Scientists from the University of Tsukuba in Japan have found that eating a diet rich in fiber may help lower the risk of developing dementia.
The study, led by Kazumasa Yamagishi and colleagues, was published in the journal Nutritional Neuroscience.
Dietary fiber, also known as roughage, is the indigestible part of plant foods. It is well known for its health benefits, including lowering the risk of heart disease and type 2 diabetes.
Fiber is mainly found in vegetables, fruits, whole grains, and legumes.
There are two main types of dietary fiber: soluble and insoluble. Both are important for good health and most plant foods contain a mix of the two.
Soluble fiber absorbs water like a sponge and forms a gel-like substance in the gut. This helps slow digestion, supports healthy bowel movements, and plays a key role in lowering levels of LDL, or “bad,” cholesterol. Soluble fiber includes compounds such as pectins, gums, and mucilage, which are found in the cells of many plants.
Insoluble fiber, on the other hand, does not absorb water. Instead, it adds bulk to stool and helps move waste more quickly through the digestive system.
This type of fiber includes substances such as cellulose, hemicellulose, and lignin, which make up the structural parts of plant cell walls. Its main role is to prevent constipation and related problems, including hemorrhoids.
While scientists have long suspected that dietary fiber may help protect against dementia, clear and long-term evidence has been limited. In this study, the researchers set out to examine whether higher fiber intake was linked to a lower risk of developing dementia.
The team analyzed data from 3,739 Japanese adults aged 40 to 64 who had completed detailed dietary surveys between 1985 and 1999. Fiber intake was estimated using a 24-hour dietary recall method. The researchers then followed these participants for more than 20 years, tracking dementia diagnoses between 1999 and 2020.
Over the course of the follow-up period, 670 people developed dementia. The results showed that higher dietary fiber intake was associated with a lower risk of developing the condition. This protective effect was strongest for soluble fiber and was mainly seen in cases of dementia that occurred without a prior history of stroke, suggesting that fiber may be particularly helpful in preventing non-vascular forms of dementia.
Interestingly, the researchers also found a similar protective link with fiber-rich foods such as potatoes, but not with vegetables or fruits. This unexpected finding suggests that the source and type of fiber may be important and deserves further investigation.
The scientists believe that one possible explanation is that soluble fiber helps regulate the balance of gut bacteria. Changes in the gut microbiome may influence inflammation in the brain, a process that is thought to play a role in the development of dementia. In addition, a high-fiber diet may reduce other known dementia risk factors, such as obesity, high blood pressure, abnormal cholesterol levels, and poor blood sugar control.
Overall, the findings suggest that including more fiber-rich foods, especially those high in soluble fiber, as part of a healthy and balanced diet could be a simple and effective way to support long-term brain health.
