Dementia is a progressive neurocognitive condition that is ranked fifth among the most common causes of death in Americans 65 years of age and older. The incidence of dementia is increasing in the US due to an aging population and additional factors. Some known risk factors for dementia include age and history of certain systemic diseases, including diabetes mellitus and cardiovascular disease. The research community has also explored the potential connection between the gut-brain axis and dementia.

Dietary fiber is digested in the large intestine, and it is believed to influence the gut microbiome. Certain agents in the microbiome may influence brain health; one study reported a lower amount of Bacteroides species in individuals with dementia compared to healthy individuals. High-fiber diets have been associated with increases in certain health-promoting gut microbes, including Bacteroides and others that may influence short-chain fatty acid production and neuroinflammation.

A long-term community study by Yamagishi and colleagues was recently published in the journal of Nutritional Neuroscience that investigated the link between dietary fiber intake and the risk of incidence for disabling dementia. Between the years of 1985 and 1999, more than 3,700 primarily healthy Japanese adults 40 to 64 years of age were surveyed for nutritional intake, including dietary fiber. A follow-up of the same study participants occurred between 1999 and 2020 that assessed the incidence of disabling dementia among them.

Potential risk factors were considered during the study. Blood pressure measurements were among the data collected in the trial. Patient history was recorded from each study participants, including alcohol and smoking status, tobacco use, history of stroke, medication use, serum glucose, and total cholesterol.

Study results indicated an inverse association between the intake of dietary fiber, particularly soluble fiber, and the incidence of disabling dementia in this population. The authors of the study discussed the potential mechanisms for this correlation. Some proposed reasons were the role of fiber in supporting cardiovascular health, healthy lipid metabolism, normal blood pressure, and the risk of cardiovascular or metabolic conditions. The authors also discuss the potential for fiber to modulate the composition of the gut microbiome.

Limitations to the study included the nature of the dietary surveys. Dietary intake in the study was only collected as a 24-hour recall. This methodology may not be fully capturing the usual nutrient intake of the participants.

The health-supportive role of dietary fiber in the human body is still being elucidated in modern scientific research. It is suggested by the study authored by Yamagishi and colleagues that dietary fiber, although shown to support many aspects of human health, may also support healthy aging and long-term cognitive health.

By Colleen Ambrose, ND, MAT