Over the years, we’ve come to understand more about the gut and, in particular, about the huge collection of bacteria – the gut microbiome – that it sustains, and their role in helping to develop and maintain a healthy metabolism, a healthy brain and a healthy immune system. We now also know that a major piece in the gut health puzzle is fibre, especially a type of dietary fibre called resistant starch.
As we’ve unravelled the interactions between our gut microbiome and our immune system, we’ve learnt that this all starts at birth, when microbial colonisation of the gut occurs. This early microbiome has a role in shaping the development of a person’s immune system. Eating the right types of foods for feeding the gut microbiome during infancy has been shown to have life-long immune-system benefits.
By the age of about two-and-a-half to four years, the gut microbiome has fully developed. The make-up of the microbiome population of an individual then remains relatively stable throughout adulthood, although significant alterations can occur. There are also gradual shifts as we age. Establishing a good gut microbiome early on plays an important role in maintaining health throughout life.
An imbalance in our gut microbiome can be brought on by poor diet and lifestyle choices over the long term, including a diet low in dietary fibre and high in processed foods. It may contribute to the development of disease, including type 2 diabetes. Individual differences in the composition of our but microbiome may affect how the body reacts to some dietary components and may also predispose some people to particular diseases. Advances in analysing our microbiome may help deepen our understanding of its role in human health, and allow us to personalise diets to improve our health and wellbeing and allow us to personalise diets.
Fibre is Essential
Dietary fibre consists of a diverse group of mostly plant-based complex carbohydrates that are not digested – that is, they are not broken down by the enzymes in the upper gastrointestinal tract.
Since dietary fibres are not digested in the small intestine, they are available as a food source for the gut microbiome populations that about in the large intestine.
Of the nutrients we consume, fibre has the biggest influence on the gut microbiome. A diverse range of dietary fibres creates a diverse and more resilient gut microbiome, leading to good gut health by building an environment less favourable to the growth of potentially harmful microbes, while also enhancing the immune system and the healthy functioning of the tissues and gut barrier.
A healthy gut environment is associated with a decreased risk of a range of diseases, including bowel cancer, type 2 diabetes and obesity.
Fibres are generally classified as soluble or insoluble. Resistant starch is also important for sup- porting a healthy gut microbiome.
Since the various types of fibres vary in their capacity to promote gut health and function, the best option is to consume a wide variety of wholefoods that are as close to their natural state as possible. This ensures that a diverse range of beneficial gut microbial species can thrive and thereby promote gut health.
Soluble fibres dissolve in water to form viscous gels that slow the passage of ingested food through the upper GI tract. Soluble fibres are also rapidly fermented in the large intestine, making them a good source of fuel for your gut bacteria.
- Lower cholesterol
- Slow digestion, which helps control hunger and increases the body’s ability to absorb beneficial nutrients
- Support the growth and activity of good bacteria.
- Nuts, seeds and legumes
- Oats, barley and psyllium husk
- Fruit, ie apples, mango, pears, oranges, prunes
- Vegetables, ie Brussels sprouts, eggplant, broad beans, parsnips, onion.
Insoluble fibres, previously called roughage, account for about 70 per cent of most plant food fibre. They tend to be slowly and incompletely fermented by the gut, commonly increasing stool bulk. Some insoluble fibres are fermented, increasing beneficial bacteria.
- Attract and retain water, increasing food volume; creating a sense of fullness to control appetite
- Assist in propelling food along the GI tract
- Increase stool bulk and aid in laxation.
- Chickpeas, lentils
- Wholegrain cereals, breads and pasta
- Nuts and seeds
- Fruit, such as unpeeled pears and apples
- Vegetables, ie green beans, spinach, cabbage.
Resistant starch resists digestion in the small intestine, passing through to the large intestine, where it is used by the gut microbiome. Although resistant starch is an insoluble fibre, it is extensively fermented by the gut microbiome. It is available in starchy foods, often in small amounts, and its structure can change during food cooking and cooling.
- Encourage the growth of beneficial bacteria
- Lower cholesterol, assisting with blood glucose control.
- Legumes, ie chickpeas
- Grains, such as rye, oats and barley
- Under-ripe bananas
- Cooked and cooled starchy foods, such as potatoes, sweet potatoes, rice, pasta and beans.
FROM THE CSIRO GUT CARE GUIDE BY DR MICHAEL CONLON, PENNIE TAYLOR, DR CUONG TRAN AND MEGAN REBULI. © 2021. PUBLISHED BY MACMILLAN AUSTRALIA.