In a two-year head-to-head trial, researchers found that two very different dietary approaches produced similar changes in body weight.
A Mediterranean-style eating plan adapted to Southern food preferences helped participants lose about as much weight as WeightWatchers over two years, but it produced substantially greater improvements in reported diet quality. The comparison was part of the DELISH (Delicious Eating for Life in Southern Homes) study, which examined whether a culturally tailored Mediterranean-style diet could support weight loss while addressing cardiovascular disease (CVD) risk.
Researchers from UNC-Chapel Hill worked with collaborators at East Carolina, Duke, Harvard, and Simmons Universities. Their findings were recently published in JAMA Network Open. The research was led by co-Principal Investigators Thomas Keyserling, MD, MPH, professor at the UNC School of Medicine, and Carmen Samuel-Hodge, PhD, RD, professor of nutrition at UNC Gillings School of Global Public Health. Both are research fellows at the UNC Center for Health Promotion and Disease Prevention, which served as the administrative home for the study.
A Mediterranean diet adapted for the Southeast
Communities in the Southeastern United States experience a greater burden from chronic diseases including diabetes, CVD, and stroke. Dietary patterns are among the lifestyle factors that can influence the development and progression of these conditions.
Previous research has found that diets emphasizing high-quality fats (nuts, seeds, vegetable oils) and carbohydrates (whole grains, fruits, vegetables) can reduce CVD risk more effectively than conventional low-fat weight loss diets. Mediterranean-style diets follow these principles while limiting refined carbohydrates and processed foods.
But recommendations rooted in Mediterranean cuisine may not fit equally well with the foods, preferences, and traditions of every regional, cultural, or ethnic community. To address that gap, the researchers developed the Med-South Weight Loss Program (Med-South), which follows a Mediterranean-style dietary pattern while adapting its recommendations to Southeastern food availability and taste preferences.
Two weight loss programs tested head to head
The researchers wanted to determine whether Med-South could produce sustained weight loss after 24 months while improving diet quality compared with a control program focused primarily on reducing calorie intake.
The study included 360 adults with a body mass index of ≥ 30 who were recruited from primary care practices in central North Carolina. Participants were randomly assigned to one of two interventions: the Med-South Weight Loss Program (Med-South) or a control weight loss program, WeightWatchers (previously called WW).
Med-South participants moved through three phases during the 24-month study. The first focused on improving diet quality, the second emphasized weight loss while maintaining the Med-South eating pattern, and the third focused on maintaining the weight that had been lost. Participants in the control group received access to WW workshops and digital resources throughout the two years.
Researchers measured body weight, diet quality, blood pressure, and other outcomes at 4, 12, and 24 months. Diet quality was assessed using food intake questionnaires and the Veggie Meter, a device that measures carotenoid levels in the skin. Carotenoids are compounds found in many fruits and vegetables, and skin carotenoid measurements have been shown to correlate with fruit and vegetable consumption.
Diet quality improved without greater weight loss
After 24 months, participants in both groups had lost weight and maintained that loss. Among those who returned for follow-up, the average reduction was about 4.5 kg, or roughly 10 pounds.
The researchers found no significant difference between Med-South and WeightWatchers in either weight loss or the observed decrease in blood pressure. The groups differed more clearly in diet quality.
Med-South participants reported substantially better dietary patterns, including greater consumption of high-quality fats (poly and monounsaturated fats), lower carbohydrate intake, and substantially higher scores on measures of overall diet quality. Veggie Meter scores improved in both groups.
Given the findings of this study, Keyserling notes that, “Incorporating a healthful dietary pattern into lifestyle weight loss programs should be a priority. While similar weight loss can be achieved with calorie-restricted diets, there are added benefits to chronic disease prevention associated with a healthful dietary pattern.”
Reference: “Weight Loss Intervention Promoting an Adapted Mediterranean-Style Dietary Pattern: The DELISH Randomized Clinical Trial” by Thomas C. Keyserling, Qiang Wu, Alice S. Ammerman, Seth A. Berkowitz, John B. Buse, David J. Couper, Kelly R. Evenson, Steven D. Hursting, Daniela Sotres-Alvarez, Kiira Lyons, Veeral M. Saraiya, Candice L. Alick, Harlyn G. Skinner, Caroline Nelson, Lauren M. Kruse, Alison N. Mathers, Teresa T. Fung, Stephanie B. Jilcott Pitts, Eric Andrew Finkelstein and Carmen D. Samuel-Hodge, 20 August 2026, JAMA Network Open.
DOI: 10.1001/jamanetworkopen.2026.29006
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