Eating more plants linked to lower risk of dementia, even in older age

By Sandee LaMotte, CNN

(CNN) — Eating a high-quality plant-rich diet that includes whole grains, vegetables and fruits may prevent cognitive impairment — even when people start that diet in their late 50s and 60s, according to a new study.

“It’s never too late to start eating healthy to lower the risk of Alzheimer’s disease and related dementias,” said senior author Unhee Lim, a professor of population sciences at the University of Hawaii Cancer Center in Honolulu, in an email.

Older adults who cut many unhealthy foods from their diet over a decade had a 11% lower risk of Alzheimer’s and dementia when compared with adults whose diets didn’t change, Lim said.

However, people who increasingly ate more unhealthy plant-based options, such as refined grains and foods with added sugars, were about 25% more likely to develop some type of dementia at the end of 10 years, she said.

“The findings suggest that both plant-predominant eating and high diet quality help protect brain function as we age,” said Dr. David Katz, a specialist in preventive and lifestyle medicine who was not involved with the study. Katz founded the nonprofit True Health Initiative, a global coalition of experts dedicated to evidence-based lifestyle medicine.

What is a ‘healthy’ plant-based diet?

The basic definition of a plant-based diet is broad, simply requiring a person to prioritize eating more plant foods than animal products such as meat, milk and eggs. Under that umbrella, a person could call themselves a vegan and yet subsist on sugary, fat-filled, ultraprocessed foods known to harm health.

Breakfast, for example, could be an ultraprocessed frozen waffle or pancake with fake maple syrup. Lunch could include a fast-food veggie burger high in sodium, french fries or onion rings dripping in saturated fat, and a fruit-based soda packed with sugar. Dinner could include refined-grain white flour pasta with high-sugar tomato sauce, followed by ultraprocessed cookies or cake — all plant-based, but none good for your brain’s health.

The new report, published Wednesday in the journal Neurology, tried to tease apart how the quality of a plant-based diet would impact dementia risk. The study included nearly 93,000 people with an average age of 59 and a diverse mix of ethnicities: African American, Japanese American, Latino, Native Hawaiian and White. All participants were asked about their diets at the start of the study. Ten years later, a smaller group of just over 45,000 people reported on their diet a second time.

The research team scored diets on three tiers of quality. Eating saturated animal fats, dairy, eggs, seafood and meat was the lowest tier. A tier up was less healthy plant-based foods such as refined grains, fruit juices, potatoes and added sugars.

Why are fruit juices and potatoes considered less healthy? Potatoes are high in starch, which quickly turns into glucose in the blood, potentially triggering blood sugar spikes. In addition, frying potatoes or adding sour cream and butter adds excessive calories, unhealthy fats and sodium.

Drinking fruit juice such as apple or orange, for example, floods the blood with fructose, a sugar found naturally in fruits and some vegetables. Eating a whole apple or orange, on the other hand, doesn’t spike blood sugar levels in the same way because the fiber inherent in the fruit slows the release of fructose into the blood.

The top tier were the healthiest plant foods — whole grains, fruits, vegetables, vegetable oils, nuts, legumes, and tea and coffee. Eating more of these plants was most protective for the brain, the researchers found.

When a subgroup of people who ate the healthiest plant-based foods were compared with each other, those who ate the most plants in this tier lowered their risk of dementia by 7% compared with those who ate the least.

Among the subgroup who ate more unhealthy plant choices, those who ate the largest amount of had a 6% greater chance of developing dementia, according to the study.

“We found that adopting a plant-based diet, even starting at an older age, and refraining from low-quality plant-based diets were associated with a lower risk of Alzheimer’s and other dementias,” said lead author Song-Yi Park, an associate professor of population sciences at the University of Hawaii’s Cancer Center.

“Our findings highlight that it is important not only to follow a plant-based diet, but also to ensure that the diet is of high quality,” Park said in a statement.

Wider benefits of a plant-based diet

Beyond the brain, prior research has shown eating a healthy plant-based diet was associated with up to a 68% lower risk for diabetes, cardiovascular disease, and metabolic risk factors such as high blood pressure. Consuming an unhealthier plant-based diet, however, was associated with up to a 63% higher risk.

When it comes to the heart, studies show limiting red meat and eating whole grains, legumes, and a variety of colorful fruits and veggies can lower cholesterol and the risk of cardiovascular disease.

The risk of type 2 diabetes was cut by 24% in people who ate the most whole grains, fresh fruits and vegetables, and limited their intake of unhealthy plant and animal foods. The diet also lowered body mass index and waist circumference.

Eating a healthy plant diet has also been linked to longer life — for both people and the planet. A 2023 report by the EAT-Lancet Commission, composed of leading scientists from 16 countries, found closely following a planet-friendly diet of mostly fruits, vegetables and whole grains reduces the risk of premature death by nearly one-third in people, while also dramatically cutting the release of greenhouse gases devastating the planet.

“For every major cause of death we looked at, there was a lower risk in people with better adherence to the planetary health diet,” coauthor Dr. Walter Willett, professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health in Boston, told CNN in a prior interview.

“The findings show just how linked human and planetary health are. Eating healthfully boosts environmental sustainability — which in turn is essential for the health and well-being of every person on Earth,” Willett said.

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