People with a family history of Alzheimer’s can reduce their risk with diet changes, scientists say. Here’s how to start.

A big, new long-term study suggests that sticking to a healthy diet can cut your risk of developing Alzheimer’s, especially if you were born with genetic risk factors.

The study, from nutrition and genetics researchers at Harvard Medical School, compared the genes and diets of 16,497 women and 9,828 men across the US, over three decades. The study tracked cognitive changes in the participants, keeping tabs on what people ate and to what extent they followed a typically Mediterranean diet pattern, filled with fresh vegetables, olive oil, nuts, fish, and legumes.

Many studies have shown that a Mediterranean-style diet, filled with key nutrients in ingredients like fatty fish, beans, and nuts, can help reduce dementia risk and promote brain health. This is the first time, however, that a study has shown that people at higher genetic risk of developing Alzheimer’s derive even more cognitive benefits from such a diet.

In this study, the 420 people with two copies of the APOE4 gene variant — the gene most closely associated with Alzheimer’s risk — were able to cut their risk of developing dementia by 35% by adhering to a diet rich in omega-3s, fiber, and leafy greens.

“This is not something reported by previous studies or something we would be sure to expect,” first study author Yuxi Liu told Business Insider.

A protective “synergy” between foods like olive oil and leafy greens

There isn’t one secret ingredient in the Mediterranean diet that appears to be protective. You can’t replicate the brain health benefits with supplements. Instead, researchers talk about a certain beneficial “synergy” inherent in Mediterranean meals.

“The way we absorb nutrients from food is different,” assistant nutrition professor Puja Agarwal, who works at the Rush University Alzheimer’s Disease Center, and who was not involved in this study, told Business Insider. “The way it goes to our gut and along with fiber content and different other aspects of diet makes it absorb in a certain way, which is not exactly similar to a supplement.”

Researchers aren’t exactly sure what is driving the brain benefits, but they suspect healthy fat plays a role (maybe it’s the presence of all that olive oil?) and some component of carotenoids (chemicals in brightly colored fruits and vegetables) that may affect pathways in the brains of APOE4/4 carriers, preventing dementia.

About 25% of us have one copy of the APOE4 gene variant linked to Alzheimer’s (and 6,317 study participants did), a trait which roughly doubles to triples the risk of developing the disease.

Having two copies of APOE4, one from your mother and one from your father, is rarer, affecting only about 2% to 3% of the global population. This increases the risk of developing Alzheimer’s further, upping a person’s odds by more than eightfold — putting people at a roughly 60% chance of developing the disease in their lifetime. Actor Chris Hemsworth has been open about his own “4/4” status.

This new study is especially valuable to researchers, Agarwal said, because there is barely any solid research on what — if anything — 4/4 people can do to protect their brains from deteriorating. That’s in part because we don’t have much long-term data on people at risk of Alzheimer’s, making it hard to draw firm conclusions between genetics, diet, and disease outcomes.

“The study brings in another layer to our discussion,” Agarwal said. “Each nutrient has its own pathway and these pathways might not be exactly the same for individuals with different genetic predispositions.”

The research was funded in large part by government grants from the National Institutes of Health, which were canceled earlier this year.

What you can do: eat more veggies and healthy fats

Everyone can benefit from prioritizing whole grains instead of refined white ones, plus leafy greens, berries, and healthy fats from sources like olive oil, walnuts, and fish.

Agarwal said it’s too early to design a science-based, anti-Alzheimer’s diet that’s specifically tailored to APOE4/4, but small tweaks can make a difference.

“If you can’t drastically change your diet because it’s difficult to change what you’re eating, try to take simple small steps,” she said. “Incorporate more greens in your diet, throw in more berries and fruits in your salads.” Toss some whole-grain quinoa on there.

In the future, Liu hopes that we’ll be able to tailor people’s diets more precisely to work in tandem with their genetics, in what is becoming a booming field of precision medicine.

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