Study links processed foods to targeted domain-specific cognitive decline

An unhealthy Western-style diet was associated with a faster cognitive decline in people with a genetic risk of Alzheimer's disease, according to new research led by Murdoch University and Alzheimer's Research Australia.

As the world grapples with the growing public health challenge of dementia, there has been increasing academic interest in identifying lifestyle factors which may help maintain people's brain health as they age.

"Diet is particularly interesting because it is often easily modifiable, but people may not respond to dietary patterns in the same way," said lead author Dr Carolina Blagojevic Castro, from Murdoch University's Centre for Healthy Ageing.

"In this study we investigated whether the types of food people regularly eat are associated with how their thinking abilities change as they get older," Dr Blagojevic Castro said.

Using data from the Western Australia Memory Study (WAMS), the research team followed 185 older adults from Perth for more than seven years and examined whether unhealthy and healthier dietary patterns were associated with changes in different areas of their cognition, while also considering individuals' genetic risk for Alzheimer's disease.

The team grouped the participant's diets into two main groups – a Western diet (unhealthy diet), consisting of food such as red and processed meat, chips, pizza, sweets, refined grains and beer, and a Prudent diet (healthy diet), consisting of things like fruit, vegetables, leafy greens, garlic, and whole grains.

None of the participants had diagnosed dementia when they entered the study, but they were tested for genetic susceptibility factors such as the apolipoprotein E (APOE) variant, the strongest common genetic risk factor for Alzheimer's disease.

Throughout the study, participants completed a series of cognitive tests to assess their attention, memory, executive function, language, recognition memory, and their general cognitive ability.

"Our main finding was that among people carrying the APOE ε4 allele, greater adherence to a Western dietary pattern was associated with a faster decline in attention over time," Dr Blagojevic Castro said.

"One of the most interesting findings was that the association with cognitive decline was not seen across the whole group but emerged specifically among APOE ε4 carriers."

"We did not find significant associations between the healthier Prudent dietary pattern and cognitive decline, or between the Western dietary pattern and cognitive decline among people who did not carry APOE ε4."

Dr Blagojevic Castro said the findings reinforced growing evidence that the relationship between diet and brain health was complex and not the same for everyone.

"What we eat may be one part of a much larger picture of healthy brain aging," she said.

Our findings highlight why research into individual differences is important – approaches to protecting brain health may ultimately need to consider both lifestyle and biological factors rather than assuming that one approach will work equally well for everyone."

Dr. Blagojevic Castro, Murdoch University

"However, our study is observational, so further research is needed before these findings can be translated into specific dietary recommendations based on genetic risk."

The study, Dietary Patterns and Cognitive Decline in Older Adults: Findings from the Western Australia Memory Study, was supported by The University of Western Australia, Macquarie University, Edith Cowan University, the University of Sydney, and Brazil's State University of Bahia.