The dietary approach to obesity: is it the diet or the disorder?

INDIVIDUALS SEEKING TO LOSE WEIGHT HAVE MANY DIET choices, ranging from very low-fat (Ornish) to very highfat (Atkins). However, despite great popularity and millions of dollars of sales, good-quality comparative data on the safety and effectiveness of these diets remain elusive. The study by Dansinger et al in this issue of JAMA could be the randomized trial many have been waiting for to help determine which diet works best. Yet, even after considering a number of important limitations, the primary outcome of weight loss at 1 year was modest and there was no difference between the low-carbohydrate approach of Atkins, the high-protein low-glycemic load approach of Sears (the Zone diet), the very low-fat approach of Ornish, and the low-calorie/portion-size approach of Weight Watchers. The results of the study by Dansinger et al appear to be at odds with findings from a number of recent studies that demonstrated more weight loss, at least during the initial months, with low-carbohydrate diets. One important similarity between this trial and the other studies is a high dropout rate. In the study by Dansinger et al, 42% of the study participants were no longer adhering to their diets by 12 months after randomization, and those participants who did complete the trial had a weight reduction of only 5 kg or 5% from baseline weight. Adherence rates were poor for all 4 diets but were particularly poor for the Atkins and Ornish groups. In the setting of a randomized trial, in which there was at least initially substantial involvement of the study team, the results among adherent participants would have been expected to be better. After all, some studies suggest that obese patients can lose weight on their own. Data from the National Weight Control Registry indicate that some patients who successfully lose at least 10% of their weight on their own sustain the reduction for 5 years. However, Heshka et al demonstrated that the dropout rate in a self-help weight loss group was similar to that experienced in a commercial weight loss program, but the amount of weight loss was less in the self-help group. Thus, perhaps more structure and input from health care professionals does facilitate the outcome, at least over relatively short intervals. Even 1 month after randomization in the study by Dansinger et al, adherence to the recommendations of the Atkins, Ornish, and Zone diets was highly variable. Participants in the Atkins diet group were ingesting a median of 68 g of carbohydrate daily, not 20 g as recommended at this stage of the diet. Participants in the Ornish diet group were consuming a median of 27 g of fat or 17% of total calories after 1 month, well above the target of 10%. By 1 year, calories from fat accounted for 32% of total intake. For participants in the Zone diet group, carbohydrate intake accounted for 45% of total calories by 1 month, identical to the target of 45%, while fat content was 34% of calories, slightly above the target of 30%. An additional concern historically related to the dietary treatment of obesity is estimated caloric intake at baseline. The reported average caloric intake was only 2059 kcal for participants whose mean weight was 100 kg (220 lb). This is well below a very conservative estimate of 2860 calories (calculated as basal calories [weight in pounds 10] + lifestyle activity level [weight in pounds 3]) for an individual younger than 50 years who weighs 220 lb with a sedentary lifestyle. Even with a further 10% downward adjustment for an individual aged 50 years or older, the estimated caloric intake of 2574 is more than 25% above the average estimated by this study population (average age of 49 years). This underestimate is not surprising, given that diet records are notoriously inaccurate in obese patients. Losing weight and sustaining weight reduction are very difficult. Most health care professionals who treat obese patients would acknowledge that there is insufficient knowledge about mechanisms for recidivism in obesity. Beyond a lack of willpower is a plethora of biological explanations that challenge the weight-reduced state. These include increased appetite with a preference for energy-dense foods, reductions in energy expenditure (both basal metabolic rate and physical activity), increased insulin sensitivity, increased respiratory quotient due to more carbohydrate oxidation and less fat oxidation, and tissue-specific changes in the activity of lipoprotein lipase (more in adipose tissue and