Unclear mechanism
During follow-up, 670 participants developed disabling dementia.
Total fiber intake was “inversely and linearly” associated with risk of incident dementia, the authors reported, with each successive quartile associated with a lower risk compared to the lowest quartile (P for trend = .03).
The association remained after adjustment for potential factors that might affect dementia onset, such as body mass index, systolic blood pressure, antihypertensive medication use, serum total cholesterol, cholesterol-lowering medication, and diabetes (P for trend = .05).
“The inverse association was more evident for soluble fiber intake and was confined to dementia without a history of stroke,” the authors reported. Moreover, potatoes, not vegetables or fruits, showed a similar association.
“The mechanisms are currently unknown but might involve the interactions that take place between the gut and the brain,” Dr. Yamagishi said in a release.
“One possibility is that soluble fiber regulates the composition of gut bacteria. This composition may affect neuroinflammation, which plays a role in the onset of dementia,” he suggested. “It’s also possible that dietary fiber may reduce other risk factors for dementia, such as body weight, blood pressure, lipids, and glucose levels.”
The authors noted several limitations. For example, they did not distinguish between Alzheimer’s and non-Alzheimer’s dementia. Moreover, they classified dietary habits on the basis of a single survey, and participants’ dietary patterns might have changed over the study period.
In addition, Dr. Yamagishi noted, it is “important to confirm the association in other populations.”
Balance is key
In an interview, Uma Naidoo, MD, director of nutritional and lifestyle psychiatry, Massachusetts General Hospital, and nutrition educator at Harvard Medical School, both in Boston, said the study “adds to the growing pool of evidence suggesting that a diet rich in colorful, plant-based foods can benefit our neurological and psychiatric health, especially as we age.”
Dr. Naidoo, a chef and the author of “This Is Your Brain on Food,” who was not involved in the study, continued, “In nutritional psychiatry, balance is key and therefore consuming a well-rounded diet including ample amounts of fiber – particularly from sources like steel-cut oats, beans, lentils, and numerous other fruits and vegetables – can be part of a healthy lifestyle and prevention against cognitive decline in later years.
“While the study authors admit to limitations within the study, in my opinion, eating healthier has so many mental and physical health benefits that it’s a nutritional psychiatry no-brainer,” she added.
The study was partly supported by Health and Labour Science Research Grants for Dementia from the Ministry of Health, Labour and Welfare of Japan; JSPS Kakenhi; FULLHAP; and the Osaka University International Joint Research Promotion Programme with University College London. The authors and Dr. Naidoo report no relevant financial relationships.
A version of this article first appeared on Medscape.com.