study will be reported as a reason to load on the fat and cholesterol," Barnard explained. "In truth, none of the groups actually followed a low-fat regimen."
In addition, some experts pointed out that the low-fat diet did not meet the traditional goal of increasing carbohydrate and fiber intake, which is required in order to see any weight loss or cholesterol-lowering benefits of the diet.
"I do not think the diets met the stated goals; the 'low-fat' diet did not change the percent of fat in the diet or increase the carbs, as would be expected," said Dr. James Anderson, professor emeritus of medicine and clinical nutrition at the University of Kentucky. "It is difficult for me to draw conclusions from this study."
Individual Approach Best
But regardless of the shortcomings of this research based upon the specific diet plans used in the study, many experts say there is still a great deal of good information to be taken away from this.
Dr. David L. Katz, director of the Prevention Research Center at the Yale University School of Medicine, said the study highlights that weight loss can be achieved in a number of different ways, and rather than focusing on one single diet plan, the better approach is to take the best elements of each diet and combine them into a plan that works for the individual with specific health needs.
"We can do better than a beauty pageant approach to diet and weight loss, and actually pull together what we know about diet and good health," Katz explained. "Sure, cut some carbs -- but only refined starches and simple sugars. Sure, cut some fat -- but focus on trans fat and saturated fat. Sure, adopt a Mediterranean diet, but go easy on the refined pasta or white bread, and be sure to control calories."