The study, by researchers at the Stanford University School of Medicine, which is one of the largest and longest-ever conducted, found that those randomly assigned to follow the Atkins diet for a year, lost more weight than the other participants, but also experienced the most benefits in terms of cholesterol and blood pressure.
Lead researcher Christopher Gardner, PhD, assistant professor of medicine at the Stanford Prevention Research Center, says very-low-carbohydrate diets for weight loss have attracted skepticism and been dismissed by many health professionals, but the diet is a viable alternative.
For the study 311 pre-menopausal, non-diabetic, overweight women were randomly assigned to follow either the Atkins, Zone, LEARN or Ornish diet which were chosen because they represent the full spectrum of low- to high-carbohydrate diets.
The popular Atkins diet represents the lowest carbohydrate diet, the Zone diet is also low-carbohydrate, focusing on a 40:30:30 ratio of carbohydrates to protein to fat, a balance said to minimize fat storage and hunger.
The LEARN (Lifestyle, Exercise, Attitudes, Relationships and Nutrition) diet follows national guidelines reflected in the U.S. Department of Agriculture ™s food pyramid - low in fat and high in carbohydrates, while the Ornish diet, based on bestseller Eat More, Weigh Less by Dean Ornish, is very high in carbohydrates and extremely low in fat.
The women 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.
Over the remaining 10 months of the study, the women's weight and metabolism were regularly checked, and what they were eating was monitored by random phone calls.
Gardner says one of the strengths of the $2 million study was that it reflected real-world conditions, as the women had to prepare or buy all their own meals, and not everyone followed the diets exactly as prescribed in the books.
By the end of the twelve month period the 77 women assigned to the Atkins group had lost an average of 10.4 pounds; those assigned to LEARN lost 5.7 pounds; the Ornish group lost 4.8 pounds and women on the Zone lost 3.5 pounds, on average.
Some participants in all four groups lost up to 30 pounds.
It was also found that the women following the Atkins diet had larger decreases in body mass index (BMI), triglycerides and blood pressure; their high-density lipoprotein, the good kind of cholesterol, increased more than the women on the other diets.
Gardner suggests the Atkins diet had the overall best results because of it's very simple message, "get rid of all refined carbohydrates to lose weight" which is in line with a major concern over the American diet and the increasing consumption of refined sugars.
Gardner also says the Atkins diet is the best at encouraging people to drink more water, 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.
Gardner also suggests that the Atkins diet was more successful because is that it is not just a low-carbohydrate diet, but also a higher protein diet which is more satiating than carbohydrates or fats, and may have helped those in the Atkins group to eat less without feeling hungry.
Despite the fact that the Atkins group led the field in terms of the average number of pounds lost, this group also gained back more weight in the second half of the study than those in the three other groups.
The women in the Atkins group had 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.
Claims that low-carbohydrate diets can lead to health problems, were not substantiated in this study, but Gardner does cautions that potential long-term health problems may not have been identified in a 12-month study as several basic vitamins and minerals can be difficult to get in adequate amounts from a very-low-carbohydrate diet.
Gardner hopes to use the data generated in the study to investigate why different diets might work better for different people, but says regardless of what new insights are revealed, he hopes people realise the importance of eliminating refined carbohydrates from their diet.
Critics of the study however argue that the comparison is unfair because by the end of the study few women were following any of the diets very strictly, although those in the Atkins group came the closest.
They also say the study does not address the issue of the long-term health effects of eating foods which are high in fat.
The study was supported by the National Institutes of Health, and a grant from the Community Foundation of Southeastern Michigan and is published in the March 7 issue of the Journal of the American Medical Association.