TOPLINE

A 24‑month behavioral weight-loss program promoting a Mediterranean‑style diet did not produce greater weight loss than a calorie-restricting commercial weight-loss program, with participants in both groups losing roughly 3.5% of body weight. However, participants in the Mediterranean-style group reported significantly greater improvements in diet quality.

METHODOLOGY

• Mediterranean-style dietary patterns have been shown to reduce the risk for chronic diseases but have been relatively understudied in US behavioral weight-loss trials, which typically emphasize calorie restriction or low-fat strategies rather than diet quality.
• Researchers conducted a randomized trial among 360 participants with obesity from primary care practices in North Carolina (mean age, 54.7 years; 55.6% women; median BMI, 35.1) and assigned them to a Mediterranean-style weight-loss program or a control weight-loss program over 24 months.
• The Mediterranean-style program, delivered by registered dietitians, had three phases, with phase 1 (months 1-4) focused on boosting diet quality but not weight loss, phase 2 (months 5-12) focused on weight loss, and phase 3 (months 13-24) focused on weight-loss maintenance. The control intervention provided access to the workshop and digital components of a commercial weight-loss program for 2 years. Both groups received guidance to encourage regular moderate-intensity physical activity.
• Data were collected before baseline and over 24 months via online surveys about diet and lifestyle, in-person health checkups, counseling visits, and access to data on program usage logs.
• The primary outcome was percentage change in body weight at 24 months. Change in diet quality — measured using validated indexes derived from food frequency questionnaires, with higher scores reflecting better diet quality — was one of the secondary outcomes of this trial.

TAKEAWAY

• At 24 months, the adjusted mean percentage change in body weight was -3.40% for the Mediterranean-style group and -3.51% for the control group (difference, -0.11%; P = .90), indicating no statistically significant difference.
• Diet quality improved significantly more in the Mediterranean-style group than in the control group as early as 4 months, with the gap remaining statistically significant through 24 months across multiple measures of eating habits, though it narrowed somewhat from its peak at 12 months (P < .05 for all).
• At 24 months, the Mediterranean-style group obtained a greater share of energy from total fat, monounsaturated fat, and polyunsaturated fat and a slightly lower share of energy from carbohydrates (P < .05 for all).
• Systolic and diastolic blood pressure declined similarly in both groups. A1c changes were small in both groups overall, but at 24 months, the control group had a significantly greater reduction than the Mediterranean-style group (difference, -0.22 percentage points; 95% CI, -0.41 to -0.03).

IN PRACTICE

“For individuals who want to avoid or cannot afford weight‑loss medications or surgery or whose goal is to achieve modest weight loss (< 10% of body weight), an intensive behavioral weight‑loss intervention is a reasonable choice, preferably one that emphasizes diet quality,” the authors of the study wrote.

SOURCE

The study was led by Thomas C. Keyserling, MD, MPH, University of North Carolina at Chapel Hill. It was published online on August 20, 2026, in JAMA Network Open.

LIMITATIONS

Diet quality was self-reported, so recall and social desirability bias may have influenced the results. The trial had limited statistical power for subgroup comparisons of weight change and did not include a usual‑care control group. Finally, because the Mediterranean-style program was tailored to the Southeastern US population, the findings may not generalize to other regions.

DISCLOSURES

The trial was funded by the National Heart, Lung, and Blood Institute. Several authors reported grants from the study funder and disclosed industry ties, including salary support, personal fees or consulting, and stock or stock options with various pharmaceutical and biotech companies.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.