There is no shortage of articles online that provide dietary suggestions for brain-healthy foods. Some of those reports refer to observational studies that imply a link between the consumption of particular foods and the risk of dementia.

Clinical studies, however, have not shown strong evidence linking particular diets or nutrients to cognitive function.

Hussein Yassine, MD, associate professor of medicine and neurology at the Keck School of Medicine of USC and the Kenneth and Bette Volk Chair of Neurology of USC, indicated that “many trials have not found that making people eat healthy or exercise is translating into benefits in the ways that is expected from the epidemiological research.” 

That indicates that there is either no causal relationship or that these research were not properly constructed.

Yassine was the leader of the Diet for Dementia Prevention Working Group, a group of scientists who spent two years reviewing the literature on nutrition and dementia risk in order to comprehend this gap between epidemiological studies and clinical trials. Their analysis, which was just published in The Lancet Healthy Longevity, points out significant flaws in current studies that affect how nutrition impacts the brain and provides recommendations for future research. This research was funded by a National Institutes of Health grant (NIH).

Nutritional research challenges

Yassine makes the point that it can be challenging to do quality nutrition research in general. According to epidemiological research, those who consume fatty seafood, such as salmon, had a decreased risk of dementia. However, it can be difficult to distinguish between nutritional information and other variables that may also be at play, such as a person’s location, concurrent healthy lifestyles, or their access to quality medical care.

Most of the clinical trials on food and brain health may not have been done for long enough for the results to be useful, because no one knows how long it takes for a healthy diet to affect cognition. “If it takes five to 10 years,” added Yassine, “then studies that lasted for two years or less are not accurately reflecting the effect of the diet on cognition.” 

Future studies will also advance if it is determined how much of a certain vitamin an individual requires to have optimal brain health. For instance, there is a recommended amount of vitamin D that keeps bones healthy, but the same cannot be said for minerals that are known to affect cognitive health.

Accepting new research and technologies

The group makes the point that using biomarkers instead of cognitive tests, which are typically used to assess the effectiveness of an intervention, may produce more significant early results that can direct more extensive treatments that focus on clinical outcomes. The use of technology, such as brain imaging, can be very useful in observing how the brain evolves over time. They also note that checking blood or stool samples for particular biomarkers, such as inadequate consumption of a particular nutrient, can be used to both choose the best volunteers and ascertain how well study subjects respond to the intervention being tested.

Yassine, who researches apolipoprotein E4, or APOE4, the strongest genetic risk factor for late-onset Alzheimer’s disease, claims that genetic testing can also be a useful tool. He pointed out that those who carry this version of the gene have a different reaction to food than those who do not. In this case, genetic testing can lead to better studies and more precise treatment plans.

Microbiome research can improve research outcomes. According to Yassine, dietary benefits vary from person to person due to variations in the microbiota. “You cannot fully study how the diet is working without studying the microbiome,” according to Yassine.   Additionally, there is a need for greater comprehension of the underlying connection between cognition in sizable groups of diverse people and the gut microbiome.

New ways of thinking

Finally, the panel came to the conclusion that researchers should think about using a wider variety of study designs, not simply randomized controlled trials, and that trial participant selection has to be given more consideration.

They point out that one tactic would be to create small, individualized studies that take participants’ genetic susceptibility, the quality of their diet, and an examination of their microbiome into account while using biomarkers that represent brain functioning. Another strategy involves creating sizable, realistic electronic health trials targeted at persons with dementia risk factors and using mobile phones or tablets to collect data.

While older adults have been the focus of the majority of research to date, several high-quality cohort studies indicate that middle age may be the best time to start this type of research because it is before the onset of changes associated with dementia, allowing researchers to monitor changes over time. The group also emphasizes the necessity for studies to take into account the eating habits of underrepresented groups, some of which are disproportionately affected by dementia.

According to Lon Schneider, MD, Professor of Psychiatry and the Behavioral Sciences at the Keck School of Medicine and Della Martin Chair in Psychiatry and Neuroscience, “this is an important document for anyone doing research on diet and how it relates to dementia.” 

“It is important that future trials yield accurate results that can be translated into better clinical care for patients.” 

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