Higher diet quality is associated with greater cognitive reserve in midlife

A new study published in Current Developments in Nutrition provides evidence that individuals who adhere to higher quality diets, particularly those rich in healthy plant-based foods, tend to possess greater cognitive reserve in midlife. This concept refers to the brain’s resilience against aging and disease, and the findings suggest that what people eat throughout their lives may play a distinct role in building this mental buffer.

As humans age, the brain undergoes natural structural changes that can lead to difficulties with memory, thinking, and behavior. Medical professionals have observed that some individuals with physical signs of brain disease, such as the pathology associated with Alzheimer’s, do not exhibit the expected cognitive symptoms. This resilience is attributed to cognitive reserve, a property of the brain that allows it to cope with or compensate for damage.

While factors such as education level and occupational complexity are known to contribute to this buffer, the specific influence of dietary habits has been less clear. The scientific community has sought to determine if nutrition can serve as a modifiable factor to help individuals maintain cognitive function into older age.

“It has been established that cognitive reserve is largely influenced by factors like genetics, education, occupation, and certain lifestyle behaviors like physical activity and social engagement,” explained study author Kelly C. Cara, a postdoctoral fellow at the American Cancer Society.

“Few studies have examined the potential impact of diet on cognitive reserve, but specific dietary patterns (i.e., all the foods and beverages a person consumes), foods, and food components have been associated with other cognitive outcomes including executive function and cognitive decline. With this study, we wanted to determine whether certain dietary patterns were associated with cognitive reserve and to what degree diet quality may influence cognitive reserve.”

For their study, the researchers analyzed data from the 1946 British Birth Cohort. This is a long-running project that has followed thousands of people born in Great Britain during a single week in March 1946. The final analysis for this specific study included 2,514 participants. The researchers utilized dietary data collected at four different points in the participants’ lives: at age 4, age 36, age 43, and age 53. By averaging these records, the team created a cumulative picture of each person’s typical eating habits over five decades.

The researchers assessed these dietary habits using two main frameworks. The first was the Healthy Eating Index-2020. This index measures how closely a person’s diet aligns with the Dietary Guidelines for Americans. It assigns higher scores for the consumption of fruits, vegetables, whole grains, dairy, and proteins, while lowering scores for high intakes of refined grains, sodium, and added sugars.

The second framework involved three variations of a Plant-Based Diet Index. These indexes scored participants based on their intake of plant foods versus animal foods. The overall Plant-Based Diet Index gave positive scores for all plant foods and reverse scores for animal foods.

The researchers also calculated a Healthful Plant-Based Diet Index, which specifically rewarded the intake of nutritious plant foods like whole grains, fruits, vegetables, nuts, legumes, vegetable oils, tea, and coffee. Finally, they calculated an Unhealthful Plant-Based Diet Index. This measure assigned higher scores to less healthy plant-derived options, such as fruit juices, refined grains, potatoes, sugar-sweetened beverages, and sweets.

To measure cognitive reserve, the researchers administered the National Adult Reading Test to the participants when they were 53 years old. This assessment asks individuals to read aloud a list of 50 words with irregular pronunciations. The test is designed to measure “crystallized” cognitive ability, which relies on knowledge and experience acquired over time.

Unlike “fluid” abilities such as processing speed or working memory, crystallized abilities tend to remain stable even as people age or experience early stages of neurodegeneration. This stability makes the reading test a reliable proxy for estimating a person’s accumulated cognitive reserve.

The analysis revealed that participants with higher scores on the Healthy Eating Index and the Healthful Plant-Based Diet Index tended to have higher reading test scores at age 53. The data suggested a dose-response relationship, meaning that as diet quality improved, cognitive reserve scores generally increased.

Participants in the top twenty percent of adherence to the Healthy Eating Index showed the strongest association with better cognitive reserve. This relationship persisted even after the researchers used statistical models to adjust for potential confounding factors, including childhood socioeconomic status, adult education levels, and physical activity.

“This was one of the first studies looking at the relationship between dietary intake and cognitive reserve, and the findings show that diet is worth exploring further as a potential influencer of cognitive reserve,” Cara told PsyPost.

On the other hand, the researchers found an inverse relationship regarding the Unhealthful Plant-Based Diet Index. Participants who consumed the highest amounts of refined grains, sugary drinks, and sweets generally had lower cognitive reserve scores. This distinction highlights that the source and quality of plant-based foods are significant. The findings indicate that simply reducing animal products is not sufficient for cognitive benefits if the diet consists largely of processed plant foods.

The researchers also examined how much variability in cognitive reserve could be explained by these dietary patterns. The single strongest predictor of cognitive reserve at age 53 was the individual’s childhood cognitive ability, measured at age 8. This early-life factor accounted for over 40 percent of the variance in the adult scores.

However, the Healthy Eating Index scores still uniquely explained about 2.84 percent of the variation. While this number may appear small, the authors noted that when diet was combined with other lifestyle factors like smoking and exercise, the collective contribution to cognitive reserve was roughly 5 percent. This effect size is comparable to the cognitive advantage associated with obtaining a higher education degree.

“People in our study with healthier dietary patterns generally showed higher levels of cognitive reserve while those with less healthy dietary patterns generally showed lower levels of cognitive reserve,” Cara explained. “We do not yet know if diet caused these differences in cognitive reserve or if the differences were due to some other factor(s). Our study findings did suggest that diet plays at least a small role in individuals’ cognitive reserve levels.”

It is worth noting that the Healthy Eating Index showed a stronger association with cognitive reserve than the plant-based indexes. The authors suggest this may be due to how the indexes treat certain foods. The Healthy Eating Index rewards the consumption of fish and seafood, which are rich in omega-3 fatty acids known to support brain health. In contrast, the plant-based indexes penalize all animal products, including fish.

Additionally, the plant-based indexes categorized all potatoes and fruit juices as unhealthful. The Healthy Eating Index allows for these items to count toward total vegetable and fruit intake in moderation. This nuance in scoring may explain why the general healthy eating score served as a better predictor of cognitive outcomes.

As with all research, there are some caveats to consider. The measurement of cognitive reserve was cross-sectional, meaning it looked at the outcome at a single point in time rather than tracking the development of reserve over decades. It is not possible to definitively state that the diet caused the higher test scores, as other unmeasured factors could play a role. For instance, while the study controlled for childhood cognition, it is difficult to completely rule out the possibility that people with higher cognitive abilities simply choose healthier diets.

“To date, very few studies have examined diet and cognitive reserve, so our work started with an investigation of the relationship between diet and cognitive reserve only at a single point in time,” Cara said. “While we can’t draw any strong conclusions from the findings, we believe our study suggests that diet may be one of the factors that influence cognitive reserve.”

“Future studies that look at diet and the development of cognitive reserve over time will help us better understand if dietary patterns or any specific aspect of diet can improve or worsen cognitive reserve. I hope to apply different statistical approaches to dietary and cognitive data collected across several decades to get at how these two factors relate to each other over a lifetime.”

The study, “Associations Between Healthy and Plant-Based Dietary Patterns and Cognitive Reserve: A Cross-Sectional Analysis of the 1946 British Birth Cohort,” was authored by Kelly C. Cara, Tammy M. Scott, Paul F. Jacques, and Mei Chung.