A two-year primary care trial tested whether putting food quality at the center of weight management could change what participants ate and how well they maintained weight loss.
Paper: Weight Loss Intervention Promoting an Adapted Mediterranean-Style Dietary Pattern. Image Credit: Gecko Studio / Shutterstock
The DELISH randomized clinical trial found that an adapted Mediterranean-style dietary intervention produced modest weight loss comparable to that of a commercial weight-loss program while improving diet quality among adults with obesity. The findings are published in JAMA Network Open.
Background
Obesity, characterized by excessive fat accumulation in the body, has become a major public health challenge worldwide. More than 1 billion individuals worldwide are living with the condition, representing 1 in 8 adults. Obesity is a well-known risk factor for several chronic diseases, including cardiovascular disease and type 2 diabetes.
Poor lifestyle behaviors, such as an unhealthy diet and physical inactivity, are major determinants of obesity development and progression.
A substantial body of evidence suggests that diets rich in high-quality carbohydrates and fats are associated with lower risks of cardiovascular disease and several other chronic diseases, while Mediterranean-style diets have been shown in randomized trials to reduce cardiovascular events compared with low-fat diets.
The Mediterranean dietary pattern, which prioritizes high-quality fats, such as nuts, seeds, and vegetable oils, and carbohydrates, such as whole grains, fruits, and vegetables, has been associated with broad health benefits, although it remains relatively understudied in weight loss intervention trials in the United States.
Since this dietary pattern is based on traditional foods from countries around the Mediterranean Sea, people from different regional, cultural, and ethnic backgrounds may face challenges in applying Mediterranean-specific recommendations to their own lifestyles.
Given these challenges, researchers from the University of North Carolina at Chapel Hill, together with their collaborators, developed a Mediterranean-style dietary intervention tailored for populations in the southeastern United States.
To evaluate the weight-management efficacy of this dietary intervention, they conducted a randomized clinical trial, named Delicious Eating for Life in Southern Homes (DELISH) trial, on 360 primary care patients with obesity.
Trial Design
The participants were randomized to receive either the Mediterranean-style dietary intervention or a control intervention focusing on reducing energy intake. Both interventions were delivered over a 24-month period.
The 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.
The control intervention included access to the workshop and digital components of the WW program (now WeightWatchers), an established commercial weight-loss program. Both groups also received advice to promote regular, moderate-intensity physical activity.
Data on body weight, diet quality, and other physiological parameters were collected at baseline and at 4-month, 12-month, and 24-month follow-up visits.
Key findings
The assessment of participants’ body weight at the 24-month follow-up showed no significant difference in the percentage change in body weight between the Mediterranean-style group and the control group. The average reduction in body weight at the 24-month follow-up was approximately 5 kilograms in the Mediterranean-style group and 4 kilograms in the control group.
Participants in the Mediterranean-style group reported greater improvements in diet quality than control participants at all follow-up visits. The improvement was characterized by a greater proportion of energy from monounsaturated and polyunsaturated fats and a lower proportion of energy from carbohydrates. Diet-quality scores also improved more in the Mediterranean-style group than in the control group.
Significance
This randomized clinical trial found no meaningful difference in weight loss between a Mediterranean-style dietary intervention adapted for the southeastern United States population and an established commercial weight-loss intervention among primary care patients with obesity, most of whom had multiple chronic medical conditions.
However, the Mediterranean-style intervention produced significantly greater improvements in self-reported diet quality than the control intervention, as reflected in diet-quality scores and shifts toward a greater proportion of energy from unsaturated fats and a lower proportion from carbohydrates.
Failure to maintain achieved weight loss is a major disadvantage of intensive weight-loss interventions. In the current trial, among participants who returned for follow-up, those in the Mediterranean-style intervention group achieved about 5 kilograms of weight loss at the 12-month follow-up, which was sustained through the 24-month follow-up.
In the control group, returning participants achieved about 4.5 kilograms of weight loss at the 12-month follow-up, which was largely maintained at the 24-month follow-up. The sustained weight loss in the control group was notable because the researchers had expected greater attenuation after its larger initial weight loss.
Notably, the trial provides detailed insight into intervention-mediated changes in diet quality, which are rarely reported as outcomes in weight-loss trials. Among returning participants in the Mediterranean-style group, the improved dietary pattern was maintained through the 24-month follow-up. If this improved diet quality could be maintained over the long term, the authors note that, based on prior evidence, it would be expected to reduce obesity-related morbidity.
The Mediterranean-style intervention did not, however, show clear superiority across other measured health outcomes. Blood pressure reductions were similar between groups, changes in HbA1c were minimal overall, and changes in physical activity and depression scores did not significantly differ between groups.
Overall, the trial findings suggest that people with obesity who want to avoid or cannot afford weight-loss medications or surgery, or who want to achieve modest weight loss, may consider an intensive behavioral weight-loss intervention as a reasonable option, preferably one that focuses on diet quality.
However, one potential limitation of the trial is its reliance on self-reported diet quality, which may introduce recall and social desirability biases. Furthermore, the Mediterranean-style intervention was adapted for populations in the southeastern United States, which may restrict the generalizability of the findings to other US or international populations.
Only about 69% of participants attended the final measurement visit, although electronic health records provided 24-month weight data for approximately 94% of the sample.
The study also had limited power for subgroup comparisons, and the COVID-19 pandemic altered intervention delivery and may have affected participation and follow-up. In addition, the lack of a usual-care control group means that secular changes affecting body weight could not be fully accounted for.
Facts Only
* A two-year primary care trial tested food quality at the center of weight management to see if it changed eating habits and weight loss maintenance.
* The DELISH randomized clinical trial involved 360 primary care patients with obesity.
* Participants were randomized to receive either a Mediterranean-style dietary intervention or a control intervention focused on reducing energy intake over 24 months.
* The Mediterranean-style intervention had three phases: phase 1 (1-4 months) for diet quality improvement, phase 2 (5-12 months) for weight loss, and phase 3 (13-24 months) for weight loss maintenance.
* The control intervention included access to the WW program and advice on physical activity.
* Body weight was assessed at baseline, 4 months, 12 months, and 24 months.
* The Mediterranean-style group lost approximately 5 kilograms of body weight at 24 months; the control group lost approximately 4 kilograms.
* Participants in the Mediterranean-style group reported greater improvements in diet quality than the control group at all follow-up visits.
* Improvements in diet quality involved a greater proportion of energy from monounsaturated and polyunsaturated fats and a lower proportion from carbohydrates for the intervention group.
* Blood pressure reductions were similar between groups, and changes in HbA1c were minimal overall.
* The Mediterranean-style dietary pattern was adapted for populations in the southeastern United States.
Executive Summary
A two-year randomized clinical trial, the DELISH study, investigated whether centering food quality in weight management could alter dietary intake and weight loss outcomes among adults with obesity. The intervention involved a Mediterranean-style dietary pattern versus a control group receiving an established commercial weight-loss program (WW) and physical activity advice. Both groups followed a three-phase approach: improving diet quality over four months, achieving weight loss over eight months, and maintaining that loss over the final twelve months.
The results indicated that while no significant difference in total weight loss was observed between the two groups at the 24-month mark—the Mediterranean-style group lost approximately 5 kilograms compared to 4 kilograms for the control group—the dietary intervention proved highly effective. Participants in the Mediterranean-style group reported significantly greater improvements in diet quality, characterized by shifts toward higher intake of monounsaturated and polyunsaturated fats and lower carbohydrate consumption. Furthermore, the improved dietary pattern was maintained by participants over the full two years.
Despite the absence of superior weight loss compared to the control group, the intervention demonstrated substantial benefits in nutritional quality. The trial also showed that weight loss was sustained in both groups; the sustained weight loss in the Mediterranean-style group was comparable to the larger initial losses seen in the control group. Other health markers, such as blood pressure and HbA1c changes, did not significantly differ between the intervention arms. The study is limited by reliance on self-reported data and adaptation for a specific US population.
Full Take
The study reveals a tension between the pursuit of quantifiable outcomes (weight loss) and the achievement of qualitative health improvements (diet quality). The finding that the Mediterranean approach did not yield greater weight loss than an established commercial program, despite fostering superior dietary patterns, challenges the conventional assumption that optimizing diet inherently leads to differential caloric deficits in this context. This suggests that the mechanism by which weight is lost might be more influenced by energy restriction alone, rather than the specific quality of the food consumed within a general pattern framework.
The most significant implication lies in the dissociation between outcome measures: successful attainment of weight loss versus superior dietary adherence. The fact that participants in the Mediterranean group maintained their improved diet quality over two years, and this quality correlated with lower obesity-related morbidity risk (as suggested by prior evidence), points toward a potential bottleneck in weight management interventions—the maintenance of behavior change rather than the initial shift in mass. The limitation concerning self-reported data highlights a crucial systemic challenge: if interventions are designed to foster long-term habit shifts, relying solely on retrospective self-reporting risks obscuring true behavioral efficacy, especially when compared against established markers like blood pressure or glucose control which showed no divergence between groups.
When considering generalization, the adaptation of the pattern for the southeastern US introduces a critical boundary condition. This forces an examination of whether generalizable nutritional principles can be effectively translated across diverse cultural and environmental contexts without losing their power. The unanswered question is whether interventions focusing on *quality* as a primary metric can establish themselves as equally valid predictors of long-term health, or if they must ultimately interface with energy balance metrics to produce clinically meaningful results.
Bridge Questions: If the trial design had separated weight loss from diet quality as primary endpoints, would the intervention show superiority? What specific psychological or cultural factors mediate the maintenance of dietary quality across different populations? How can research effectively integrate subjective experience (diet quality) with objective physiological measures to define true success in obesity treatment?
Sentinel — Human
The text reads like a standard, well-structured summary of a clinical trial, effectively balancing statistical results with necessary contextual limitations and caveats.