- Over 55 million people around the world are estimated to be living with dementia, with Alzheimer's Disease (AD) being the most common type.
- Although the exact causes of AD have yet to be fully established, amyloid and tau proteins are found to accumulate in the brain of patients with AD. Neuroinflammation is also often a key element in AD.
- Health of our gut microbiota is associated with AD. Harmful bacteria may worsen neuroinflammation, while metabolites from beneficial gut bacteria may help protect against it.
- Prebiotics could be used to enhance and regulate the health of the gut microbiota, thereby lowering the risk of developing AD.
Over 55 million people around the world are estimated to be living with dementia in 2020. This number is likely to double every 20 years, reaching a total of 78 million by the year 2030 [1]. The most common type of dementia is Alzheimer’s Disease (AD). We have discussed how dietary fiber may have effects on dementia based on a Japanese study done recently which found that a high intake of dietary soluble fiber is linked to a lower risk of developing disabling dementia [2]. Most prebiotics are dietary fibers. However, not all dietary fibers are prebiotics. Read on to find out more about the effects of prebiotics and gut microbiota on dementia and Alzheimer’s disease.
Our gut consists of trillions of such microorganisms including bacteria, viruses, fungi and protozoa species. This composition of microorganisms residing in our gut is collectively termed gut microbiota, which is unique to everyone. It varies due to several factors, such as environmental, lifestyle, dietary habits, and consumption of medications such as antibiotics [3].
This innate set of gut microbiota (the set that we are born with) is thought to be the most optimum for oneself. This optimum composition deteriorates as we age. Along with poorer modern-day diets lacking in prebiotics (i.e., food for the beneficial gut bacteria) as well as increased use of medications, the composition and amount of good gut bacteria decrease even faster.
Prebiotics are defined by the International Scientific Association for Probiotics and Prebiotics (ISAPP) as a substrate that is selectively utilized by host microorganisms conferring a health benefit [4]. In loose terms, prebiotics are food for the beneficial gut bacteria in a process called fermentation. This feeding process produces metabolites such as short-chain fatty acids (SCFAs) which confer health benefits to us. One such health benefit could be healthy aging.
Although the exact causes of AD have yet to be fully established, it has been found that various types of proteins (e.g., amyloid and tau proteins) accumulate in the brains of patients with AD [5]. Neuroinflammation is also a key element in the accumulation of amyloid hence the progression of AD [6].
The health of our gut microbiota is associated with AD. The gut microbiota and the brain communicate bi-directionally, and this interaction has been termed the gut-brain axis [7]. Dysbiosis, which refers to an altered gut microbiota, has been associated with various neurodegenerative diseases including AD. Reduction in microbial diversity has been observed in patients with AD as compared to patients without [8].
Harmful gut bacteria may even produce amyloid peptides, which can enter the bloodstream due to increased gut permeability. These peptides can then cross the blood-brain barrier and accumulate amyloid in the brain, further exacerbating AD [9]. Metabolites produced from harmful bacteria can also worsen neuroinflammation in the brain, while metabolites (such as SCFAs) produced from beneficial gut bacteria may help protect against AD by inhibiting the aggregation of amyloid peptides and maintaining cognitive functions [9,10].
Prebiotics are food selectively utilized by beneficial gut bacteria. By taking prebiotics, we improve the health of our gut microbiota by allowing the beneficial bacteria to grow and proliferate, at the same time crowding out the harmful ones. This may help to ameliorate the risk factors of AD such as gut permeability, amyloid peptides, and systemic inflammation [9].
There is currently no cure for AD. Current evidence points to the importance of the gut microbiota as a modulator of neurodegenerative diseases such as AD. The gut microbiota serves as a promising therapeutic target for the prevention and treatment of AD. Prebiotics could potentially be used to enhance and regulate the health of the gut microbiota, thereby lowering the risks of neurodegenerative diseases.
Dietary Fiber and Its Links To Dementia
Prebiotic: Gut Microbiota, Gut Health, and Beyond
- Over 55 million people around the world are estimated to be living with dementia in 2020, and this number is likely to double in the next 20 years.
- Soluble dietary fibers are unable to be broken down by the human body and are then fermented by the gut bacteria, producing short-chain fatty acids (SCFAs).
- One study in Japan has shown that a high intake of fiber, especially soluble fiber, is linked to a lower risk of developing disabling dementia.
- The authors of the study have discussed several possibilities for this result: beneficial effects on several cardiovascular parameters and improved neuroinflammation via the effects on the gut microbiota.
The World Health Organization (WHO) estimates that by 2030, 1 in 6 people in the world will be aged 60 years or over [1]. With this silver tsunami looming large across the entire world, so does the incidence of dementia. Over 55 million people around the world are estimated to be living with dementia in 2020, and this number is likely to double in the next 20 years [2]. 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 fiber and dementia. Read on more.
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 diseases [3]. 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 Japan [4] 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.
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 glucose [5]. 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 dementia [6]. Also, a diet high in soluble fibers has been shown to improved neuroinflammation in animal studies, via the regulation of gut bacteria [7]. This interaction between the brain and the intestinal environment (termed as ‘gut-brain interaction’) could potentially explain the results of this study.
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 (SCFAs), which have multiple benefits in keeping the colon healthy [8].
There are 2 types of fibers [8]:
- Insoluble fibers – this type of fiber does not dissolve readily in fluids. It adds bulk to fecal 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 fecal 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.
Gut Microbiota and Its Implications in Diabetes and Blood Sugar
Gut-Brain-Immune Axis: An Introduction
What is Dietary Fiber & Why is it Important?
What is the Gut Microbiota?