Diets that are famously good for the heart are also associated with preserving cognitive function.

I’m talking about the Mediterranean diet (often rated the healthiest in the world) and its cousin the DASH diet, tweaked to specifically lower high blood pressure.

Studies suggest that these diets reduce the risk of dementia.

But how does it happen?

The simplest idea was that a healthy heart promotes a healthy brain. In other words, there’s a knock-on effect.

A new study, however, has put some meat on these bare theoretical bones.

Scientists from New York’s Columbia University “tested the hypothesis that healthy diet protects against dementia by slowing down the body’s overall pace of biological ageing”.

This makes sense when you consider that dementia, in the main, is an ageing-related disease. If your diet can slow the pace of ageing, warding off dementia would be a logical consequence.

More than that, once you can slow the pace of ageing, your risk of all manner of ageing-related diseases may be reduced.

The new study

According to a statement from Columbia University’s Mailman School of Public Health:

The researchers analysed data from the second generation of participants in the Framingham Heart Study, the Offspring Cohort.

Originating in 1971, participants in the Offspring Cohort were 60 years of age or older, and were free of dementia. The study also accessed available dietary, epigenetic, and follow-up data.

The participants were followed up at nine examinations, approximately every four to seven years.

At each follow-up visit, data collection included a physical examination, lifestyle-related questionnaires, blood sampling and, starting in 1991, neurocognitive testing.

Of 1644 participants included in the analyses, 140 of the participants developed dementia.

The speedometer

The diet tested in the study was a relatively new hybrid of the Mediterranean-Dash interventions known as the MIND diet. MIND focuses on foods that are believed to support brain health: whole grains, green leafy vegetables, nuts, beans and olive oil.

See more here.

Researchers measured the pace of biological ageing – how fast the participants’ bodies were deteriorating over time – using the DunedinPACE epigenetic clock.

This a tool that estimates ageing based on DNA methylation patterns. It’s often described as being like a speedometer for the biological processes of ageing.

The findings

Participants who adhered to the MIND diet were found to biologically age at a slower rate.

Specifically, “27 per cent of the diet’s protective effect against dementia was mediated through its impact on slowing biological ageing”.

In other words, a healthier diet keeps the body and brain “younger” for longer.

The research confirmed the relationship between diet, pace of biological aging, and the risk of death from any cause.

It found that “a slower pace of biological aging, influenced by diet, accounted for 57 per cent of the diet’s beneficial effect on lowering mortality risk”.

Dr Aline Thomas, is a Postdoc at the Columbia Department of Neurology and Taub Institute for Research on Alzheimer’s Disease and the Aging Brain. She is first author of the new paper. She said:

“Our findings suggest that slower pace of ageing mediates part of the relationship of healthy diet with reduced dementia risk, and therefore, monitoring pace of ageing may inform dementia prevention.”

However, she said, “a portion of the diet-dementia association remains unexplained, therefore we believe that continued investigation of brain-specific mechanisms in well-designed mediation studies is warranted”.

A previous study

In November, we reported on a fascinating study from Zhejiang University School of Medicine, and Harvard T. H. Chan School of Public Health.

The scientists found that higher adherence to the MIND diet was associated with “larger volumes” of certain parts of the brain.

This was in a study that analysed data of 26,466 middle-aged participants in the UK Biobank. The findings held regardless of genetic predisposition of Alzheimer’s disease.

The parts of the brain positively affected by the diet include those that play a role in regulating emotions; relaying sensory information (hearing, taste, sight and touch, but not smell) to the respective parts of the brain responsible for their processing; and facilitating movement.

As we age, our brains tend to shrink. That these parts of the brain actually got bigger suggests that ageing wasn’t slowed, but reversed.