A Randomized Clinical Trial Testing Treatment Preference and Two Dietary Options in Behavioral Weight Management: Preliminary Results of the Impact of Diet at 6 Months—PREFER Study

Objective: The PREFER study objectives were to examine potential differences in weight loss during a standard behavioral intervention between subjects assigned to one of two calorie‐ and fat‐restricted diets [standard behavior treatment (SBT) and lacto‐ovo‐vegetarian ([SBT+LOV)], with or without regard to their preferred dietary treatment. This article reports the differences in outcomes between diet groups after the first 6 months of the intervention. Research Methods and Procedures: The study used a four‐group design. Subjects ( n = 182) were randomized to a treatment preference group and then to a dietary treatment group. For this report, preference groups were combined to permit comparisons by dietary treatment only (SBT, n = 98; SBT+LOV, n = 84). Additional analyses compared SBT+LOV subjects who were 100% adherent (did not consume any meat, fish, or poultry, n = 47) to those who were <100% adherent ( n = 24). Results: Significant differences were seen in the baseline to 6‐month change scores between the two groups for carbohydrate consumption ( p = 0.013), protein consumption ( p < 0.001), polyunsaturated‐to‐saturated fat ratio ( p = 0.009), and low‐density lipoprotein‐cholesterol (LDL‐C) level ( p = 0.013). Among SBT+LOV subjects, those who were 100% adherent experienced greater reductions in weight ( p < 0.001), total cholesterol ( p = 0.026), LDL‐C ( p = 0.034), and glucose ( p = 0.002) and consumed less fat ( p = 0.030) compared with those who were <100% adherent. Discussion: Differences between dietary treatment groups at 6 months were minimal, most likely because one‐third of the SBT+LOV group did not follow the vegetarian diet and because both groups had the same calorie and fat restrictions. SBT+LOV subjects who were 100% adherent were more successful at both weight loss and cholesterol reduction than those who were <100% adherent, suggesting that vegetarian diets are efficacious for weight and cholesterol control.