, new research shows.
Investigators administered a dietary survey to 3,700 healthy adults at midlife and then followed them for up to 20 years. They found that participants who consumed the most fiber had approximately a 25% lower risk of developing dementia in later life.
“This study showed that people with a high intake of dietary fiber, especially soluble fiber, have a lower risk of dementia,” study investigator Kazumasa Yamagishi, MD, PhD, professor, department of public health medicine, faculty of medicine and health, Services Research and Development Center, University of Tsukuba, Japan, said in an interview.
“There are still many unknowns about the causes of dementia, and it is not appropriate to determine causality based on the results of a single cohort study. However, the results of this study can be said to be one of the findings that will lead to the prevention of dementia,” Dr. Yamagishi said.
The study was published online Feb. 6 in Nutritional Neuroscience.
Brain-gut interaction has recently received attention for its potential involvement in the development of dementia. “The concept of brain-gut interaction emerged from the idea that the central nervous system communicates bidirectionally with the gastrointestinal tract, suggesting that the gut microbiome may influence brain plasticity and cognitive function,” the authors wrote.
A diet high in soluble fiber attenuates neuroinflammation in mouse models. Other animal studies have suggested that insoluble fiber might also have a beneficial effect on the microbiome.
The researchers wanted to see whether dietary fiber intake – especially soluble fiber – is associated with a reduced risk of dementia. They also investigated whether there was any difference between dementia in patients with vs. without a history of stroke.
In a previous study, these same researchers reported an inverse association between eating beans, which are high in fiber, and risk of disabling dementia. In the current study, the researchers extended the analyses to dietary fiber intake of total, soluble, and insoluble fibers, as well as other fiber-containing foods, such potatoes, vegetables, and fruits. However, they distinguished potatoes from other vegetables because the composition of starch in potatoes differs.
“Dietary fiber is a nutrient found in grains, potatoes, vegetables, and fruits and is known to affect intestinal bacteria,” Dr. Yamagishi said. “Recently, some experimental studies have shown that intestinal bacteria may be involved in cognitive functions as well as diseases of the digestive tract. However, there have been no studies that have actually examined the relationship between dietary fiber intake and the subsequent risk of dementia in large numbers of general people.”
The researchers turned to participants in the Circulatory Risk in Communities Study (CIRCS), an ongoing dynamic community cohort study involving five communities in Japan. The current study focused on communities where disabling dementia surveillance is conducted.
Participants (n = 3,739) ranged in age from 40 to 64 years (mean age, 51 years) at the time they completed the 24-hour dietary recall survey, and they participated in annual health checkups from 1985 to 1999. Potential risk factors for disabling dementia were measured at the time the dietary surveys were conducted. Participants were then followed for a median of 19.7 years (1999-2020) to confirm incident, disabling dementia.
“Disabling dementia” was defined as dementia that required care under the National Long-Term Care Insurance System and was further categorized on the basis of having a history or not having a history of stroke.
The researchers divided participants into quartiles, based on the amount of total, soluble, and insoluble intake reported in their surveys. They found that men tended to consume less total fiber compared to women.