Recent trials indicate that low-carbohydrate, nonenergy-restricted diets are at least as effective as traditional low-fat, high-carbohydrate diets in promoting weight loss for up to a year. These trials were, however, limited in many respects. The A TO Z (Atkins, Traditional, Ornish, Zone Weight Loss Study compared four diets representing a wide range of carbohydrate intake in 311 overweight or obese premenopausal women 25 to 50 years of age. The participants had a body mass index (BMI) of 27 or higher but were not diabetic. They received instruction weekly for the first 2 months of the l2-month trial and were randomly assigned to follow one of four diets: Atkins (very low in carbohydrate); Zone (low in carbohydrate); LEARN (Lifestyle, Exercise, Attitudes, Relationships, and Nutrition, a diet low in fat and high in carbohydrate); or Ornish (very high in carbohydrate).
At no time was total energy intake different in the various groups, but reported energy intake decreased significantly relative to baseline. Mean weight loss over 12 months was greater for the Atkins group (4.7 kg) than for the Zone (1.6 kg), LEARN (2.2 kg), or Ornish (2.6 kg) groups. The difference between the Atkins and Zone groups was statistically significant. Changes in BMI, percentage body fat, and waist–hip ratio paralleled those in body weight. Changes in high-density lipoprotein cholesterol and triglycerides favored the Atkins group at all follow-up intervals. Mean blood pressure levels declined most markedly in the Atkins group at all intervals.
Not only was the Atkins diet more effective than the other three diets tested in these overweight or obese premenopausal women, but it also had more favorable metabolic effects. Concern over possible adverse metabolic effects from this low-carbohydrate, high-protein, high-fat diet was not confirmed. Regardless of which diet is tried, patients should know that long-term success requires permanent changes in energy intake and energy expenditure.