Study finds that adherence to diet, not type of diet, more important factor for losing weight

12/29/04

A comparison of four popular diet plans finds that the key to losing weight may not be which diet plan a person picks, but sticking with the plan that is chosen, according to a study in the January 5 issue of JAMA. The study also found that popular diets can be effective for modest weight loss and reducing several cardiac risk factors, but overall adherence rates were low.

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.

Source: Eurekalert & others

Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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