Can a healthy diet really prevent dementia?

By Simon Spichak, MSc | August 10, 2022

A healthy diet appears to prevent dementia. Why is it so hard to prove?

It’s always difficult to accurately track what people eat over long periods of time. It is even more difficult to link this data to brain health. A panel of experts says the answer may lie in better clinical trial design.

The number of people with dementia should more than triple by 2050, reaching 152 million cases worldwide. Not all types of dementia are preventable, but growing evidence points to the possibility that some cases are. With certain environmental and lifestyle interventions, this “some” could be as substantial as two out of five cases of dementia delayed or avoided. When it comes to a set of precise and clear instructions on How to Prevent Dementiahowever, the research leaves much to be desired.

For example, there was a lot of talk after the Alzheimer’s Association international conference last week about early data from a 60-year-old study of how highly processed foods may accelerate cognitive decline in the elderly. On the other hand, some researchers are “certain” that good nutrition reduces the risk of future cognitive impairment and dementia. But despite decades of study, there is still a broad consensus that the links between brain function and foods or food groups are not yet conclusive. With such encouraging evidence, why is the idea of ​​a “dementia prevention diet” so hard to prove?

Recently, a Nutrition for Dementia Prevention Task Force made up of 27 leading researchers in the field of Alzheimer’s disease and dementia came up with recommendations to help solidify the science around the relationship between diets and reducing the risk of dementia. The group guidelines were published in The Lancet Health Longevitywhere the authors also point out the limitations of existing research.

“Many trials have not shown that feeding healthily or exercising translates into benefits in the way that epidemiological research would expect,” said Dr. Hussein Yassine, associate professor of medicine and in Neurology at USC’s Keck School of Medicine, said in a press release. “That either means there’s no causal link, or these studies weren’t properly designed.”

Studying nutrition: it’s complicated

The researchers involved in creating these guidelines spent two years reviewing the large body of evidence linking nutrition and dementia risk. The results of nutritional research, they found, are not always straightforward. For example, we know that a Mediterranean style diet is healthy and that study participants who adhere to this diet are less likely to develop Alzheimer’s disease or other forms of dementia. But is the regime itself the protector? Or are there other factors at work behind the scenes?

What if, for example, the consumption of a Mediterranean diet was linked to another influencing but unmeasured factor, such as Socioeconomic statuswhich is also linked to brain health?

In addition to unmeasured variables, Yassine notes that studies can often be too short to spot significant effects of a dietary intervention on cognition. “If it takes five to 10 years,” he said, “then studies that lasted two years or less don’t accurately reflect the effect of diet on cognition.”

Studies that have hung on there for an entire decade have yet found a positive correlation between a healthy diet and a lower risk of Alzheimer’s disease and dementia. But the recommendations of the working group go beyond the simple extension of studies.

Using brain biomarkers to analyze the impact of healthy eating

Countless studies explore the relationship between consumption of nutrients (like folate, flavonoids, vitamin D, and certain lipids) or food groups (like seafood, vegetables, and fruits) and cognitive health. , giving unstable results. There is no consensus on, for example, the optimal levels of certain vitamins or nutrients as they relate to brain health.

The authors argue that taking advantage of biomarkers of brain imaging, blood tests and can provide valuable insight into how foods and nutrients are processed by the body and how they can impact the brain. Overlooking these biomarkers in participants is where some studies fail, according to Yassine. “You can’t fully study how the diet works without studying the microbiome,” he said.

The researchers also suggested, in addition to the current gold standard of large randomized controlled trials, to use other types of trials as well. Rather than just looking at a participant group of 100,000 people, the authors say, smaller, personalized studies could help shed light on more nuanced factors, such as genetic risk, diet and the microbiome of an individual, and their relationship to brain health. The task force also argues that this preventive research regarding diet and dementia risk should begin in participants’ 40s, before symptoms of Alzheimer’s disease or dementia set in.

By measuring these biomarkers, collecting information on other risk factors, and carefully tracking diet and nutritional intake, it may be possible to finally answer how and why diet protects against dementia. There might finally be a clear and conclusive answer as to which foods are most protective for people with a specific risk factor, or whether a person is getting enough of a specific vitamin or nutrient to maintain brain health. .

According to Dr. Lon Schneider, professor of psychiatry and behavioral sciences at the Keck School of Medicine, the better the design of trials can be, the more likely people are to prevent Alzheimer’s disease and dementia.

“It is important that future trials yield accurate results,” he said, “that can translate into better clinical care for patients.

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