Gardner CD, Kiazand A, Alhassan S, Kim S, Stafford RS, Balise RR, Kraemer HC, King AC

JAMA. 2007;297:969-977.

Context

Popular diets, particularly those low in carbohydrates, have challenged current recommendations advising a low-fat, high-carbohydrate diet for weight loss. Potential benefits and risks have not been tested adequately.

Objective.

To compare 4 weight-loss diets representing a spectrum of low to high carbohydrate intake for effects on weight loss and related metabolic variables.

Design, Setting, and Participants.

Twelve-month randomized trial conducted in the United States from February 2003 to October 2005 among 311 free-living, overweight/obese (body mass index, 27-40) nondiabetic, premenopausal women.

Intervention.

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 2 months, then an additional 10-month follow-up.

Main Outcome Measures.

Weight loss at 12 months was the primary outcome. Secondary outcomes included lipid profile (low-density lipoprotein, high-density lipoprotein, and non-high-density lipoprotein cholesterol and triglyceride levels), percentage of body fat, waist-hip ratio, fasting insulin and glucose levels, and blood pressure. Outcomes were assessed at months 0, 2, 6, and 12. The Tukey studentized range test was used to adjust for multiple testing.

Results.

Weight loss was greater for women in the Atkins diet group compared with the other diet groups at 12 months, and mean 12-month weight loss was significantly different between the Atkins and Zone diets (P < .05). Mean 12-month weight loss was as follows: Atkins, -4.7 kg (95% confidence interval [CI], -6.3 to -3.1 kg), Zone, -1.6 kg (95% CI, -2.8 to -0.4 kg), LEARN, -2.6 kg (-3.8 to -1.3 kg), and Ornish, -2.2 kg (-3.6 to -0.8 kg). Weight loss was not statistically different among the Zone, LEARN, and Ornish groups. At 12 months, secondary outcomes for the Atkins group were comparable with or more favorable than the other diet groups.

Conclusions.

In this study, premenopausal overweight and obese women assigned to follow the Atkins diet, which had the lowest carbohydrate intake, lost more weight and experienced more favorable overall metabolic effects at 12 months than women assigned to follow the Zone, Ornish, or LEARN diets. While questions remain about long-term effects and mechanisms, a low-carbohydrate, high-protein, high-fat diet may be considered a feasible alternative recommendation for weight loss.

Editor's Comment.

This is the most recent of several studies that have evaluated the effects of low-carbohydrate diets versus other types of diet and their effects on weight loss and cardiovascular risk factors. Gardner et al have designed and carried out an excellent study of 4 popular diets using weight and body composition, as well as lipids, blood pressure, insulin, and glucose. The retention rate for the all groups was 80%. The results showed that the Atkins diet group had significantly greater weight loss than only the Zone diet group after 12 months and that the Atkins diet did not negatively affect cardiovascular risk factors. On the contrary, changes in both high-density lipoprotein (HDL) and triglycerides favored Atkins. A closer reading of this study (a challenging task because of the complexity of the design and data presentation) provides some interesting insight for clinicians. First, over 12 months, the total weight loss (2%-5%) ranged from 3.5 to 10 lb. Positive changes in risk factors were found after 12 months for HDL, triglycerides, and systolic and diastolic blood pressure. The take home points for clinicians include the following: (1) all of these diets worked when people adhered; (2) none of the diets negatively affected the cardiovascular risk factors studied; (3) positive changes in HDL, triglycerides, and blood pressure resulted from the diet and/or the weight loss; (4) although Atkins was significantly better at the 12-month period, the real differences between these diets is probably small, but losing even minimal amounts of weight is positive; and (5) restricting refined carbohydrates may be beneficial in weight loss programs. Finally, it seems clear that none of the groups adhered closely to their dietary guidelines, that dietary behavior is very difficult to change, and that weight management programs are difficult to manage successfully.

JR