NORTH CAROLINA — The Mediterranean-style diet group lost an average of 3.4% of their body weight at the 24-month mark, while the control group with access to WeightWatchers lost an average of 3.51%. The difference in weight loss between the two groups was not statistically significant, with a P-value of 0.90. Both groups fell below the 5% weight loss threshold generally considered clinically meaningful.

Participants in the study had a mean age of 54.7 years, and 55.6% were women. At baseline, the median weight of participants was 227.5 lbs, with a median body mass index (BMI) of 35.1. Most participants entered the trial with multiple chronic medical conditions. The adjusted mean weight loss for the Mediterranean-style diet group was 8.7 lbs, compared to 8.8 lbs for the control group.

The Mediterranean-style diet group showed improved diet quality. The Alternative Healthy Eating Index-2010 score was higher in the Mediterranean-style diet group than in the control group, with a difference of 3.62 points. Participants in the Mediterranean group consumed more total, polyunsaturated, and monounsaturated fat, and fewer carbohydrates as a percentage of total energy intake.

The Mediterranean-style weight-loss program, known as Med-South, was tailored for the Southeastern U.S. and incorporated regional foods such as black-eyed peas, collard greens, and sweet potatoes. Registered dietitians delivered the program in three phases: Phase 1 (months 1-4) focused on diet quality, Phase 2 (months 5-12) on weight loss, and Phase 3 (months 13-24) on weight maintenance. Physical activity and depression scores did not differ significantly between the groups during the trial.

Thomas Keyserling, MD, MPH, of the UNC Center for Health Promotion and Disease Prevention in Chapel Hill, North Carolina, reported the findings. "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, Keyserling said."

Keyserling added that other options may be more effective for substantial weight reduction. For individuals who wish to lose substantial weight (>10% of body weight), GLP-1 agonist treatment or bariatric surgery are good choices," he said."

Participant satisfaction remained high in the Mediterranean group despite the weight loss results. At 24 months, 94.8% of Mediterranean-style diet participants said they would recommend their assigned program, compared to 68.3% of WeightWatchers participants. The trial’s primary outcome was measured using calibrated scales tested monthly for accuracy up to 350 pounds.

There were 41 serious adverse events reported across both groups, with no significant difference in frequency. One control participant using hypertension medication experienced near syncope after substantial weight loss.

Why It Matters

North Carolina has one of the highest rates of obesity in the United States, with a prevalence of 36.2% among adults as of 2024, according to the Centers for Disease Control and Prevention (CDC). The DELISH trial provides data on behavioral interventions in a region with high obesity rates, though regional tailoring to the Southeastern U.S. may limit the generalizability of the findings to other populations. Study limitations included self-reported diet quality and an inability to control for non-study drugs associated with modest weight loss, such as SGLT2 inhibitors.

Keyserling suggested that maintaining improved diet quality could have long-term health benefits. "if the improved diet quality observed among Mediterranean-style intervention participants could be maintained over time, it would be expected to reduce obesity-related morbidity," he said.

What's New

In the DELISH trial, 41 serious adverse events were reported across both groups, with no significant difference in frequency between the Mediterranean-style diet group and the WeightWatchers-based control group. The Alternative Healthy Eating Index (AHEI)-2010, used to measure diet quality in the DELISH trial, showed a mean score increase of 3.62 points in the Mediterranean-style group compared to the control group, which is equivalent to an improvement in dietary quality that could reduce chronic disease risk by up to 12% over time. In the 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.

In the DELISH trial, 94.8% of participants in the Mediterranean-style group reported they would recommend their program, indicating high participant satisfaction despite no significant weight loss advantage over the control group. The DELISH trial’s primary outcome, weight loss at 24 months, was measured using calibrated scales tested monthly for accuracy up to 350 pounds, ensuring reliable data collection across both groups. The Med-South program, tailored for the Southeastern U.S. incorporated regional foods such as black-eyed peas, collard greens, and sweet potatoes, which are commonly consumed in North Carolina and other Southern states.

How Sources Differ

Sources differ on the reporting of adverse events and weight loss metrics. Desk_web stated that in the 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.

JAMA Network Open DELISH trial publication stated that the Alternative Healthy Eating Index-2010 score was significantly higher in the Mediterranean-style diet group than in the control group in the DELISH trial (difference 3.62, 95% CI 1.11-6.12, P=0.005).

JAMA Network Open DELISH trial publication stated that the Mediterranean-style diet group in the DELISH trial lost an average of 3.4% of their body weight at 24 months.

JAMA Network Open DELISH trial publication stated that the control group in the DELISH trial, which had access to WeightWatchers, lost an average of 3.51% of their body weight at 24 months.

JAMA Network Open DELISH trial publication stated that the difference in weight loss between the Mediterranean-style diet group and the control group in the DELISH trial was not statistically significant (P=0.90).

JAMA Network Open DELISH trial publication stated that the adjusted mean weight loss for the Mediterranean-style diet group in the DELISH trial was 8.7 lbs at 24 months.

JAMA Network Open DELISH trial publication stated that the Mediterranean-style weight-loss program in the DELISH trial was delivered by registered dietitians in three phases: Phase 1 (months 1-4) for diet quality, Phase 2 (months 5-12) for weight loss, and Phase 3 (months 13-24) for weight maintenance.

JAMA Network Open DELISH trial publication stated that at 24 months, 94.8% of Mediterranean-style diet participants in the DELISH trial said they would recommend their assigned program.