Cognitive decline is less likely in those who follow a Mediterranean diet, according to a French study of 840 people aged 65 and over.

Dementia such as Alzheimer's disease and other neurodegenerative conditions often start with cognitive decline, which is a slow loss of mental abilities.

Research suggests that eating habits, especially the Mediterranean diet, may help protect against this loss.

Inspired by foods traditionally eaten across regions including Crete, Italy, and southern Spain, the Mediterranean diet prioritizes the consumption of fruits and vegetables, unprocessed cereals, some fish and cheese, and olive oil.

Evidence points to a number of benefits from such a mix of foods, including – potentially – a boost to our brain health.

There have been conflicting results, though, possibly due to the use of self-reported dietary questionnaires, which are prone to inaccuracies.

Studies have linked certain biomarkers to cognitive health, so an international group of researchers took this approach, which they propose is a more accurate way to measure dietary exposure and its relationship to health outcomes.

"We found that adherence to [the] Mediterranean diet assessed by a panel of dietary biomarkers is inversely associated with long-term cognitive decline in older people," says first author Alba Tor-Roca, a nutritionist and public health scientist at the University of Barcelona.

Tor-Roca and colleagues delved into the association between the Mediterranean diet and cognitive decline in older adults via a thorough analysis of health and cognitive data collected over the course of 12 years.

A 14-point scale was used to create the Mediterranean diet metabolomic score (MDMS). This score is based on two possible dietary metabolomic biomarkers for seven important parts of the Mediterranean diet: vegetables, legumes, fruits, cereals, dairy, fish and fats.

Metabolomics is the study of small molecules called metabolites that are products of cellular processes. Their levels can change in response to disease, diet, and other environmental factors.

Scientists can learn about our health and find possible biomarkers of disease by measuring the levels of metabolites in a sample.

"Within the framework of the study, a dietary metabolomic index has been designed – based on biomarkers obtained from the participants' serum – on the food groups that form part of the Mediterranean diet," says nutrition and food scientist Cristina Andrés-Lacueva from University of Barcelona.

"Once this index is known, its association with cognitive impairment is evaluated."

Serum levels of specific substances including saturated and unsaturated fats, gut bacteria-produced polyphenols, and other plant chemicals were measured from participants' blood samples collected at the beginning of the study.

Over the course of twelve years, five neuropsychological tests were administered to participants to determine their cognitive ability or impairment.

The researchers found a protective association between the Mediterranean diet and cognitive decline in older individuals, based on scores and serum biomarkers.

Individuals who more closely adhered to the Mediterranean diet demonstrated significantly slower cognitive decline compared to those with lower adherence levels.

"These results support the use of these indicators in long-term follow-up assessments,'" says Tor-Roca, "to observe the health benefits associated with the Mediterranean diet or other dietary patterns and therefore, guide personalized counseling at older ages."

The study does have limitations, for example blood samples for metabolomics analysis were only available at baseline, so the team could not examine prior exposures or changes during the follow-up.

Nutritional effects on health are always complex, but overall, the findings reinforce the notion that dietary patterns can play a role in maintaining brain health and reducing the risk of cognitive impairment as we age.

"The development of dietary metabolic scores based on dietary patterns may help further refine dietary assessment measures," the authors write, "and will hopefully contribute to a better understanding of the biological mechanisms via which diet impacts cognitive health in the aging population."

The study has been published in Molecular Nutrition and Food Research.