STANFORD - A study of four popular diets found that women put on the one with the least carbohydrates -- the Atkins plan -- lost at least twice as much weight as those on the others, researchers reported in a new study.

"Many health professionals, including us, have either dismissed the value of very-low-carbohydrate diets for weight loss or been very skeptical of them," said Christopher Gardner, assistant professor of medicine at the Stanford Prevention Research Center in California, lead author of the study.

"But it seems to be a viable alternative for dieters," he added, for whom the basic message is cutting down as much as possible on refined carbohydrates such as white bread and carbonated drinks.

The research was described as the largest and longest comparison yet done on the four diets.

They were Atkins, the lowest in carbohydrates for the four; the Zone diet, also low in carbohydrates and based on a 40:30:30 ratio of carbohydrates to protein to fat; the Lifestyle, Exercise, Attitudes, Relationships and Nutrition (LEARN) diet which follows U.S. government guidelines for low fat but higher carbohydrates; and the Ornish diet, which is very high in carbohydrates but very low in fat.

The study randomly assigned a group of 311 overweight, post-menopausal, non-diabetic women one of the four diets. All attended weekly diet classes for eight weeks and were given books to follow. Their weight and metabolism were then checked for the following 10 months.

Women assigned to the Atkins group lost an average of 10.4 pounds (4.7 kgs) compared to 5.7 pounds (2.5 kgs) for LEARN, 4.8 pounds (2.1 kgs) for Ornish and 3.5 pounds (1.6 kgs) for Zone, the study said.

The women on the Atkins diet also had the most improvements in terms of cholesterol and blood pressure, added the study published in this week's Journal of the American Medical Association.

The authors said some have worried that diets low in carbohydrates but high in total and saturated fat would cause cholesterol problems and increase the risk of heart disease.

"These concerns have not been substantiated in recent weight-loss diet trials," including the new research, the authors said.

Barry Sears, who developed the Zone diet, criticized the study as "bad science," saying details show the participants did not really follow the diet rules.

"The execution basically was fairly pathetic at best so the conclusions are jaded," he said in an interview. The way people followed the Atkins diet in the study, he said, is actually closer to the Zone's principles.

Study author Gardner, however, said one of the strengths of the $2 million project was that it mimicked real-world conditions, with participants preparing or buying all their own meals and not everyone following the diets exactly.

Gardner said the Atkins diet has "a very simple message. Get rid of all refined carbohydrates to lose weight," thus targeting the increasing consumption of refined sugars, such as high-fructose corn syrup.

He also said the Atkins diet is best at encouraging people to drink more water, and when people replace sweetened drinks with water, they do not generally eat more food.