Under the Microscope: Improving Health and Nutrition in America

Does Diet Affect Long Term Brain Health?

In this new series, we discuss ground-breaking research being conducted on human nutrition, paving the way for Americans to lead healthier lives while reducing the risk of diseases. ARS funded research supports human health at all stages of life by better understanding relationships between nutrient intake, eating patterns, exercise, health conditions, disease prevention, and how nutrition promotes health.

In this article, we look at possible associations between different dietary patterns and brain aging. Our guests are Dr. Sarah Booth, Center Director and Senior Scientist for the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston, MA, and Dr. Paul Jacques, Senior Scientist at the Jean Mayer Center. Drs. Booth and Jacques recently completed a review titled, “Dietary Patterns and Brain Aging: Enthusiasm Before Evidence?”

Pictured Left to Right:  Dr. Sarah Booth and Dr. Paul Jacques

Welcome to Drs. Booth and Jacques to Under the Microscope:

UM: Before conducting the study, what did you already know from previous research on associations between brain aging and diet?

SB/PJ: Research suggests that what we eat may help slow down memory loss and lower the risk of Alzheimer’s disease and related conditions. In this study, we looked at and summarized existing research on how healthy diets are connected to changes in the aging brain, both normal changes and those linked to disease. We also evaluated how strong and reliable that evidence is and pointed out areas where more research is needed to better understand how diet affects brain aging.

UM: What did your study confirm or change about this linkage?

SB/PJ: Our findings support the evidence that healthy dietary patterns, which include higher consumption of vegetables, fruits, legumes, nuts, fish and other seafood, and unsaturated vegetable oils and lower consumption of red and processed meats and sugar-sweetened beverages, are associated with lower risk of age-related neurodegenerative disease.

Family eating healthy. (Getty stock photo)

While there is some promising evidence, many of the existing studies have important limitations. For example, researchers use different tests to measure memory and thinking, and study groups vary widely in their health and cognitive status, making it hard to compare results. Some studies may also have biases or inaccuracies—for instance, people may not report their diets perfectly, and early memory problems could already be affecting what they eat. Another issue is that many studies don’t track how people’s diets change over time, so they may miss important shifts in dietary patterns. Finally, much of the research focuses on older adults, which makes it harder to understand whether eating habits earlier in adulthood might have a bigger impact on preventing cognitive decline.

UM: For Americans looking to avoid cognitive diseases later in life, is it as simple as eating more vegetables, fruits, legumes, nuts, fish and/or seafood, and unsaturated vegetable oils/fats and less red and processed meats and sugar-sweetened beverages?

SB/PJ: While there are still gaps in our understanding of the role of diet and brain aging, we know that healthy diet patterns lower risk of conditions such as diabetes and other cardiovascular disease risk factors, which are also risk factors for cognitive decline and dementia.  However, it is unlikely that consumption of a healthy dietary pattern alone will achieve clinically relevant success in reducing risk of cognitive decline and/or dementia given the many risk factors other than diet that are associated with variation in age-related cognitive decline and dementia risk.

UM: What other risk factors play a part in cognitive decline and associated diseases such as Alzheimer’s and dementia?

SB/PJ: Age is the single biggest risk factor for Alzheimer’s disease and related dementias—the chances of developing it roughly double every 5 years between ages 65 and 90. Sex also plays a role, with women having about twice the risk of men. Other known risk factors include a history of serious head injury and carrying a certain genetic trait called ApoE4. However, these risks can’t be changed.

Conversely, some risk factors are modifiable. In addition to diet, these include heart and metabolic health conditions like diabetes, high blood pressure, high cholesterol, and obesity, as well as lifestyle factors such as physical activity, alcohol use, smoking, education level, and social connections.

UM: Can improving your diet later in life help lower the risk of cognitive decline?

SB/PJ: While our study did not directly address this issue, there is limited evidence that individuals in their 60’s and 70’s who consumed a healthier diet have less risk of dementia. However, we are not aware of any studies showing that improvements in diet in individuals in their 80’s and older lowers dementia risk.

Seniors eating healthy. (Getty stock photo)

Given that the pathological processes that ultimately lead to dementia are believed to start 20 to 30 years prior to the diagnosis of dementia, consuming a healthier diet at younger and middle ages may provide the best opportunity to prevent or delay the onset of pathological cognitive decline. That said, it would be reasonable to suggest that a healthier diet could help maintain cognitive health for older individuals of any age who have yet to experience cognitive decline.

UM: Your study discussed a possible link between type 2 diabetes and dementia. Please elaborate.

SB/PJ: Type 2 diabetes is a known risk factor for Alzheimer’s disease and related dementias. It develops when the body becomes resistant to insulin, a hormone that helps control blood sugar. Insulin resistance can also happen in the brain itself, and this may play an important role in the development of Alzheimer’s disease. Importantly, insulin resistance in the brain is not the same as insulin resistance in the rest of the body, and it can occur even in people who do not have type 2 diabetes.  It is an emerging area but requires more research to unravel the underlying mechanisms that link it to Alzheimer’s disease and related dementias.

UM: Do the consumption of individual nutrients, such as polyphenols and vitamins D and K, play a role in reducing the risk of cognitive diseases later in life? If so, are there also risks to overconsuming these nutrients?

SB/PJ: There is evidence that several individual nutrients may play a role in brain health, but adequate intakes of most of these nutrients, including the polyphenols, lutein, vitamin K, choline, polyunsaturated fatty acids, and other dietary bioactive compounds, are readily achieved in healthy dietary patterns that include a variety of plant foods (including whole grains), fish and other seafoods, dairy, healthy oils, and limit refined gain products, saturated fats, and added salt and sugar.  While each nutrient might have small individual effects on cognitive function, together in a healthy diet, their combined effects could provide much greater benefits, negating the need for consuming multiple supplements. This is consistent with studies of diet patterns, which generally show stronger and more consistent protective associations than seen with individual nutrients. 

Two exceptions where supplements may be beneficial are vitamins B12 and D, particularly for older individuals who may experience greater inadequacies of these vitamins.    

UM: Your study mentions several diets, including the Mediterranean-style diet, the Dietary Approaches to Stop Hypertension (DASH) diet, and the Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diet. What were your conclusions from studying these diets?

SB/PJ: The research shows that all these healthy eating patterns are linked to better brain health and a lower risk of Alzheimer’s disease and related dementias. This isn’t surprising because these diets are quite similar, even though they emphasize slightly different foods. All of these diets encourage eating plenty of plant-based foods like fruits (especially berries), vegetables (especially leafy greens), beans, nuts, seeds, and whole grains. They also recommend using healthy fats like olive oil. Fish and poultry are included in moderate amounts, while red and processed meats, as well as sweets and pastries, should be limited.

Mediterranean-style food. (Getty stock photo)

There are a few differences—for example, the DASH diet includes more low-fat dairy, the Mediterranean diet allows moderate dairy, and the MIND diet mainly recommends limiting cheese and butter. The main takeaway is that there isn’t just one “perfect” diet. Healthy eating can look a little different for everyone, but in general, it should focus on mostly plant-based, minimally processed foods; include smaller amounts of healthier animal foods; and limit processed foods that are high in salt, unhealthy fats, and added sugars. This concept that healthy diets can take different forms is important for helping people adhere to dietary recommendations. It allows for cultural, medical, and personal preferences, and shows that there are many ways to eat healthfully—more than we may have previously thought.

UM: What is the big takeaway for Americans in each age group?

SB/PJ: The importance of diet in neurodevelopment and cognitive health of infants, children, adolescents, and young adults is established, and evidence is accumulating to suggest that diet may affect brain aging as well. Despite our incomplete understanding of the latter, we know that healthy diets can have important impacts on many different health outcomes across the lifespan so we should not only focus on the role of diet on the brain but also on the role of diet in overall healthy aging.