When the saying “roughage keeps you regular” was coined it reflected fiber’s ability to prevent or relieve constipation.

Soon doctors were touting the benefits of dietary fiber for everything from helping maintain a healthy weight and lowering the risk of diabetes to reducing the risk of heart disease and some forms of cancer.

Now, a first-of-its-kind study from Japan has extended these remarkable health benefits to the brain.

Let’s take a closer look at how fiber can help you preserve your memory.

Scientists from the University of Tsukuba, led by Professor Kazumasa Yamagishi, had previously conducted a small study focused solely on beans, which are high in fiber. They found the more beans consumed, the lower the risk of dementia.

This interesting finding led them to extend their analysis to other fiber-rich foods.

Fiber Reduces Dementia Risk by Up to 25 Percent 

For the new research project, the researchers gathered data from an ongoing study involving 3,739 men and women between the ages of 40 and 64.

They asked each participant to recall what they ate over the previous 24 hours. Then they followed up with these folks as many as twenty years later when they discovered that 670 of them had been diagnosed with dementia.

The researchers calculated the quantity of fiber in each person’s diet and divided the amounts into four quarters of intake. After taking various influencing factors for dementia into account they found dietary fiber intake was inversely associated with the risk of dementia.

For example, compared to those in the lowest quarter of fiber intake, those in the second lowest quarter had a 17 percent reduced risk of dementia. This risk reduction rose to 19 percent for the next highest quarter of fiber intake. The folks in the top quarter of fiber intake saw a risk reduction of 25 percent compared to those in the lowest quarter.

Researchers also found the association between fiber intake and dementia risk reduction was stronger for soluble rather than insoluble fiber.

Soluble Fiber vs. Insoluble Fiber 

The soluble form of fiber dissolves in water and forms a gel-like material. This form feeds healthy gut bacteria and is responsible for most of fiber’s health benefits. While many sources of fiber contain both forms, soluble fiber is found in higher amounts in oats, lentils, peas, beans, Brussels sprouts, avocados, apples, citrus fruits, and carrots.

The insoluble form of fiber helps propel material through the digestive tract and forms softer, bulkier stools. This is the type that “keeps you regular.” Good sources include whole grain products, nuts, corn, grapes, berries, and the peel of apples and pears.

Potential Mechanisms For the Benefits of Fiber in the Brain 

Prof. Yamagishi shared his thoughts on why fiber might be good for the brain specifically.

“The mechanisms are currently unknown but might involve the interactions that take place between the gut and the brain. 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.

“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 work is still at an early stage, and it’s important to confirm the association in other populations.”

My Takeaway 

This is the first prospective study – the type in which participants are enrolled before they develop the condition – to find this fiber-dementia link and the professor is right to be cautious about these findings.

As he and his colleagues point out in their paper, published in the journal Nutritional Neuroscience in February, there are limitations to their research. These include relying on participants’ recollection on what they ate on a single day, the possibility that their dietary habits might have changed over the two decades follow up, and the lack of any socioeconomic information.

Although “eat more fiber” is a positive general health message, we’ll have to wait for larger, more robust studies, to see whether fiber really is good for the brain. That being said, there’s no question that fiber is good for the body. Eating a fiber-rich diet is, without a doubt, a good idea.


  1. https://www.tsukuba.ac.jp/en/research-news/20220210140000.html
  2. https://www.tandfonline.com/doi/full/10.1080/1028415X.2022.2027592 

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