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A to Z: A Comparative Weight Loss Study of the Atkins, Zone, Ornish, and USDA/LEARN Diets

Obesity is the single most significant nutrition-related health issue of the new millennium. Several "medical experts" have challenged the National dietary weight loss guidelines (low in fat, high in carbohydrate) and have designed and promoted diets that dramatically differ from one another, mostly low-carbohydrate diets. These diets have become very popular among Americans, despite a lack of scientific evidence supporting their claims. The aim of this study was to examine the effects of 4 diets, representing a spectrum of carbohydrate intake, on weight loss and related metabolic variables in overweight and obese premenopausal women.

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Eligible Participants

  • Generally healthy women, 25 to 50 years of age
  • Overweight or obese

Study Design

Three hundred and eleven women were randomized to follow the diet from one of 4 popular diet books for 1 year: Dr. Atkins' New Diet Revolution, Enter the Zone, The LEARN Manual for Weight Management, or Eat More, Weigh Less by Ornish. These diets comprised a wide range of carbohydrate intake, from the lowest in the Atkins Diet to the highest in the Ornish diet. Participants attended 1-hour classes led by a registered dietitian once per week for 8 weeks and covered approximately one eighth of their respective books per class. Each group received specific target goals according to the emphasis of the assigned diet. Participants completed a clinic visit at the beginning of the study and after 2, 6, and 12 months to assess weight and other anthropometric data, and provide blood samples to measure markers of cardiometabolic risk.

Conclusions

The women assigned to follow the Atkins diet, which had the lowest carbohydrate intake, lost more weight and experienced more favorable metabolic effects after 1 year than the women assigned to the Zone, Ornish, or LEARN diets. Although the weight loss in the Atkins group was greater than that of other groups, the magnitude of weight loss was modest, with a mean 12-month weight loss of about 10 pounds.

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