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.

Average Weight Loss Unimpressive

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 two 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.

No Significant Differences Among Diets

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 one 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.

"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," the authors write.

Adherence Is Critical

"[W]e 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," the authors note, adding that no single diet produced satisfactory adherence rates.

"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," say the authors.

"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.