STANFORD, CA -- The case for low-carbohydrate diets is gaining weight after a recent comparison of four popular diets published in this week’s issue of the Journal of the American Medical Association.

More than 300 pre-menopausal, non-diabetic, overweight women were randomly assigned to follow either the Atkins, Zone, LEARN (Lifestyle, Exercise, Attitudes, Relationships and Nutrition) or Ornish diet. Researchers chose the four diets to represent the full spectrum of low- to high-carbohydrate diets. Of the more than 300 women in the study, those randomly assigned to follow the Atkins diet for a year not only lost more weight than the other participants, but they also experienced the most benefits in terms of cholesterol and blood pressure. However, the Atkins group also gained back more weight in the second half of the study than those in the three other groups. Women in the Atkins group lost an average of almost 13 pounds after six months, but ended the one-year period with a final overall average loss of 10 pounds.

The Atkins diet, popularized by the 2001 republication of Dr. Atkins' New Diet Revolution, represents the lowest carbohydrate diet. The Zone diet, also low-carbohydrate, focuses on a 40:30:30 ratio of carbohydrates to protein to fat, a balance said to minimize fat storage and hunger. The LEARN diet follows national guidelines reflected in the U.S. Department of Agriculture's food pyramid—low in fat and high in carbohydrates. The Ornish diet, based on bestseller Eat More, Weigh Less by Dean Ornish, is high in carbohydrates and low in fat.

"Many health professionals, including us, have either dismissed the value of very-low-carbohydrate diets for weight loss or been very skeptical of them," says lead researcher Christopher Gardner, PhD, assistant professor of medicine at the Stanford Prevention Research Center. "But it seems to be a viable alternative for dieters."

Study participants in all four groups attended weekly diet classes for the first eight weeks of the study and each received a book outlining the specific diet to which they were assigned. For the remaining 10 months of the study, the women's weight and metabolism were regularly checked, and random phone calls monitored what they were eating.

The $2 million study mimicked real-world conditions, Gardner says. Women in the study had to prepare or buy all their own meals, and not everyone followed the diets exactly as the books laid out, just as in real life.

At the end of a year, the 77 women assigned to the Atkins group lost an average of 10.4 pounds. Those assigned to LEARN lost 5.7 pounds, the Ornish followers lost 4.8 pounds and women on the Zone lost 3.5 pounds, on average. In all four groups, however, some participants lost up to 30 pounds.

After 12 months, women following the Atkins diet, relative to at least one of the other groups, had larger decreases in body mass index, triglycerides and blood pressure. Their good increased more than the women on the other diets.

Gardner has several ideas for why the Atkins diet had the overall best results. The first is the simplicity of the diet. "It's a very simple message," he says. "Get rid of all refined carbohydrates to lose weight." This message directly targets a major concern with the American diet right now—the increasing consumption of refined sugars in many forms, such as high-fructose corn syrup.

Beyond pinpointing this high sugar intake, the Atkins diet does the best at encouraging people to drink more water, he says. And when people replace sweetened beverages with water, they don't generally eat more food; they simply consume fewer calories over the course of the day.

The third theory Gardner offered as to why the Atkins diet was more successful is that it is not just a low-carbohydrate diet, but also a higher protein diet. "Protein is more satiating than carbohydrates or fats, which may have helped those in the Atkins group to eat less without feeling hungry," he says.

Though critics of low-carbohydrate diets say that such diets can lead to health problems, none of the factors measured in this study was worse for the Atkins group. However, potential long-term health problems that could not have been identified in a 12-month study may exist, Gardner says. Also, several basic vitamins and minerals can be difficult to get in adequate amounts from a very-low-carbohydrate diet.

More research is needed, Gardner says. He hopes to use the large data set generated in this study to investigate why different diets might work better for different people.

"We're trying to see if we can learn more about the factors that predict success and failure with weight loss," he says.