ATLANTA - The Atkins diet may have proved itself after all: A low-carb diet and a Mediterranean-style regimen helped people lose more weight than a traditional low-fat diet, according to one of the longest and largest studies to compare the dueling weight-loss techniques.
A bigger surprise: The low-carb diet improved cholesterol more than the other two. Some critics had predicted the opposite.
"It is a vindication," said Abby Bloch of the Dr. Robert C. and Veronica Atkins Foundation, a philanthropy group that honors the Atkins' diet's creator and was the study's main funder.
However, all three approaches - the low-carb diet, a low-fat diet, and a so-called Mediterranean diet - achieved weight loss and improved cholesterol.
The study is remarkable not only because it lasted two years, much longer than most, but also because of the huge proportion of people who stuck with the diets - 85 percent.
Researchers approached the Atkins Foundation with the study idea. But the foundation played no role in the design or reporting of the results, said lead author Iris Shai of Ben-Gurion University of the Negev.
Other experts said the study - published today in the New England Journal of Medicine - was highly credible.
"This is a very good group of researchers," Kelly Brownell, chief of Yale University's Rudd Center for Food Policy and Obesity, said.
The research was done in a controlled environment - an isolated nuclear research facility in Israel. The 322 participants got lunch, their main meal of the day, at a central cafeteria.
"The workers can't easily just go out to lunch at a nearby Subway or McDonald's," said Meir Stampfer, the senior author and a professor of epidemiology and nutrition at the Harvard School of Public Health.
In the cafeteria, the foods for each diet were identified with colored dots, using red for low-fat, green for Mediterranean, and blue for low-carb. As for breakfast and dinner, the dieters were counseled on how to stick to their plans and were asked to fill out questionnaires on what they ate, Mr. Stampfer said.
The low-fat diet - no more than 30 percent of calories from fat - restricted calories and cholesterol and focused on low-fat grains, vegetables, and fruits as options. The Mediterranean diet had similar calorie, fat, and cholesterol restrictions, emphasizing poultry, fish, olive oil, and nuts.
The low-carb diet set carb limits but not calories or fat and urged dieters to pick vegetarian sources of fat and protein.
"So not a lot of butter and eggs and cream," said Madelyn Fernstrom, a University of Pittsburgh Medical Center weight management expert who reviewed the study but was not involved in it.
Most participants were men; all men and women in the study got roughly equal amounts of exercise, the study's authors said.
Average weight loss for those in the low-carb group was 10.3 pounds after two years. Those in the Mediterranean diet lost 10 pounds, and those on the low-fat regimen dropped 6.5.
More surprising were the cholesterol measures. Critics have admitted that an Atkins-style diet could help people lose weight but feared that in the long term, it may drive up cholesterol because it allows more fat.
But the low-carb approach seemed to trigger the most improvement in several cholesterol measures, including the ratio of total cholesterol to HDL, the "good" cholesterol. For example, someone with total cholesterol of 200 and an HDL of 50 would have a ratio of 4-1. The optimum ratio is 3.5-1, according to the American Heart Association.
Doctors see that ratio as a sign of a patient's risk for hardening of the arteries. "You want that low," Mr. Stampfer said.
The ratio fell by 20 percent in people on the low-carb diet, compared to 16 percent in those on the Mediterranean, and 12 percent in low-fat dieters.
The study is not the first to offer a favorable comparison of an Atkins-type diet. Research in the Journal of the American Medical Association last year found overweight women on the Atkins plan had slightly better blood pressure and cholesterol readings than those on the low-carb Zone diet, the low-fat Ornish diet, and a low-fat diet that followed U.S. guidelines.
The heart association has recommended low-fat diets to reduce heart risks, but some of its leaders have noted the Mediterranean diet also is safe.
The Atkins-type approach fared less favorably when subgroups such as diabetics and women were examined. Among the 36 diabetics, only those on the Mediterranean diet lowered blood-sugar levels. Among 45 women, those on the Mediterranean diet lost the most weight.