Study shows no significant cognitive benefit of adhering to Mediterranean diets regardless of calorie intake

By Pooja Toshniwal PahariaReviewed by Lily Ramsey, LLMApr 24 2023

In a recent study published in Preventive Medicine Reports Journal, researchers performed a randomized clinical trial (RCT) to investigate whether adhering to the Mediterranean diet (MedDiet) with or without limiting calorie intake could improve cognition.

Study: Effect of Mediterranean diet and Mediterranean diet plus calorie restriction on cognition, lifestyle, and cardiometabolic health: A randomized clinical trial. Image Credit: ElenaEryomenko/Shutterstock.com

Background

Obesity, lifestyle choices including diet and exercise, and cardiometabolic comorbidities elevate the risk of cognitive decline. To date, there are no efficient pharmaceutical therapeutics available to prevent, retard, or manage cognitive deficits.

However, studies have shown that MedDiet and weight loss benefit cognition, and combining the two may enhance cognitive function. However, RCTs have shown inconsistent results, with either a favorable or negligible impact of nutrition on cognition, warranting further research.

About the study

In the present three-arm RCT, researchers evaluated the potential cognitive benefit of adhering to MedDiet with or without limiting calorie intake.

The Building Research in Diet and Cognition study was conducted between January 2017 and October 2020, involving 185 residents of Chicago, aged 55 to 85 years, largely female sex (86.0%), with obesity. The participants were randomly allocated to the MedDiet with calorie limitation (n=72, 25.0% kcal restriction for 5.0 to 7.0% loss of weight) intervention group, MedDiet alone group (n=72), or control group (n=36).

The period of the dietary interventions was eight months, including 26 sessions for the intervention groups and 25 sessions for the control group, and follow-up assessments were performed over 14.0 months.

The primary study outcome was a change in the cognitive assessment scores for attention, information, and processing (AIP); learning, memory, and recognition (LMR); and executive function (EF).

Secondary study outcomes were changes in body weight, cardiometabolic biomarkers, and lifestyle. The team estimated habitual dietary consumption using the Harvard food frequency questionnaires (HFFQS), and physical activity was estimated using a triaxial accelerometer worn on the non-dominant wrist for ≥4.0 days and ≥10.0 hours daily.

To assess cardiometabolic risk, blood pressure, serological levels of low-density lipoprotein-cholesterol (LDL-C), high-density lipoprotein-cholesterol (HDL-C), total cholesterol, triglycerides (TGs), insulin, glycated hemoglobin (HbA1c), high sensitivity C-reactive protein (hs-CRP), and glucose levels were measured in blood samples provided by the patients.

Individuals were recruited via presentations in senior facilities and advertisements in local neighborhoods, and they underwent telephonic and physical screening before enrollment.

Individuals with body mass index (BMI) ranging from 30.0 to 50.0 kg/m², Mediterranean diet adherence screener score ≤6.0, Montreal Cognitive Assessment (MoCA) scores ≥19.0, and those who could speak in English were included in the analysis.

The team excluded individuals who could not exercise according to the EASY physical activity screener, serological HbA1c values >9.0 at screening, and significant comorbidities such as autoimmune disorders or severe cardiovascular, pulmonary, renal, and hepatic diseases.

In addition, individuals using warfarin, suffering from severe psychiatric conditions, individuals with a history of bariatric surgery, individuals concurrently involved in formal bodyweight reduction programs, and those who participated in cognition-associated research activities in the previous 12.0 months were excluded from the analysis. The MedDiet-adhering individuals received one oz of almonds and three tablespoons of extra virgin olive oil daily.

The theories of social determination and social cognition were used to guide adherence to the study interventions. In addition, participants underwent hands-on (meal preparation) and didactic dietary training. All individuals were advised to attain moderate-vigorous physical activity levels at 150.0 minutes weekly. The control group participants received general health newsletters weekly.

Results

The dietary interventions did not significantly impact the LMR, EF, AIP, or MoCA scores. The mean increase in scores for adherence to the MedDiet plus calorie limitation and MedDiet alone interventions were 6.30 points and 4.80 points, respectively, in relation to the control group (+0.60 points).

The mean reductions in weight among individuals in the MedDiet plus calorie limitation group, the MedDiet alone group, and the control group were 4.60 kg, 2.60 kg, and 0.60 kg, respectively.

The dietary interventions showed no significant influence on the physical exercise and cardiometabolic biomarker levels, although lower fasting insulin levels and lower body weight values were observed in the MedDiet plus calorie limitation group participants compared to the other groups.

Particularly, a significant decrease in visceral adiposity was observed; however, the percentage of total body fat did not differ significantly among the groups post-intervention. Both intervention group participants had similar attendance for group sessions, and 67.0% of the study participants were hypertensive.

Conclusions

The study findings showed that MedDiet adherence with or without calorie limitation had no significant influence on cognition. However, the MedDiet interventions significantly reduced central obesity and body weight and improved dietary quality.

The cognitive benefit of adherence to MedDiet with or without limiting calorie intake could be associated with preventing or retarding pathological cognitive aging instead of maintaining normal cognitive aging.

Alternatively, the strength of the effect could have been lowered due to the use of different cognitive assessment scores instead of one composite score. Moreover, the limited sample size and short duration of interventions could have lowered the impact of the dietary interventions.

Further research must be conducted using objective dietary evaluations, larger sample sizes, and longer intervention durations for accounting for the alteration in the nutritional intake of processed food items in MedDiet.