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Eating a predominantly plant-based diet may substantially slow the rate of cognitive decline in older Black adults in the U.S., according to preliminary research.

However, this dietary pattern had less effect on cognitive decline in older white adults, according to the presented Friday at the ľ¹ÏÖ±²¥'s Epidemiology and Prevention, Lifestyle and Cardiometabolic Health conference in Chicago.

"It's not that the diet doesn't work on white people," said lead researcher Xiaoran Liu, an assistant professor at Rush University Medical Center's Institute for Healthy Aging in Chicago. "It just had a greater impact on African Americans."

Previous studies have found healthy dietary changes can slow cognitive decline, but little research looked at the impact on Black adults, who face roughly twice the risk for dementia as white adults. Other studies have linked a predominantly plant-based diet to a lower risk for stroke, heart disease and Type 2 diabetes.

"Science is really coming out to support the importance of a healthy plant-based diet," said Maya Vadiveloo, an assistant professor of nutrition and food sciences at the University of Rhode Island. "It doesn't mean we can't have any animal-sourced foods or low-fat dairy, but people should focus on eating more legumes and whole grains. These plant-based foods are really important for our overall health."

In the new study, researchers analyzed diet and cognitive performance over a decade for 4,753 Black and white adults who were 74 years old on average at the start of the study. Based on their scores from self-reported dietary patterns, participants were divided into three groups: those with healthy plant-based diets high in fruits, vegetables, nuts, whole grains, legumes, vegetable oils, tea and coffee; those who ate a less-healthy plant-based diet that included fruit juices, refined grains, potatoes, sugar-sweetened beverages and sweets; and those who ate a diet with animal fats, dairy, eggs, meats, fish or seafood. Overall, Black adults in the study ate more eggs, fish or seafood, sugary drinks and whole grains than their white peers.

Researchers then used tests to measure overall cognition, perceptual speed and episodic memory – the ability to recall personal experiences associated with a particular time and place. The findings showed the healthiest plant-based diet slowed the decline more in all three areas for Black adults than it did for white adults.

Overall cognitive decline slowed by 28.4% among Black adults in the highest bracket of the healthiest eating group compared to their Black peers whose plant-based diet wasn't as healthy. Black and white adults in the other two dietary categories showed no slowing of overall cognitive decline.

The impact of diet on perceptual speed and episodic memory was even more dramatic for Black adults. Those who ate the healthiest plant-based diet experienced a 49.3% slower decline in perceptual speed and a 44.2% slower decline in episodic memory than their peers who ate a diet with more animal foods. The findings are considered preliminary until a full study is published in a peer-reviewed journal.

There could be many explanations for the disparity between white and Black adults, Liu said. One reason may be Black adults are at , which affect cognitive health, so reducing that risk by eating a heart-healthy, plant-based diet may have a more pronounced impact on their brain health than on people whose risk is lower to begin with.

Black people in the United States face those higher cardiovascular risks for a number of reasons, including systemic and societal issues that historically have limited access to care, medication, nutritious foods and other resources that can lower risks.

Liu said the disparity in cognitive decline in the study also could be caused by eating patterns. For example, Black adults ate a lot more whole grains than white adults. She is currently analyzing the impact of specific food groups on participants' cognitive decline.

Vadiveloo, who was not involved in the new research, said she hoped findings like this would motivate people to eat a healthier diet. "Sometimes people are motivated by different health conditions differently. Dementia is pretty motivating for adults, maybe even more so than heart disease."

Vadiveloo co-authored an AHA last November offering dietary guidance to improve heart health. The statement emphasizes the importance of eating a wide range of fruits and vegetables along with whole grains, fish and seafood.

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