Weight Loss Intervention Promoting an Adapted Mediterranean-Style Dietary Pattern: The DELISH Randomized Clinical Trial.

Importance: A Mediterranean-style dietary pattern has been shown to reduce chronic disease morbidity yet has been understudied in weight loss intervention trials in the US. Weight loss interventions promoting this pattern may reduce obesity-related morbidity more than interventions primarily focusing on energy restriction. Objective: To determine whether a behavioral weight loss intervention promoting a Mediterranean-style dietary pattern yields sustained weight loss at the 24-month follow-up and improves diet quality compared with a control intervention focused on reducing energy intake. Design, Setting, and Participants: This randomized clinical trial (Delicious Eating for Life in Southern Homes [DELISH]) recruited patients from 1 academic and 6 community primary care practices in central North Carolina. Electronic health records at these facilities were used to identify potential participants who met the major inclusion criteria of a body mass index of 30 or higher (calculated as weight in kilograms divided by height in meters squared) and age of 18 to 75 years. Primary care practitioners reviewed a list of their identified patients and referred those whom they considered appropriate for the trial. Enrollment spanned June 12, 2020, to May 11, 2022, with final data collected on June 16, 2024. Statistical analyses were conducted from June 6, 2024, to July 19, 2026, using an intention-to-treat approach. Interventions: Participants were randomly assigned to receive 1 of 2 interventions-Med-South weight loss program (hereafter Mediterranean-style) or control weight loss program. The Mediterranean-style intervention included 3 phases: phase 1 (months 1-4) focused on improving diet quality, phase 2 (months 5-12) focused on weight loss, and phase 3 (months 13-24) focused on weight loss maintenance. The control intervention included access to the workshop and digital components of the WW program (now WeightWatchers). Participants in each group received the study intervention at no cost, and the interventions provided advice to promote regular, moderate-intensity physical activity. Main Outcomes and Measures: The primary outcome was percentage change in body weight between intervention groups at the 24-month follow-up. Secondary outcomes included changes in diet quality, physiological functions, and physical activity, among others. Results: A total of 360 participants (182 in the Mediterranean-style group; 178 in the control group) were included, with a baseline mean (SD) age of 54.7 (12.0) years and 200 females (55.6%). The median (IQR) weight and body mass index were 103.2 (93.2-118.8) kg and 35.1 (32.4-40.2), respectively. Follow-up at 24 months was attended by 118 patients (64.8%) in the Mediterranean-style group and 129 (72.5%) in the control group. In the primary analysis with imputation for missing data, the adjusted mean (SE) percentage change in body weight at the 24-month follow-up was -3.40% (0.60%) for Mediterranean-style intervention and -3.51% (0.66%) for the control intervention (difference, -0.11; 95% CI, -1.79 to 1.57; P = .90). Among participants who returned for follow-up visits, the Alternative Healthy Eating Index-2010 score was higher among the Mediterranean-style group compared with the control group (difference, 3.62; 95% CI, 1.11-6.12; P = .005). Conclusions and Relevance: In this randomized clinical trial comparing a Mediterranean-style weight loss intervention to a control intervention, there was no material difference in percentage change in body weight at the 24-month follow-up visit between participants in these programs. Trial Registration: ClinicalTrials.gov Identifier: NCT04302727.