Dietary fiber and its links to dementia

March 25, 2022

The World Health Organization (WHO) estimates that by 2030, 1 in 6 people in the world will be aged 60 years or over1. With this silver tsunami looming large across the entire world, so does the incidence of dementia. Over 55 million people around the world is estimated to be living with dementia in 2020, and this number is likely to double in the next 20 years2. Are there simple ways that we can take to prevent dementia from setting in and developing?  A recent Japanese study may have found an association between fibers and dementia. Read on more!

Evidence of fiber use and dementia incidence

You may have known of the importance of fibers more for their gut health and management of constipation. Several studies have also shown that a diet high in fiber can also help to decrease incidences of Type 2 diabetes and cardiovascular diseases3. However, did you know that an increased amount of fiber in our diet may be able to decrease the risk of developing dementia?

One study in Japan4 has shown that a high intake of fiber, especially soluble fiber, is linked to a lower risk of developing disabling dementia. In this Japanese study, investigators conducted a dietary survey to over 3,700 healthy adults and collected data on what and how much was eaten during the 24 hours before the interview. These adults were subsequently followed through for the next 20 years to confirm incident dementia, including disabling dementia.

It was found that total fiber intake was ‘inversely and linearly associated’ with risk of incident dementia. This meant that a higher fiber intake was associated with a lower risk of developing dementia. The association remained even after the study adjusted for potential factors that might affect dementia onset, such as body mass index, blood pressure, antihypertensive medication us, serum total cholesterol, cholesterol-lowering medication, and diabetes.

One point to note is that this association was confined to dementia without a history of stroke. The study also found that this relationship was more evident for soluble fiber intake, and similar association was shown only for potatoes and not vegetables or fruits.

The authors did note several limitations of the study, which included the fact that the dietary habits may have changed over the course of the 20 years. Also, the type of dementia was not distinguished between Alzheimer's and non-Alzheimer's dementia.

How does it work?

Although the actual mechanism about how this result occurs is currently unknown, the authors of the study have discussed several possibilities to this result. Firstly, the intake of fiber has been linked with beneficial effects on several cardiovascular parameters, including blood pressure, lipid levels, and blood glucose5. Consequently, this may have led to a potential decrease in the risk of developing dementia, particularly vascular-type dementia.

Another theory hypothesized by the authors is via the alteration of the gut microbiology by the soluble fibers. The composition of intestinal bacteria was found to be associated with prevalence of dementia6. Also, a diet high in soluble fibers has been shown to improved neuroinflammationin animal studies, via the regulation of gut bacteria7. This interaction between the brain and the intestinal environment (termed as ‘brain-gut interaction’) could potentially explain the results of this study.

What are fibers, and what are soluble fibers?

Fiber is classified under the category of carbohydrate which is an essential nutrient. It is a product that is naturally present in plants. Generally, most carbohydrates are broken down into simple sugar molecules by the body. However, dietary fibers are unable to be broken down by the human body, which makes it unable to be absorbed by the body. These undigested carbohydrates are then fermented by the gut bacteria, producing short-chain fatty acids (SCFA), which have multiple benefits in keeping the colon healthy8.

There are 2 types of fibers8:

  • Insoluble fibers – this type of fiber does not dissolve readily in fluids. It adds bulk to faecal content and aids in constipation. This type of fiber is generally found in vegetables, wholegrain products, brown rice, and pasta.
  • Soluble fibers – this type of fiber dissolves readily in liquid. Apart from being fermented to form SCFAs, they also help to increase faecal bulk, soften the stool to aid in constipation. It is generally found in fruits, dried beans, and peas.


As per every type of nutrients, moderation and balance is key. Much as such soluble dietary fibers can show benefits across many physiological functions and disease states such as dementia, taking the many different types of nutrients in moderation is still the key to having a well-balanced and healthy lifestyle.


  1. World Health Organization (WHO). Ageing and Health. 2021 Oct. Available on:
  2. Alzheimer’s Disease International. Dementia Statistics. Available on:
  3. De Munter J.S.L. et al. Whole Grain, Bran, and Germ Intake and Risk of Type 2 Diabetes: A Prospective Cohort Study and Systematic Review. PLoS Med. 2007;4:e261.
  4. Kazumasa Yamagishi et al. Dietary fiber intake and risk of incident disabling dementia: the Circulatory Risk in Communities Study. Nutritional Neuroscience. 2022. Available on:
  5. Reynolds A, Mann J, Cummings J, et al. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. Lancet. 2019;393(10170):434–45.
  6. Saji N, Hisada T, Tsuduki T, et al. Proportional changes in the gut microbiome: a risk factor for cardiovascular disease and dementia? Hypertens Res. 2019;42(7):1090–1.
  7. Matt SM, Allen JM, Lawson MA, et al. Butyrate and dietary soluble fiber improve neuroinflammation associated with aging in mice. Front Immunol. 2018;9(1832).
  8. Fibrosol. Fiber. Available on: