Popular Diets have become increasingly prevalent and controversial.1 More than 1000 diet books are now available,2 with many popular ones departing substantially from mainstream medical advice.3 Cover stories for major news magazines, televised debates, and cautionary statements by prominent medical authorities4,5 have fueled public interest and oncern regarding the effectiveness and safety of such diets.6-8 Although some popular diets are based on long-standing medical advice and recommend restriction of portion sizes and calories (eg, Weight Watchers),9 a broad spectrum of alternatives has evolved. Some plans minimize carbohydrate intake without fat restriction (eg, Atkins diet),10 many modulate macronutrient balance and glycemic load (eg, Zone diet),11 and others restrict fat (eg, Ornish diet).12 Given the growing obesity epidemic,13 many patients and clinicians are interested in using popular diets as individualized eating strategies for disease prevention.14 Unfortunately, data regarding the relative benefits, risks, effectiveness, and Context The scarcity of data addressing the health effects of popular diets is an important public health concern, especially since patients and physicians are interested in using popular diets as individualized eating strategies for disease prevention.
Objective To assess adherence rates and the effectiveness of 4 popular diets (Atkins, Zone, Weight Watchers, and Ornish) for weight loss and cardiac risk factor reduction.
Design, Setting, and Participants A single-center randomized trial at an academic medical center in Boston, Mass, of overweight or obese (body mass index: mean,35; range, 27-42) adults aged 22 to 72 years with known hypertension, dyslipidemia, or fasting hyperglycemia. Participants were enrolled starting July 18, 2000, and randomized to 4 popular diet groups until January 24, 2002.
Intervention A total of 160 participants were randomly assigned to either Atkins(carbohydrate restriction, n=40), Zone (macronutrient balance, n=40), Weight Watchers(calorie restriction, n=40), or Ornish (fat restriction, n=40) diet groups. After 2 months of maximum effort, participants selected their own levels of dietary adherence.
Main Outcome Measures One-year changes in baseline weight and cardiac risk factors, and self-selected dietary adherence rates per self-report.
Results Assuming no change from baseline for participantswhodiscontinued the study, mean (SD) weight loss at 1 year was 2.1 (4.8) kg for Atkins (21 [53%] of 40 participants completed, P=.009), 3.2 (6.0) kg for Zone (26 [65%] of 40 completed, P=.002), 3.0(4.9) kg for Weight Watchers (26 [65%] of 40 completed, P_.001), and 3.3 (7.3) kg for Ornish (20 [50%] of 40 completed, P=.007). Greater effects were observed in study completers.
Each diet significantly reduced the low-density lipoprotein/high-density lipoprotein (HDL) cholesterol ratio by approximately 10% (all P_.05), with no significant effects on blood pressure or glucose at 1 year. Amount of weight loss was associated with selfreported dietary adherence level (r=0.60; P_.001) but not with diet type (r=0.07; P=.40). For each diet, decreasing levels of total/HDL cholesterol, C-reactive protein, and insulin
were significantly associated with weight loss (mean r=0.36, 0.37, and 0.39, respectively)with no significant difference between diets (P=.48, P=.57, P=.31, respectively).
Conclusions Each popular diet modestly reduced body weight and several cardiac risk factors at 1 year. Overall dietary adherence rates were low, although increased adherence was associated with greater weight loss and cardiac risk factor reductions for each diet group.