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The A TO Z Study: Examining the Efficacy of Weight Loss Alphabet Soup
By Dónal P. O'Mathúna, PhD, Dr. O'Mathúna is a lecturer in Health Care Ethics, School of Nursing, Dublin City University, Ireland; he reports no consultant, stockholder, speaker's bureau, research, or other financial relationships with companies having ties to this field of study.
Source: Gardner CD, et al. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: The A TO Z Weight Loss Study: A randomized trial. 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 four 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 (BMI 27-40 kg/m2) 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 two months, then an additional 10-month follow-up.
Main Outcome Measures: Weight loss at 12 months was the primary outcome measure. 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 < 0.05). 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 (95% CI, -3.8 to -1.3 kg); and Ornish, -2.2 kg (95% CI, -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. Although questions remain about long-term effects and mechanism of action, a low-carbohydrate, high-protein, high-fat diet may be considered a feasible alternative recommendation for weight loss.
The search for effective ways to lose weight continues. The obesity problem persists in developed countries and is even starting to affect developing countries. A whole business enterprise has developed to promote the diets, books, programs, and supplements that offer people ways to shed the extra pounds. Given the frustration experienced by many, controlled studies evaluating the various approaches are also multiplying. The A TO Z Weight Loss Study adds another trial to those available to help people decide which diet might work best for them.
A TO Z stands for the four diets studied in the trial: Atkins, Traditional, Ornish, and Zone. The Atkins diet is very low in carbohydrate; the Traditional diet is a lifestyle approach that is low in fat, high in carbohydrate, and based on national guidelines; the Ornish diet is very high in carbohydrate; and the Zone diet is low in carbohydrate. This choice reflects recent controversy centered on the carbohydrate content of diets: Are low-carbohydrate diets like Atkins superior to the traditional approach in national guidelines of replacing fat with carbohydrates (and reducing overall calorie intake)?
Controlled studies of different diets have not provided a definitive answer as to which strategy is superior. A meta-analysis published in 2006 reviewed trials that directly compared low-carbohydrate diets with low-fat diets in people with a BMI of at least 25 kg/m2.1 Five studies were included, with between 53 and 132 participants. After six months, those on the low-carbohydrate diets had lost significantly more weight than those on the low-fat diets (on average, 7.3 lbs more). However, by 12 months there were no statistically significant differences in weight loss between the diets.
Significant differences were also found in the lipid profiles, although not consistently favoring one diet type. Total cholesterol and low-density lipoprotein (LDL) levels were lower for those on the low-fat diets (at six and 12 months). For those on the low-carbohydrate diets, total triglyceride was lower (at six and 12 months) and high-density lipoprotein (HDL) was significantly higher (at six months, but not at 12 months).
The A TO Z study was designed to compare larger numbers of participants than previous trials. The study enrolled 311 premenopausal women with a BMI of 27-40 kg/m2. At no point were there significant differences in weight loss between the Ornish, Traditional, or Zone diets. In keeping with previous studies, initial weight loss (at two and six months) was significantly greater on the Atkins diet compared to all the others. However, as usually happens, by 12 months, the differences were no longer significant—except between the Atkins and Zone diets. This change did not arise because of shifts among those on the Ornish or Traditional diets (their overall weight loss remained consistent). Instead, the average weight loss on the Atkins diet decreased between six and 12 months. In other words, people were regaining weight during this time.
The lipid profile changes in the A TO Z study were similar to those found in the meta-analysis, but with some findings more favorable for the low-carbohydrate diet. Total triglyceride was lower and HDL higher at all times for those on the low-carbohydrate diet. Total non-HDL cholesterol levels did not differ between diets at any time. The LDL levels were lower for those on the Ornish and Traditional diets at two months, but not at six or 12 months. These results further substantiate the view that the Atkins diet does not adversely impact cardiovascular health.
It is disappointing that while most studies and reviews of low-carbohydrate and low-fat diets comment that comparisons need to be extended past one year, the A TO Z study followed previous patterns and stopped at 12 months. The long-term effectiveness of low-carbohydrate diets has been an ongoing concern about low-carbohydrate diets. Long-term adherence to these diets is difficult because of the consistent consumption of high-protein foods. The long-term effects of maintaining these diets (or attempting to do so) need to be examined urgently given how many people are attempting to follow their guidelines. Although initial concerns about the impact of low-carbohydrate diets on markers of cardiovascular disease have been ameliorated by controlled studies, concerns about their long-term impact on kidney function remain.
The relatively small number of studies including long-term follow-up demonstrate that a combination of strategies is vital to successful weight loss.2 Reduction in caloric intake is most important. While low-carbohydrate diets lead to more weight loss in the first six months, the goal is reduced caloric intake as part of a diet that people can adhere to for the rest of their lives. Also crucial is increased energy expenditure through some sort of exercise or physical activity. Again, the important factor is activity that becomes part of a person's ongoing lifestyle. Finally, various support programs that provide encouragement for those trying to lose weight and retain a more healthy weight are also important. The A TO Z study, unfortunately, did not add anything to our understanding of those features of weight loss.
1. Nordmann AJ, et al. Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors: A meta-analysis of randomized controlled trials. Arch Intern Med 2006;166:285-293.
2. Wadden TA, et al. Lifestyle modification for the management of obesity. Gastroenterology 2007;132:2226-2238.