It is not a supplement that we hear of often. In my opinion, it is well-hidden from the public eye, yet, inulin has been researched for over 20 years as a type of soluble fibre that is beneficial for our health.
Most recently, inulin made headlines in the nutrition world by being associated with a lower risk of developing dementia and Alzheimer’s. The study (https://www.tandfonline.com/doi/full/10.1080/1028415X.2022.2027592) involving 3,700 Japanese population assessed dietary patterns from 1985 to 1999 and showed that consumption of soluble fibre lowered the risk of both Alzheimer’s and disabling dementia, without the history of stroke.
Fibre is a buzz word in the world of human nutrition, and has been a buzz word since I could remember. When I was a kid my grandfather was recommended by his doctor to eat fibre in the form of prunes to prevent constipation. And even though many of us hear we should be including more fibre in our diet daily, the general association of the benefits of fibre on our health is simplified to those of my grandfather’s. And it is a pity!
Our hunter-gatherer ancestors ate approximately 150g of fibre daily. They foraged on plants, dug out plant roots, ate flower petals and devoured on berries when in season. They also realised that plants were their only type of medicine, and treatments were made in the form of plant infusions, vapours and tinctures. Plants are indeed living pharmacies that dispense natural substances with medicinal powers. Many pharmaceutical drugs have their origins in plants.
Consumption of fibre by general population in the Western world is at its all-time low right now. Compared to our hunter-gatherers, the typical Brit eats a paltry 8-13g of fibre daily. The most recent National Nutrition and Diet Survey (https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/943114/NDNS_UK_Y9-11_report.pdf) showed that in the adult population aged 19-64 only 9% of people met the government recommended intake of 30g of fibre daily. In the elderly (over 65 years old) 6% met the government recommendation. In children aged 4 to 10, 14% are regularly meeting the fibre intake. The lowest intake is among teenagers - aged 11 to 18 - where only 4% meet the fibre recommendation.
What is in fibre that is important for us that extends beyond the benefits of regular bowel motions? Vegetables and fruit are our only source of phytonutrients (phyto meaning plants), a group of chemicals essential to health, which protect us from inflammation, cancers, cardiovascular diseases, infections, auto-immune diseases and a long list of chronic inflammatory conditions.
There are two types of fibre: soluble and insoluble. Soluble fibre (found in fruit, beans, oats, barley, rice, potatoes) is fermented in our large intestine by beneficial bifidobacteria to produce short-chain fatty acids (SCFAs). Soluble fibres are considered prebiotics - they are food for the microorganisms in our gut. Soluble fibre helps bind bile acids, regulates cholesterol levels and blood sugar levels, helps to maintain good pH balance in the intestines.
Insoluble fibre (found in bran, vegetables, whole grains) is poorly digested by our gut, and thus facilitates gut motility - the way food can move through the digestive tract, regulating elimination.
Our large intestine contains the majority of the microbiota - the microorganisms that inhabit the digestive tract. Here, bifidobacteria, a beneficial type of microorganism, ferment fibres from the plants we eat, in the process short-chain fatty acids (SCFAs) are produced. There are 4 main types of SCFAs: butyrate, pripionate, acetate and valerate. SCFAs are small organic monocarboxylic acids with a chain length of up to six carbon atoms, and are the main product of fermentation of indigestible polysaccharides.
The disruption of the gut microbiota - dysbiosis, on the other hand, has been associated with the development and progression of behavioural and neurologic diseases - depression, anxiety, autistic spectrum disorder, Parkinson’s. (https://www.frontiersin.org/articles/10.3389/fendo.2020.00025/full)
Several studies have previously shown that dietary soluble fibre can improve neuroinflammation, which is often associated with the onset of Alzheimer’s. The gut-brain axis plays an important role in the accumulation of amyloid protein plaques as seen in Alzheimer’s patients. (https://academic.oup.com/nutritionreviews/article/74/10/624/2349955)
The communication between the gut and the brain is centred within the ENS - the enteric nervous system (or as it is often called "the second brain”). The ENS is the nervous system that runs through our digestive system. ENS has about 100 million neurons that are found in sheaths of tissues lining the entire digestive tract. ENS is directly connected to the brain via the vagus nerve. Thus the communication between the central nervous system (CNS) in response to the information we receive from the environment and the ENS is constant and bidirectional. The secretion of bile and digestive enzymes, digestive juices, the production of gut bacteria and also gut motility and the ability of the gut to create defence mechanisms (immunity) are deeply dependent on the functions of the gut-brain axis.
There is mounting evidence that shows that several types of bacteria in our gut can excrete mixtures of amyloid and lipopolysaccharides (LPSs) substances that create undesirable physiological responses in our immune system that cause ill effect in our brain. Changes in the gut bacteria activate pro-inflammatory cytokines and increase intestinal permeability, which often leads to insulin resistance and type 2 diabetes. LPSs, for example, are directly linked to inflammatory conditions that result in insulin resistance and diabetes 2. It is for this reason that researchers often stress that type 2 diabetes, metabolic syndrome diseases and Alzheimer’s are deeply connected. (https://academic.oup.com/nutritionreviews/article/74/10/624/2349955)
“Increasing evidence suggests that clumping of proteins with prion-like behavior might be a phenomenon shared by many of the major CNS diseases, like AD, Parkinson’s disease, Huntington’s disease, and amyotrophic lateral sclerosis.” - cite the researchers.
The microorganisms that control the gut–brain axis are mainly bacteria belonging to about 1000 different species; there are also bacteriophage particles, viruses, fungi, and archaea. There are six predominant bacterial families (or phyla) in our gut: Bacterodietes, Firmicutes, Actinobacteria Proteobacteria, Verrucomicrobia and Euryarchaeota.
The study of the role of fibre on dementia risks in the Japanese population showed that the number of Bacteroides species (mainly beneficial bacteria types) was lower among patients with dementia than among those without it. (https://www.tandfonline.com/doi/full/10.1080/1028415X.2022.2027592)
As we age, and our dietary patterns change, the concentrations of short-chain fatty acids (SCFAs) dwindle, with some researchers saying that the intake of dietary fibre is as much as 40% lower in the elderly than the recommended intake.
In addition, with ageing there’s often a disruption in the communication and balance between the brain and the defence mechanisms of the immune system. Microglia - the type of macrophages that are specific to our brain - are the immune cells that are on constant guard against pathogens - begin to change to pro-inflammatory types in ageing people. Thus the body cannot rely on the same defensive mechanisms as in younger age. Byturate, as one of the main beneficial SCFAs, has been shown to exert beneficial effects on microglia and receptor signaling, which is demonstrated in this the new study from the Japanese population.
A diet rich in soluble high-fiber foods enhances the abundance of the Bacteroides species. The people in the study consuming a variety of foods containing soluble fibre - potatoes, rice, vegetables and fruit, and sodium had a positive outcome on the risks of developing disabling dementia or Alzheimer’s. Interestingly, the researchers commented that the amount and variety of insoluble fibre did not have an effect on the risks of dementia and Alzheimer’s.
Inulin is a type of soluble fibre that increases levels of butyrate in the gut. It is a group of non-digestible carbohydrates called fructans, which we can get from such dietary sources as green bananas, Jerusalem artichokes, leeks, chicory, asparagus. It is also available in the form of a supplement. According to Liz Lipsky, taking 5g of inulin regularly can drastically improve the health of the gut and also ensue all the positive effects of the SCFAs, including the new evidence of protection against disabling dementia and Alzheimer’s.
I personally do not eat enough chicory, Jerusalem artichokes and leeks, thus I aim to get inulin supplement 3-4 times a week. Would you try it too?