Low-Carb Atkins Pulls Ahead in Four-Diet Face-Off

STANFORD, Calif., March 6 -- Women who followed the low-carbohydrate, high-protein Atkins diet for a year lost more weight than women assigned to three other diets with a high or higher carbohydrate intake, researchers here reported.

Furthermore, in the randomized trial of 311 overweight or obese premenopausal women, the Atkins dieters had more favorable overall metabolic effects, including lipid levels, fasting insulin and glucose levels, and systolic blood pressure, Christopher Gardner, Ph.D., of Stanford, and colleagues reported in the March 7 issue of the Journal of the American Medical Association.

The four diets, representing a spectrum of low to high carbohydrate intake, included the Atkins diet (very low in carbohydrates), the Zone diet (low in carbohydrates), the Ornish diet (high in carbohydrates), and the LEARN diet (Lifestyle, Exercise, Attitudes, Relationships, and Nutrition; low in fat, high in carbohydrates, based on national guidelines).

Participants in the 12-month U.S. trial, from February 2003 to October 2005, were recruited from the local community, primarily through media advertisements. The trial included women with a body mass index ranging from 27 to 40 kg/m².

Participants were randomly assigned to follow the Atkins (n=77), Zone (n=79), LEARN (n=79), or Ornish (n=76) diets and received weekly instruction for two months, and then an additional 10-month follow-up.

In addition to weight loss, secondary outcomes included a lipid profile (LDLs, HDLs, non-high-density lipoprotein, and triglyceride levels), percentage of body fat, waist-hip ratio, fasting insulin and glucose levels, and blood pressure.

Weight loss of about 10 pounds, although modest, was greater for women in the Atkins diet group compared with the other diet groups at 12 months. However, mean 12-month weight loss was significantly different for only the Atkins and Zone diets (P

Concerns that a diet high in total and saturated fat would adversely affect blood lipid levels and cardiovascular risk were not substantiated in this 12-month study, the researchers wrote. However, they said, it could not be determined whether the benefits could be attributed specifically to the low carbohydrate intake versus other aspects of the diet, such as the high protein intake.

Further examination of the dietary effects on lipid variables would benefit from analyses of lipoprotein particle subfractions and follow-up longer than 12 months, Dr. Gardner's team wrote.

In discussing other recent weight-loss trials, the researchers said that substitution of either protein for fat while holding carbohydrates constant or protein for carbohydrates while holding fat constant, produced improvement in weight loss, triglycerides, HDLs, and increased satiety in the higher protein diets.

Therefore, the effects of the current study, the researchers said, should be interpreted as resulting from the combination of macronutrient changes that follow low-carbohydrate versus high carbohydrate diets, and not just changes in carbohydrates alone.

Among the study's limitations, the researchers wrote that weight-loss trajectories had not stabilized at 12 months, suggesting that longer follow-up would likely have resulted in progressively diminished group differences.

Other limitations included lack of assessment of individual adherence to the diets, and the lack of assessment of satiety.

While questions remain about long-term effects and mechanisms in this weight-loss study, these finding have important implications for clinical practice and health care policy, the researchers said.

Physicians whose patients want to use a low-carbohydrate diet can be reassured that weight loss is likely to be at least as large as for any other dietary pattern and that the lipid effects are unlikely to be of immediate concern, the investigators wrote.

"As with any diet, physicians should caution patients that long-term success requires permanent alterations in energy intake and energy expenditure, regardless of macronutrient content," they concluded.