Eating to prevent dementia — what Japan's Hisayama Study and Mediterranean and MIND diet research have shown

Summary — The link between diet and dementia has been studied in many countries. In the Hisayama Study (2013), in which Kyushu University has followed residents of Hisayama town in Fukuoka for decades, a dietary pattern high in soy and tofu, vegetables, seaweed and milk and dairy and relatively low in rice was associated with lower dementia risk. Finland's FINGER trial (2015) reported better-maintained cognition in a group combining diet, exercise, cognitive training and vascular risk management. By contrast, a US randomised trial that changed diet alone, the MIND diet trial (2023), found no clear difference from the control group.

The Hisayama Study: Japanese dietary patterns and dementia

The Hisayama Study is a landmark community cohort study that Kyushu University has run since 1961 among residents of Hisayama town in Fukuoka Prefecture. It is known for very high participation and detailed follow-up extending to autopsy. The team surveyed the diets of about 1,000 residents aged 60 and over and followed them for around 15 years for dementia.

People whose dietary pattern was high in soybeans and soy products, green, yellow and other vegetables, seaweed, and milk and dairy, with a relatively lower share of rice, had a lower risk of dementia, including Alzheimer's and vascular dementia. The study is significant for adding important data on Asian dietary patterns to research that had been largely Western. As an observational study, however, it cannot establish that diet itself prevented dementia; other lifestyle habits of people eating this way may also have played a part.

The Mediterranean and MIND diets

In Western countries, the Mediterranean diet — centred on vegetables, fruit, whole grains, legumes, fish and olive oil — attracted attention for cardiovascular health and for its association with maintaining cognition. A team at Rush University in the United States proposed the 'MIND diet', combining the Mediterranean and DASH (hypertension-prevention) diets with emphasis on green leafy vegetables and berries, and reported in an observational study (2015) that people who followed it closely developed Alzheimer's disease less often.

However, when the same team randomised about 600 overweight older adults to the MIND diet or a control diet for three years (2023), cognitive scores improved in both groups and the difference between them was not statistically significant. Because the control group also received mild calorie restriction and counselling, one interpretation is that both groups improved their lifestyles. The result shows that associations seen in observational studies may not be confirmed in randomised trials.

The FINGER trial: the whole lifestyle, not diet alone

In Finland's FINGER trial, about 1,200 people aged 60–77 at risk of dementia were randomised; one group received nutritional counselling, an exercise programme, cognitive training and management of vascular risks such as blood pressure and glucose for two years. That group's overall cognitive score was better maintained than the control group's. The trial is widely cited as evidence for a 'multidomain approach', and similar studies are now under way in several countries, including Japan.

Dietary principles you can follow now

• A balanced diet with frequent vegetables, soy and tofu, seaweed and fish
• Less sugary drinks, processed food and salt to help manage blood pressure and glucose
• Avoiding excessive alcohol, and in later life watching for protein shortage and weight loss

The World Health Organization's 2019 guidelines also recommend a healthy, balanced diet as one way to reduce the risk of cognitive decline. There is no evidence that any single food prevents dementia; managing the overall dietary pattern together with exercise and social activity is what matters.

A caution about supplements

Many supplements and health foods claim to improve memory, but most have not been shown in randomised studies to prevent dementia. They may also interact with medicines, so it is best to consult the medical team before using them.

Frequently asked questions

Q. Do coffee or green tea help prevent dementia?
Observational studies in several countries, including Japan, report less cognitive decline in people who drink moderate amounts of green tea or coffee, but prevention has not been confirmed in randomised studies. It is best understood as something to enjoy in moderation without disturbing sleep.

Q. Do supplements such as omega-3 help?
An association between eating fish often and cognition has been reported in observational studies, but randomised trials of supplements have not consistently shown improved cognition. Getting nutrients from food comes first.

Q. Is a little alcohol fine?
International reports list excessive drinking as a dementia risk factor. Starting to drink to prevent dementia is not recommended.

Q. Is changing diet worthwhile in old age?
In later life, shortages of protein and energy and weight loss can themselves raise the risk of frailty and cognitive decline, so eating enough is important.

How to look up clinical trial information

Ongoing and completed clinical trials can be checked on public registries. ClinicalTrials.gov, run by the U.S. National Library of Medicine, and jRCT, run by Japan's Ministry of Health, Labour and Welfare, publish each study's purpose, eligibility criteria, intervention, outcomes, institutions and status. Results are later published as journal papers, and the reference links below this article lead to the original information. It is also worth knowing that interventions not publicly registered are difficult to verify from outside, in both design and results.

The above summarises published papers and public-agency materials. University and institute names are given to identify research sources, not to introduce or recommend any medical institution. Please discuss a diet suited to you with your medical team or a nutrition professional.

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