There is increasing evidence that the type of fibre we eat contributes directly to the health of our gut.
Our gut holds the key to digestive health and there is no system in our body that is not affected by our gut, including our metabolic, musculoskeletal and neurological systems.
Fermentable fibre, namely inulin and beta-glucan, are dietary constituents found in certain wholefood sources that we can’t break down, so they travel through most of our digestive tract relatively unscathed. They help feed the microbe community, most of which is located in the distal part of our colon, which also happens to house our immune cells (around 70 per cent).
There is a complex interaction between our immune system and our gut, and though these microbes hold the key to our overall health, what we eat (and how we live) largely determines the health of the gut microbiome.
Certain fruits, vegetables, legumes and whole grains contain fermentable fibre, but to clarify, when I’m talking about whole grains, I’m not talking about cereals or breads made from whole grains as they have been processed to an extent that they don’t need additional human intervention to digest them further. I’m talking about whole oats and barley, which are pretty much the only true whole grains readily found in the modern food supply.
There’s a delicate balance between our gut microbiota and our immune system. Living in close proximity are these two systems which for a long time in microbiology were thought not to get along. Bacteria are one of the things our immune system protects us from, and in our gut is a cell lining that protects the immune system from bacteria. They are in constant communication as to how to keep harmony between the two communities.
These conversations are signalled to immune cells around the body and influence our resilience against common life stressors (such as work, family, lack of sleep) and the risk of conditions, such as respiratory infections, and even the progression of more chronic health conditions. So the relationship between our gut microbiome and our immune system is a lot larger than just the gut itself.
Short chain fatty acids
Indigestible fermentable fibres are used by bacteria in the gut to stabilise blood glucose levels, reduce blood triglycerides, produce “good” bacteria for our gut and to produce short chain fatty acids (SCFA). These SCFA provide signals to the immune cells to help regulate their function and are actually “bacterial waste” — waste our bodies need to absorb to regulate a number of different aspects of our biology.
Though there are many functions of SCFA, an important one is their role in increasing the number of T-regulatory cells which help with regulating immune response. An inappropriate and overactive immune response is the key biological action underpinning almost all chronic and autoimmune disease, including allergies, asthma and type 1 and 2 diabetes.
In the absence of the fermentable fibre, the gut bacteria are forced to feed on the mucus layer that helps protect our immune system from our gut in our large intestine. The breakdown of this “mucin” reduces the gap between the microbes and epithelial cells, creating a situation where the harmony between the gut bacteria and our immune cells is compromised.
The immune cells react to this gradual encroaching on their “space” and the gut microbes also get more aggressive due to their requirement for fuel, creating an inflammatory environment. Furthermore, the SCFA are required by the cells of the gut to produce the mucin in the first place, so there really is a double whammy when we don’t get our fermentable fibre.
If we look back in time, it’s clear from the evidence that we used to eat a lot more dietary fibre than we do now. Traditional communities eat up to 150g of fibre a day, whereas the average New Zealander consumes around 18-23g per day. Though I’m not suggesting that we aim for the amount our evolutionary ancestors ate, definitely making moves to include more fermentable fibre is key to our overall health.
The modern diet is built around foods that are processed, packaged and refined and low in these fermentable fibres. These foods are quickly digested in the upper section of the digestive tract, leaving little for our gut bacteria to feed off, and these dietary patterns essentially starve the bacteria of the fuel necessary to support health.
How to increase fermentable fibre
Though there are specific fibre products (such as inulin) you can include in your diet, legumes, fruits and vegetables in general contribute to our fermentable fibre intake. The richest sources of beta glucans are whole oats, barley and mushrooms. Kumara, leeks, jerusalem artichokes, bananas, onions and garlic contain inulin, as does asparagus.
There is no specific recommendation for these fermentable fibres, however regularly including foods from this list is ideal to ensure a frequent and consistent intake. Nadia Lim's jerusalem artichoke soup will certainly get you on your way.
For people who suffer from gas production, bloating and cramping when including these fermentable fibres, working with a practitioner on a gradual increase in intake while reducing overall dietary stress is recommended.
Related: Ray McVinnie makes sauerkraut
Mikki Willidenis a registered nutritionist and lecturer at AUT University, where she lectures in public health nutrition and sports nutrition at the School of Sport and Recreation. ReadBite articles from Mikki or visit mikkiwilliden.com for more.