JAMA. 2005;293(1):43-53.
Background
Popular diets have become increasingly prevalent and controversial. Although some are based on long-standing recommendations regarding portion control, others depart substantially from mainstream medical advice. With the growing epidemic of obesity, there is interest from both patients and clinicians to use these diets on an individualized basis. However, there is paucity of data regarding the health effects of these popular diets.
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.
Methods
Overweight or obese adults aged 22 to 72 years with known hypertension, dyslipidemia, or fasting hyperglycemia were randomized to 4 popular diets for 1 year. The Atkins group aimed for less than 20 g of carbohydrate daily, with a gradual increase to 50 g daily. The Zone group aimed for a 40%, 30%, and 30% balance of calories from carbohydrate, fat, and protein, respectively. The Weight Watchers group aimed to keep total daily "points" in a range determined by current weight. The Ornish group aimed for a vegetarian diet containing 10% of calories from fat. Subjects were given standardized recommendations regarding exercise and supplements. Subjects were asked to follow their assigned diets to the best of their ability for 2 months, after which they can follow their assigned diets according to their own self-determined interest. Dietary adherence was determined by use of food records and dietary adherence scales. Outcomes were measured at baseline, 2, 6, and 12 months; study personnel were blinded to the dietary assignments of the participants.
Results
One hundred sixty participants were enrolled, with 40 subjects assigned to each diet group. The 4 groups were well matched with regards to baseline characteristics. Mean age was 49 years, and 51% were women. At 12 months, 42% of the participants did not complete the study. There was a nonsignificant trend toward higher discontinuation rates for the more extreme diets (48% for Atkins and 50% for Ornish) as compared with the moderate diets (35% for Zone and 35% for Weight Watchers). The most common reasons cited for stopping were that the assigned diet was too hard to follow or was not yielding enough weight loss. All 4 diets resulted in modest statistically significant weight loss at 1 year, with no difference between groups. There was a strong curvilinear association between self-reported dietary adherence and weight loss. All diets reduced mean low-density lipoprotein cholesterol at 1 year, although this did not reach statistical significance for the Atkins group. All diets significantly increased mean high-density lipoprotein cholesterol, except in the Ornish group. No diet significantly altered triglycerides, blood pressure, or fasting glucose levels. However, the lower-carbohydrate diets (Atkins and Zone) were more likely to reduce triglycerides, diastolic blood pressure, and insulin levels in the short term. All diets reduced 1-year C-reactive protein levels, although this did not reach statistical significance in the Zone group. The amount of weight loss predicted the level of improvement in several cardiac risk factors. There were no diet-related adverse or serious adverse events observed during the study.
Discussion
This study demonstrated 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. Cardiac risk factor reductions were associated with weight loss regardless of the diet type. Hence, sustained adherence to a diet rather than the diet type was the key determinant of health benefits. 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.
Comment
Rather than demonizing some of these popular diets, we as healthcare providers should understand that these "fad diets" are out there and that our patients need guidance regarding them. One possibility is to investigate the notion of using these diets to "jump-start" weight loss under supervision by a healthcare professional. Subsequent weight maintenance can then be individualized on the basis of healthier macronutrient mixes, patient preference, and specific needs. The dismal dietary adherence as well as the modest weight loss results shown in this study highlight the practical difficulties of trying to reverse obesity once it is present. Hence, corollary to efforts to reduce risk in overweight and obese patients, we should also be focusing on the prevention of weight gain in the general population.