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E-Newsletter No. 56

Every week, it seems that somebody publishes another diet book that claims to present the best method for losing weight and keeping it off. In fact, there are very few data addressing the health effects of popular diets and even fewer data that directly compare different diets. In this randomized trial, investigators enrolled 160 overweight or obese adults (mean body mass index, 35) ages 22 to 72 with known hypertension, dyslipidemia or fasting hyperglycemia. Subjects were randomized (concealed allocation assignment) to either Atkins (carbohydrate restriction), Ornish (fat restriction), Weight Watchers (caloric restriction) or Zone (macronutrient balance) diet groups. Individuals assessing outcomes were blinded to treatment group assignment. The study attrition rate as a result of patient dropouts was high: The number of participants who did not complete the study at months 2, 6, and 12 were 34 (21%), 61 (38%), and 67 (42%), respectively. The most common reason cited by subjects for withdrawing was that the assigned diet was too hard to follow or was not resulting in enough weight loss. Although the difference was not statistically significant (P=.08), more subjects discontinued the Atkins (48%) and Ornish (50%) diets than the less extreme Zone (35%) and Weight Watchers (35%) diets. According to intention-to-treat analysis, all four diets resulted in statistically similar weight loss at one year. In each of the diet groups, about 25% and 10% of the subjects sustained a weight loss of more than 5% and 10% of initial body weight, respectively, at one year. Cardiac risk factor improvement was directly proportional to the amount of weight loss and was similar among the diet groups. Self-reported dietary adherence directly correlated with the amount of weight loss and reduction in cardiac risk factors. The study was powered to have and 80% chance of detecting a weight change of 2% from baseline or a 3% difference between diets.


All four popular diets (Atkins, Zone, Ornish, and Weight Watchers) are equally effective for helping adults lose weight and reduce cardiac risk factors. Since success in this study directly correlated with adherence to the diet, it makes sense to help patients choose the diet that is easiest for them to follow, and not to preferentially encourage one diet over any other

Dansinger ML, Gleason JA, Griffith Sl, et al. Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial. JAMA, 2005: 293:43-53

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