Mediterranean-style diet shows modest weight loss and improved diet quality in two-year trial

The DELISH randomized clinical trial enrolled 360 primary care patients with obesity and compared a culturally adapted Mediterranean-style diet program to a commercial weight-loss control intervention over 24 months. Both groups achieved modest, sustained weight loss—approximately 5 kilograms in the Mediterranean group and 4 kilograms in the control group—with no significant difference between them. However, the Mediterranean-style group reported significantly greater improvements in diet quality at all follow-up visits, with higher proportions of energy from healthy fats and lower carbohydrate intake. The findings, published in JAMA Network Open by University of North Carolina researchers, suggest behavioral diet programs can deliver valuable health benefits beyond weight loss alone for the 1 billion adults worldwide living with obesity.

DELISH trial methodology

• ▪The COVID-19 pandemic altered the DELISH trial's intervention delivery and may have affected participation and follow-up.
• ▪The DELISH randomized clinical trial enrolled 360 primary care patients with obesity.
• ▪The DELISH trial collected data on body weight, diet quality, and other physiological parameters at baseline and at 4-month, 12-month, and 24-month follow-up visits.
• ▪Electronic health records provided 24-month weight data for approximately 94% of the DELISH trial sample.
• ▪Approximately 69% of DELISH trial participants attended the final measurement visit.
• ▪Both interventions in the DELISH trial were delivered over a 24-month period.
• ▪The DELISH trial's Mediterranean-style intervention had three phases: phase 1 (1-4 months) focused on improving diet quality, phase 2 (5-12 months) focused on weight loss, and phase 3 (13-24 months) focused on weight loss maintenance.

Mediterranean diet adaptation

• ▪People from different regional, cultural, and ethnic backgrounds may face challenges in applying Mediterranean-specific recommendations to their own lifestyles because the dietary pattern is based on traditional foods from countries around the Mediterranean Sea.
• ▪The Mediterranean dietary pattern prioritizes high-quality fats, such as nuts, seeds, and vegetable oils, and carbohydrates, such as whole grains, fruits, and vegetables.
• ▪Researchers from the University of North Carolina at Chapel Hill developed a Mediterranean-style dietary intervention tailored for populations in the southeastern United States.

Diet quality improvements

• ▪Participants in the DELISH trial's Mediterranean-style group reported greater improvements in diet quality than control participants at all follow-up visits.
• ▪Diet-quality scores improved more in the DELISH trial's Mediterranean-style group than in the control group.
• ▪Diets rich in high-quality carbohydrates and fats are associated with lower risks of cardiovascular disease and several other chronic diseases.
• ▪Among returning participants in the DELISH trial's Mediterranean-style group, the improved dietary pattern was maintained through the 24-month follow-up.
• ▪The DELISH trial's Mediterranean-style group showed a greater proportion of energy from monounsaturated and polyunsaturated fats and a lower proportion of energy from carbohydrates compared to the control group.

Weight loss maintenance

• ▪Blood pressure reductions in the DELISH trial were similar between the Mediterranean-style group and the control group.
• ▪The DELISH trial found no significant difference in the percentage change in body weight between the Mediterranean-style group and the control group at the 24-month follow-up.
• ▪The average reduction in body weight at the 24-month follow-up was approximately 5 kilograms in the DELISH trial's Mediterranean-style group and 4 kilograms in the control group.
• ▪Participants in the DELISH trial's Mediterranean-style intervention group who returned for follow-up achieved about 5 kilograms of weight loss at the 12-month follow-up, which was sustained through the 24-month follow-up.
• ▪Changes in HbA1c in the DELISH trial were minimal overall.
• ▪Changes in physical activity and depression scores in the DELISH trial did not significantly differ between the Mediterranean-style group and the control group.
• ▪Returning participants in the DELISH trial's control group achieved about 4.5 kilograms of weight loss at the 12-month follow-up, which was largely maintained at the 24-month follow-up.

Obesity health risks

• ▪More than 1 billion individuals worldwide are living with obesity, representing 1 in 8 adults.
• ▪Mediterranean-style diets have been shown in randomized trials to reduce cardiovascular events compared with low-fat diets.
• ▪Poor lifestyle behaviors, such as an unhealthy diet and physical inactivity, are major determinants of obesity development and progression.
• ▪Obesity is a well-known risk factor for several chronic diseases, including cardiovascular disease and type 2 diabetes.

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