The Mediterranean diet not only has beneficial effects on the cardiovascular health of people who follow it, but can also enable them to improve their memory and prevent or delay the effects of cognitive impairment associated with ageing. However, these beneficial effects do not reach everyone equally, which leads to the need for changes in the type of interventions based on dietary recommendations to adapt them to the characteristics of each individual. These are the main results of a study published in Clinical Nutrition, led by researchers from the Integrative Pharmacology and Systems Neuroscience Group and the Cardiovascular Risk and Nutrition Group of the Hospital del Mar Medical Research Institute (IMIM-Hospital del Mar) along with the Psychiatry and Mental Health Group of the Bellvitge Biomedical Research Institute (IDIBELL) and the Bellvitge University Hospital, all part of the CIBER on Physiopathology of Obesity and Nutrition (CIBEROBN). The Universitat de València, the Rovira i Virgili University and the University of Navarra have also taken part in this project.

For three years, the study followed a group of 487 volunteers, almost equally divided between men and women and with an average age of 65 years. All were participants in the PREDIMED-PLUS (PREvenciónDIetaMEDiterranea Plus) trial, a multicentre study involving 23 research centres in Spain that analises the effect of the traditional Mediterranean diet along with energy restriction, promotion of physical activity and behavioural intervention on weight loss and cardiovascular disease prevention. At the beginning of the study, participants were overweight or obese and fulfilled at least three criteria of metabolic syndrome, which includes hypertension, hyperglycaemia, excess fat around the waist, low HDL-cholesterol levels and high triglyceride levels. Metabolic syndrome is very common, being present in about 1 in 4 adults worlwide. It involves a greater risk of heart diseases, strokes, type-2 diabetes and cognitive impairment.

Improving adherence to the diet, enhances our memory

Using neuropsychological tests, researchers analysed the cognitive state of volunteers at the beginning of the study and after one and three years, respectively. Their performance in memory and other cognitive functions, including the ability to make decisions, reason, pay attention, plan or ignore certain impulses, was established.

According to previous studies, over a three-year period, people with metabolic syndrome who do not follow any type of intervention would have presented a decrease of almost 0.40 points in their overall cognition and 0.10 points in their memory. In contrast, with the study recommendations, they registered improvements of more than 0.60 points in their overall cognition and around 0.90 in their memory. Units of measurement of cognition are standardised in order to be able to compare neuropsychological tests that are on different scales.

In patients as a group, the results denote a direct relationship between adherence to the Mediterranean diet and cognitive improvement. Adherence to the low-calorie Mediterranean diet is measured with a 17-item survey that explores extra-virgin olive oil consumption and the number of servings of vegetables and pieces of fruit consumed per day, among others. Scores above 11 points are considered to have a high adherence to the Mediterranean diet. Thus, for each point of improvement in adherence to this type of diet, their memory improved by 0.13 points. According to the research, this improvement may stem from weight loss and increased physical activity, which is also associated with an enhanced quality of life. In this sense, Rafael de la Torre, one of the main researchers of the study, points out that “this is an important fact, taking into account that cognitive changes may not be perceptible to people, but may be more relevant if combined with enhancements in their quality of life”.

For his part, Fernando Fernández-Aranda, project leader from the IDIBELL and Bellvitge Hospital, indicates that “thanks to this study we have been able to define the advantages of the Mediterranean diet beyond weight loss, such as verbal memory or attention, which clearly benefit from it”.

Not everyone benefits equally from it

“More adherence to the Mediterranean diet implies a greater improvement in cognition”, explains Natàlia Soldevilla-Domènech, first author of the study. But benefits are not the same for everyone. Women, older people, those who have a lower educational level and those with type-2 diabetes are groups that benefit less from following the Mediterranean diet. Regarding this fact, the researcher points out that “although we see that women have a lower improvement in cognition compared to men, these cognitive enhancements occurred in the participants as a whole. Everyone benefits from following the Mediterranean diet, but to a greater or lesser degree”.

At the same time, volunteers with a lower cognitive performance in memory and other cognitive functions at the beginning of the study are the least likely to adhere to the Mediterranean diet and the least likely to achieve a significant weight loss. “From a cognitive and behavioural viewpoint, we were interested in knowing which volunteers lost weight and which did not, and why some did and others did not”, explains Rafael de la Torre. Specifically, people who at the beginning of the study had a better auditory memory, better planning and decision-making skills, shorter reaction time and less impulsivity were 20-50% more likely to achieve the study goal of losing an 8% of their weight over three years. According to the research, this is due to the fact that most people with these cognitive abilities achieved high adherence to the low-calorie Mediterranean diet, which resulted in clinically relevant weight loss.

For these reasons, the authors point out that the results obtained should enable the identification of groups with the greatest difficulties in benefiting from these lifestyle interventions, in order to customise the measures and thus facilitate their adoption of the proposed healthy lifestyle patterns, while at the same time favouring the prevention of cognitive impairment.

The study has been funded by national research agencies, including the Institute of Health Carlos III and the Catalan government (Generalitat de Catalunya), as well as by European funds (Eat2BeNice project).

Reference article

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