Study Finds That Adherence To Diet, Not Type Of Diet, More Important Factor For Losing Weight

Popular diets have become increasingly prevalent and controversial, according to background information in the article. Many popular plans depart substantially from mainstream medical advice, and the effectiveness and safety of these diets have been questioned. Data regarding the relative benefits, risks, effectiveness, and sustainability of popular diets have been limited.

In this one year study, Michael L. Dansinger, M.D., of Tufts-New England Medical Center, Boston, and colleagues assessed adherence rates and the effectiveness of four popular diets for weight loss and cardiac risk factor reduction. The diets and their principle weight loss strategies were: Weight Watchers (restriction of portion sizes and calories); Atkins (minimize carbohydrate intake without fat restriction); Zone (modulate macronutrient balance and glycemic load); and Ornish (restrict fat).

This trial included 160 overweight or obese adults aged 22 to 72 years, with known hypertension, dyslipidemia (high cholesterol), or fasting hyperglycemia (high blood sugar). Participants were enrolled starting July 18, 2000, and randomized to the diet groups until January 24, 2002. Forty participants were assigned to each of the diet plans. After 2 months of maximum effort, participants selected their own levels of dietary adherence.

Assuming no change from baseline for participants who discontinued the study, the researchers found that average weight loss at 1 year was 4.6 lbs. for Atkins (21 [53 percent] of 40 participants completed), 7.1 lbs. for Zone (26 [65 percent] of 40 completed), 6.6 lbs. for Weight Watchers (26 [65 percent] of 40 completed), and 7.3 lbs. for Ornish (20 [50 percent] of 40 completed). Greater effects were observed in study completers. Each diet significantly reduced the low-density lipoprotein/high-density lipoprotein (HDL) cholesterol ratio by approximately 10 percent with no significant effects on blood pressure or glucose at 1 year. Amount of weight loss was associated with self-reported dietary adherence level but not with diet type.

For each diet, decreasing levels of total/HDL cholesterol, C-reactive protein, and insulin were significantly associated with weight loss with no significant difference between diets.

"… all 4 diets resulted in modest statistically significant weight loss at 1 year, with no statistically significant differences between diets," the authors write. "In each diet group, approximately 25 percent of the initial participants sustained a 1-year weight loss of more than 5 percent of initial body weight and approximately 10 percent of participants lost more than 10 percent of body weight."

"… we found that a variety of popular diets can reduce weight and several cardiac risk factors under realistic clinical conditions, but only for the minority of individuals who can sustain a high dietary adherence level. Despite a substantial percentage of participants who could sustain meaningful adherence levels, no single diet produced satisfactory adherence rates and the progressively decreasing mean adherence scores were practically identical among the 4 diets. The higher discontinuation rates for the Atkins and Ornish diet groups suggest many individuals found these diets to be too extreme. To optimally manage a national epidemic of excess body weight and associated cardiac risk factors, practical techniques to increase dietary adherence rates are urgently needed," the authors write.

"One way to improve dietary adherence rates in clinical practice may be to use a broad spectrum of diet options, to better match individual patient food preferences, lifestyles, and cardiovascular risk profiles. Participants in our study were not allowed to choose their dietary assignment; however we suspect adherence rates and clinical improvements would have been better if participants had been able to freely select from the 4 diet options. Our findings challenge the concept that 1 type of diet is best for everybody and that alternative diets can be disregarded. Likewise, our findings do not support the notion that very low carbohydrate diets are better than standard diets, despite recent evidence to the contrary," the researchers write.

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(JAMA. 2005; 293:43-53. Available post-embargo at www.jama.com)

Editor's Note: This study was supported by grants from the General Clinical Research Center via the National Center for Research Resources of the National Institutes of Health (NIH); by a grant from the NIH; a contract from the U.S. Department of Agriculture; and a contract from the Human Metabolic and Genetics Core Laboratory of the Boston Obesity Nutrition Research Center program. Dr. Dansinger was supported by a grant from the Agency for Healthcare Research and Quality.

Editorial: The Dietary Approach to Obesity - Is It the Diet or the Disorder?

In an accompanying editorial, Robert H. Eckel, M.D., of the University of Colorado at Denver and Health Sciences Center, Aurora, Colo., discusses the findings by Dansinger and colleagues that no one diet plan was found most effective for weight loss.

"It seems plausible that for maintenance of reduced body mass, the right diet needs to be matched with the right patient. Ultimately, a 'nutrigenomic' approach most likely will be helpful. At present, there are no data to help clinicians practicably match a diet to an individual patient's 'diet response genotype.' Even beyond this consideration, and arguably more important, once weight loss of more than several kilograms from baseline weight occurs, a substantial step-up in the amount of physical activity and conscientious monitoring as part of a more comprehensive behavior modification appear particularly important, and likely are much more relevant adaptations than the macronutrient composition of the diet."

"Arguably, the best treatment of obesity is prevention by careful dietary monitoring and lifestyle and choices, along with regular physical activity. Once overweight or obesity develops, however, the best existing evidence points toward heeding the recently released joint lifestyle recommendations of 3 professional organizations: the American Cancer Society, the American Diabetes Association, and the American Heart Association, in which the recommended macronutrient mix is built on evidence that higher intake of fruits and vegetables, whole grains, and fish are associated with reduced incidences of diabetes mellitus, cancer, heart disease, and stroke. Although this dietary approach may lead to only modest weight changes, similar to the popular diets evaluated by Dansinger et al, physicians and other health care professions should teach obese patients that both quality and quantity of the diet are important, and that sustained weight loss may well be possible with the addition of physical activity and behavioral change strategies to a modest but persistent caloric restriction--the 'Low Fad' approach," Dr. Eckel concludes.

(JAMA. 2005; 293:96-97. Available post-embargo at www.jama.com)