Adopting a Mediterranean diet helped older adults shed weight and improve metabolic health, but new research shows it may not be enough to enhance cognitive function, highlighting the need for longer or more intensive interventions.
Study: Long-term outcomes of a Mediterranean diet with or without calorie restriction on cognition and cardiometabolic health: The building research in diet and cognition trial. Image Credit: Liubomyr Tryhubyshyn / Shutterstock
In a recent study published in the journal Preventive Medicine Reports, researchers in Chicago, USA, investigated whether adopting a Mediterranean Diet (Med Diet) lifestyle, with or without calorie-restricted weight loss, improves cognition and cardiometabolic health over a 14-month period.
Background
Could a plate of olive oil-dressed vegetables protect the aging brain as effectively as expensive drugs? Alzheimer’s dementia impacts about 6.9 million Americans older than 65 years, and pharmacologic options offer only modest relief.
Observational data link both a Med Diet pattern and intentional weight reduction to sharper cognition, yet rigorous evidence is scarce for African American adults, who shoulder disproportionate dementia and obesity burdens in the United States (US). Existing randomized trials are often short, enroll predominantly White volunteers, or fail to distinguish between dietary and weight-loss effects.
About the study
The Building Research in Diet and Cognition (BRIDGE) Randomized Controlled Trial (RCT) enrolled 185 community-dwelling adults aged 55-85 years with obesity. Eligibility included Body Mass Index (BMI) 30-50 kg/m2, low Med Diet adherence, Montreal Cognitive Assessment scores ≥19, and 91% identified as African American. Participants were randomized 2:2:1 to the Med Diet with Weight Loss (MedWL), the Med Diet alone (MedA), or the control group. Stratified blocks balanced age, cognition, and cohort; outcome assessors were blinded.
Both intervention groups attended twenty-five weekly classes for eight months, received extra-virgin olive oil and almonds, and learned to cook using the Mediterranean diet. MedWL additionally pursued 5-7% weight loss via a 25% calorie deficit and 150 minutes per week of moderate-to-vigorous physical activity coached by certified trainers.
All participants then completed a six-month low-contact maintenance phase. Cognition, attention, and information processing (AIP), executive function, and learning, memory, and recognition (LMR) were assessed with standard neuropsychological tests. Secondary outcomes encompassed diet quality, body weight, body composition assessed by Dual-energy X-ray Absorptiometry (DXA), Homeostasis Model Assessment of Insulin Resistance (HOMA-IR), High-Sensitivity C-Reactive Protein (hs-CRP), Hemoglobin A1c (HbA1c), and six-minute walk distance. Investigators analyzed intention-to-treat change from baseline to 14 months with linear mixed-effects models that adjusted for cohort, age, and baseline cognitive performance.
It is important to note that, for the third cohort, several physical activity and functional outcome measures, including the six-minute walk test, were affected by the COVID-19 pandemic, as data collection for these outcomes had to be conducted virtually or was omitted due to restrictions.
Study results
Among 185 randomized participants, 162 (88%) contributed outcome data at 14 months. The baseline mean age was 66 years, and the mean BMI was 37.1 kg/m²; 86% of the participants were female.
During the eight-month active phase, adherence to the Med Diet rose markedly in both intervention arms, and weight loss occurred primarily in the MedWL group; these trends largely persisted through the maintenance phase.
Over the full 14 months, adherence scores increased by 3.2 points for MedWL and 3.4 points for MedA, compared to 0.2 points for controls (P < 0.05), indicating sustained dietary change.
MedWL participants recorded an average weight reduction of 3.8 kg, compared with a non-significant 1.7 kg in MedA and 0.5 kg in controls; the difference between MedWL and both comparators was statistically significant.
Visceral adipose tissue mass declined by 151 g in MedWL, representing a significant reduction compared to the control group, but not in the other groups. Additionally, BMI fell by 1.4 kg/m² in MedWL only.
Despite these favorable metabolic shifts, cognitive composites changed similarly across groups.
AIP, Executive Function, and LMR scores each improved modestly within all arms, likely reflecting practice effects; however, no between-group differences emerged from baseline to 14 months or from 8 to 14 months.
Significant between-group differences were also seen in secondary outcomes, including Med Diet adherence, weight, BMI, and visceral adipose tissue mass.
For hs-CRP, the only statistically significant between-group difference was a larger drop in the MedWL group compared to MedA. Changes in other cardiometabolic outcomes such as HOMA-IR, HbA1c, fasting lipids, blood pressure, and six-minute walk distance were modest and did not differ significantly between groups.
Sensitivity analyses excluding measures collected virtually during the Coronavirus Disease 2019 pandemic or omitting tests unavailable to the third cohort yielded similar findings, supporting the accuracy of null cognitive results.
Notably, adherence to the Med Diet waned slightly during maintenance, dropping 2.9 points in MedWL and 1.4 points in MedA; yet, it remained higher than baseline, and weight regain in MedWL was limited to approximately 0.9 kg.
Physical activity, as measured by the Godin questionnaire, increased during classes but remained essentially unchanged from baseline at the end of maintenance in MedWL (change of +0.2). The six-minute walk distance declined in some groups, although for the third cohort, this outcome was omitted due to pandemic-related restrictions.
Systolic and diastolic blood pressure remained unchanged. Insulin and triglyceride values showed wide confidence intervals and no group differences. The paper does not report on adverse events attributable to diet or exercise. These activity trends did not measurably mediate cognitive change.
Conclusions
To summarize, an eight-month Med Diet lifestyle intervention, delivered with or without calorie-restricted weight loss and followed by six months of low-contact maintenance, did not enhance cognition in older African American adults with obesity compared with a usual diet. Nevertheless, participants safely improved dietary quality, and the weight-loss arm achieved clinically meaningful reductions in body weight and visceral adiposity.
These gains underscore the practicality of culturally sensitive group programs for cardiometabolic risk management but suggest that stronger or longer exposures may be required to translate metabolic benefits into cognitive protection. Replication in larger, multi-ethnic cohorts and extended follow-up is warranted. Further research is needed to clarify long-term cognitive influence in diverse communities.