Choosing a Diet Has No Effect on Weight Loss

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Choosing a Diet Has No Effect on Weight Loss



The opportunity to choose between a low-carbohydrate diet and a low-fat diet did not lead to greater weight loss than simply being assigned to a diet, according to a study publishedin the June 16 issue of the Annals of Internal Medicine. Those assigned a diet lost an average 1.1 kg more than those who chose their diets, but the difference was not statistically significant.
“The doubly randomized preference design of our study allowed us to determine that preference did not meaningfully affect weight loss,” write William Yancy Jr, MD, from the Center for Health Services Research in Primary Care in the Department of Veterans Affairs in Durham, North Carolina, and colleagues. Although they note the limited generalizability of their findings because of their study population, their results combined with previous research findings “converge to suggest that providing a choice of diets to patients does not enhance and may actually hinder weight loss,” the authors write.
At a Veterans Affairs Medical Center, the researchers randomly assigned 207 outpatients, who had a body mass index (BMI) of at least 30 kg/m2, to either choose from one of two diets or be assigned to a diet for a period of 48 weeks. Participants had an average age of 55 years and an average BMI of 36 kg/m2, and 51% were black. The randomization was stratified by sex (27% women), BMI (higher or lower than 40 kg/m2), and type 2 diabetes diagnosis (23% of patients).
Among the 105 patients with the option to choose their diet, 58% chose a low-carbohydrate diet, restricted initially at 20 g carbohydrates per day, with a gradual increase, and 42% chose a low-fat diet, which restricted fat to less than 30% of daily caloric intake. The low-fat diet also restricted saturated fats to less than 10% of daily energy intake, cholesterol to less than 300 mg/day, and total calories to 500 lower than the patient’s daily maintenance energy requirement. Patients could switch their choice at 12 weeks into the study, and five did.
The researchers assigned 52% of the 102 control group participants to the low-carbohydrate diet, and 48% to the low-fat diet.
For the first 24 weeks, group counseling sessions every 2 weeks focused on physical activity and dietary and behavioral topics, such as mindful eating, for all participants. Participants also received pocket guides for counting calories, fat, and carbohydrates and a book and printed handouts for their diet. After 24 weeks, sessions occurred every 4 weeks, and dietitians called the participants between meetings. Blinded personnel weighed the participants at each meeting and measured their waist circumference every 12 weeks. After 48 weeks, 83% of the choice group and 86% of the comparison group completed all measurements.
The group assigned a diet lost an average 1.1 kg more (95% confidence interval [CI], −2.9 to 0.8 kg; P= .26) than those who chose their diet. Average weight loss in the choice group was 5.7 kg (95% CI, 4.3 – 7.0 kg) compared with an average 6.7 kg (95% CI, 5.4 – 8.0 kg) in the comparison group. Participants in both groups adhered to their diets at similar rates and reported similar measures of physical activity and weight-related quality of life.
Dr Yancy and colleagues offered two possible reasons for the findings: an inclination to overeat when following a diet of more palatable foods and the “personal trainer” effect, in which participants adhere better to a program if told what to do.
The study was funded by the Department of Veterans Affairs. Dr Yancy and three coauthors report receiving grants and/or personal fees from the Department of Veterans Affairs during the study. In addition, Dr Yancy has previously received personal fees from Nutrisystem, one coauthor receives royalties on a patent on the Impact of Weight on Quality of Life-Lite questionnaire, and another coauthor receives royalties from the Pennington Biomedical Research Center of Louisiana State University for intellectual property.
Ann Intern Med. 2015;162:805-814. Abstract

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