Overweight and obese premenopausal women lost more weight and showed more favorable metabolic changes after 1 year on the Atkins diet than did those who followed the Zone, LEARN, or Ornish diets, investigators have reported.
Women who followed the high-protein, high-fat, low-carbohydrate Atkins diet also showed no adverse changes in triglycerides, HDL cholesterol, blood pressure, or insulin resistance, as feared by some critics.
Although questions remain about long-term effects and mechanisms of action, “physicians whose patients initiate 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,” Christopher D. Gardner, Ph.D., and his associates in the A TO Z (Atkins, Traditional, Ornish, Zone) Weight Loss Study wrote in the journal of the American Medical Association.
They cautioned that the magnitude of weight loss was modest at best with all four diets, ranging from 2% to 5% of total weight, and the trajectories of weight loss during the 1-year study indicated that differences in weight loss among the diets would diminish over time.
Dr. Gardner and his associates of Stanford (Calif.) University conducted the A TO Z study to compare the effects of four well-known diets representing a spectrum of carbohydrate intake. The Atkins diet is very low in carbohydrates; the Zone diet is low in carbohydrates; the LEARN (Lifestyle, Exercise, Attitudes, Relationships, and Nutrition) diet, is high in carbohydrates; and the Ornish diet is very high in carbohydrates.
Subjects were 311 women aged 25–50 years, with body mass indices of 27–40 kg/m2, who were randomly assigned to read one of the four diet books and attend eight 1-hour weekly classes during which the books and diets were discussed by a dietitian, and to follow one of the diets. The attrition rate was about 20% and did not differ significantly between diets.
Total energy intake did not differ among the four groups either at baseline or at any point during follow-up, even though two diets (Zone and LEARN) called for caloric restriction and the other two did not. There was a modest increase in physical activity in all groups.
The mean weight loss at 1 year was 4.7 kg for the Atkins diet, 1.6 kg for the Zone diet, 2.2 kg for the LEARN diet, and 2.6 kg for the Ornish diet (JAMA 2007;297:969–77).
There were no significant differences among the groups in percentage of body fat or in waist-to-hip ratio, nor in fasting insulin or fasting glucose levels. The decrease in blood pressure levels paralleled that in weight, with the Atkins group showing slightly larger decreases than the other groups. Triglycerides and HDL cholesterol showed slightly more improvement in the Atkins group, but LDL cholesterol did not.
“The reported effects of the current study should be interpreted as resulting from the combination of macronutrient changes that occur when following low- vs. high-carbohydrate diets, not changes in carbohydrates alone. Greater satiety from the higher protein content of the Atkins diet may have contributed to the benefits observed for that group,” the authors noted.
Triglycerides and HDL cholesterol showed slightly more improvement in women in the Atkins group. Elsevier Global Medical News