Popular Diet May Not Help for Weight, but Trial Points to Another Benefit

A Mediterranean-style diet program did not lead to greater weight loss compared with a control intervention among primary care patients with obesity, though it did improve diet quality, the DELISH trial showed.

Missing the trial’s primary endpoint, the Mediterranean-style diet group lost an average 3.4% of their body weight at 24 months compared with an average loss of 3.51% in a control group that had access to WeightWatchers (P=0.90), reported Thomas Keyserling, MD, MPH, of the UNC Center for Health Promotion and Disease Prevention in Chapel Hill, North Carolina, and colleagues.

This translated to an adjusted mean weight loss of 8.7 lbs and 8.8 lbs, respectively, though both groups fell below the 5% threshold considered clinically significant.

While there was no difference in weight loss, the Alternative Healthy Eating Index-2010 score was significantly higher in the Mediterranean-style diet group versus the control group (difference 3.62, 95% CI 1.11-6.12, P=0.005), meeting the trial’s secondary endpoint.

The findings “provide insights for evolving weight loss paradigms,” given the popularity of highly effective GLP-1 drugs and bariatric surgery, the authors wrote in JAMA Network Open.

“For individuals who wish to lose substantial weight (>10% of body weight), GLP-1 agonist treatment or bariatric surgery are good choices,” Keyserling and team advised. “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.”

Of note, “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,” they pointed out.

Hallmarks of a “healthful dietary pattern” include regular consumption of high-quality fats — vegetable oils, nuts, seeds, and fish — plus carbohydrates like whole grains, fruits, and non-starchy vegetables, alongside a reduced intake of refined carbohydrates and processed foods.

Emily Case, a registered dietitian at Northwell Health in New York, who was not involved with the study, said the Mediterranean diet “provides a clear blueprint for food choices that are healthy and nutritious,” and has been regularly recognized as a top diet.

“A person could technically count calories but still choose highly processed, nutrient-poor foods, like low-calorie crackers or diet soda,” she said in a statement. “The Mediterranean diet participants … [ate] more fruits, vegetables, legumes, seeds, nuts, and less refined carbs.”

Case said that if weight loss is the goal, overeating healthy food is still possible. “I would still coach a patient on what the appropriate portion sizes are,” she noted. “I have seen patients who, because they have shifted to more quality, feel strongly that they can eat more, and then they don’t lose weight.”

The DELISH trial randomized 360 patients from one academic and six community primary care practices in central North Carolina. Mean age was 54.7, and 55.6% were women. At baseline, median weight and body mass index (BMI) were 227.5 lbs and 35.1, respectively, and most participants had multiple chronic medical conditions.

The Mediterranean-style weight-loss program was delivered by registered dietitians in three phases:

• Phase 1 (months 1-4): diet quality phase
• Phase 2 (months 5-12): weight loss phase
• Phase 3 (months 13-24): weight maintenance phase

As a percentage of total energy intake, the Mediterranean-style diet participants consumed more total, polyunsaturated, and monounsaturated fat, and fewer carbs. Physical activity and depression scores did not differ significantly between groups.

There was nominally greater weight loss for other races besides Black and white, men, and those with diabetes, older age, and higher BMI, though no subgroup interactions were significant. One control participant using hypertension medication experienced near syncope after substantial weight loss.

At 24 months, 94.8% of Mediterranean-style diet participants and 68.3% of WeightWatchers participants said they would recommend their assigned program.

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, the authors acknowledged. Regional tailoring to the Southeastern U.S. may also limit generalizability.

Future research should clarify how heavily diet quality affects long-term health outcomes in weight-loss interventions, the team noted.

“In the meantime, given the robust association between a healthful dietary pattern and improved health outcomes, consideration should be given to prioritizing a healthful dietary pattern as a key component of behavioral weight loss interventions,” they concluded.