According to a two-year study published in JAMA Network Open, a Mediterranean-style diet adapted for the Southern U.S. and a calorie-focused weight loss program resulted in similar average weight loss of about 3.4% and 3.5% respectively, though the Mediterranean group achieved significantly higher overall diet quality.
Study Design and Participant Demographics
The research tracked 360 individuals recruited from North Carolina primary care practices. Participants carried a body mass index (BMI) of 30 or greater and logged an average age of 55. Most individuals also managed multiple chronic conditions, including hypertension and diabetes. Researchers randomly divided the cohort into two arms: 182 participants entered the Mediterranean-style diet group, while 178 joined a control weight-loss program.
The intervention lasted 24 months, with formal assessments scheduled at 4, 12, and 24 months. The Mediterranean-style diet program—locally termed Med-South—unfolded across three distinct phases. Phase 1 spanned months one through four and prioritized diet quality improvements. Phase 2 covered months five through 12 and shifted focus to weight loss. Phase 3 encompassed months 13 through 24 and targeted weight loss maintenance. Registered dietitians led the program, steering participants toward whole grains, healthy fats, fruits, and vegetables while actively discouraging refined carbohydrates and processed foods.
Comparing Program Structures and Outcomes
The control group gained access to workshop resources and digital components through the WeightWatchers program, which centers primarily on calorie reduction while encouraging produce intake. By the conclusion of the 24-month trial, both groups achieved nearly identical average weight loss. The Mediterranean-style group lost 3.4% of their body weight, compared with 3.5% in the control group. Furthermore, clinical assessments revealed no statistically significant differences between the two cohorts in secondary outcomes like blood pressure changes.
Pro Tip: When evaluating commercial weight management tools, consider how structured point allocations or lifestyle apps like WW (formerly Weight Watchers) and Noom handle daily tracking, coaching access, and consistency features to support long-term behavioral changes.
Expert Perspectives on Diet Quality Versus Calories
Christopher Gardner, a professor of medicine at the Stanford Prevention Research Center who did not participate in the study, noted that diet quality served as a secondary outcome rather than the primary endpoint. Gardner explained that while calorie restriction drives weight reduction over time, selecting higher-quality foods supplies necessary vitamins and minerals that support metabolic health over the long term.
“Weight loss is typically achieved by a prolonged period of calorie restriction. It is possible to eat nothing but junk food and lose weight if the amount of total food consumed does not meet the caloric needs of the person,” Gardner stated.
Supporting that view, Kristin Kirkpatrick, president of KAK Consulting and a dietitian at the Cleveland Clinic Department of Wellness & Preventive Medicine, emphasized that prioritizing quality over quantity safeguards against nutrient depletion. “This study follows the same insight that a high quality diet can beneficially impact not only weight loss success but overall health outcomes as well,” Kirkpatrick noted.
Long-Term Adherence and Health Implications
Beyond scale weight, the trial uncovered major differences in how participants viewed their respective programs. A striking 95% of individuals in the Mediterranean-style group reported they would recommend the program to others, compared with 68% of participants in the control group. The Mediterranean group also increased their intake of whole grains, vegetable oils, nuts, fruit, and non-starchy vegetables.
These findings align with data from the 2024 DIETFITS trial, which demonstrated that high dietary adherence combined with elevated diet quality produces the strongest weight loss results. Researchers emphasize that while calorie balance remains essential for dropping pounds, choosing nutrient-dense options makes managing those calories easier and protects against chronic conditions like cardiovascular disease, stroke, dementia, and diabetes.
Did you know? Incorporating nutrient-dense ingredients like leafy greens and berries into daily meals—whether through whole foods or high-fiber smoothies—can enhance satiety and help individuals stick to their target calorie goals without feeling deprived.
Frequently Asked Questions
Did the Mediterranean diet cause more weight loss than the calorie-focused program?
No. Both groups achieved nearly identical average weight loss over the two-year period, with the Mediterranean group losing 3.4% and the control group losing 3.5%.
Why is diet quality considered important if weight loss was similar?
According to experts like Kristin Kirkpatrick and Christopher Gardner, a high-quality diet protects against chronic disease risks and provides essential vitamins and minerals necessary for a healthy metabolism.
Do calories still matter if you eat a Mediterranean-style diet?
Yes. Experts point out that energy balance through calorie restriction is still required for weight loss, though higher-quality foods can make managing those calories easier.
What is your approach to balancing calorie restriction with diet quality? Share your thoughts in the comments below, explore our related nutrition guides, or subscribe to our newsletter for weekly health updates.
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