By Gabrielle Streeter, BENS MDietSt (UQ)

Fibre is most commonly acknowledged for its contribution to faecal formation; however, fibre has many unrecognised health benefits that go beyond the bowel.

Various studies observing the implications of high fibre diets have found evidence to support that increased consumption may improve lipid profiles and blood glucose control, and reduce the risk of obesity along with lifestyle-related illnesses including type 2 diabetes and cardiovascular diseases, and other particular gastrointestinal disorders.  Evidence is also building in terms of the importance of fibre in cancer prevention and the protective action of fibre intake in bowel health.

What is Fibre?

Fibre is a nutrient that is too often underused and not well understood. It can be defined as any part of food that is not digested in the small intestine that moves essentially unchanged to the colon where it can undergo partial or complete bacterial fermentation. This metabolic process results in the production of short chain fatty acids (SCFA), which play an important role in promoting intestinal health. There are three main types of fibre: soluble, insoluble and resistant starch. All have different roles and contribute to health in ways that extend beyond faecal formation.

Soluble Fibre

As the name suggests, soluble fibre dissolves in water, forming a thick gel in the intestines. It helps to prevent constipation, but also aids in slowing digestion and making you feel fuller for longer. This in turn can help to lower LDL (bad) and total cholesterol that can lead to heart disease, as well as stabilise blood glucose levels and increase insulin sensitivity. This fermentable fibre also acts as a prebiotic supporting health-promoting bacteria of the colon. This type of fibre is readily metabolised by bacteria, releasing SCFAs that act as growth factors for a healthy gastrointestinal system and also elicit seemingly protective actions against colon cancer. It is high in foods such as fruits and vegetables, dried beans, lentils and oats.

Insoluble Fibre

Insoluble fibre is responsible for adding bulk to your stools, which helps to keep your digestive tract moving and regular. Similarly to soluble fibre, it helps to give you that fuller feeling; but, unlike soluble fibre, it is not easily metabolised by bacteria. Foods high in this type of fibre include whole grain breads and cereals, the outer skins of fruit and vegetables, nuts and seeds, along with cooked lentils, kidney beans and chickpeas.

Resistant Starch

For many years it was thought that the only food components to enter the bowel undigested were insoluble and soluble fibre, and that all starches contained in foods were completely broken down in the small intestine. However, opposing evidence found that a significant portion of starch resisted digestion in the small intestine and moved into the bowel where it behaved like fibre in the sense that it could be fermented to produce SCFAs, eliciting similar health benefits to soluble fibre. Because of its nature it was titled resistant starch (RS). There are four types of RS that vary depending on the resistant nature of the molecule. Further research is needed to determine if type of RS influences physiological function. Foods high in RS include under-ripe bananas, cooked and cooled potatoes and rice, slightly undercooked pasta (‘al dente’) and products such as Hi-Maize that can be added to foods to increase fibre content.

Our Fibre Requirements:

National Health Medical Research Council (NHMRC) sets fibre requirements as will all other nutrients based on the preventing deficiency states. The recommendation for fibre intake is:

• Adequate Intake (AI) = 25g/day for women, 30g/day for men for adequate laxation and gastrointestinal function.

The NHMRC also recognises that fibres plays a role in preventing or reducing the burden of chronic disease and thus provides a suggested dietary target for fibre as well.

• Suggested Dietary Target (SDT) = 28g/day for women, 38g/day for men based on evidence for intake that may help prevent or lower the risk of chronic diseases such as diabetes.

Tips for Increasing Fibre Intake

• Include wholegrain breads, cereals, pasta and rice in your diet
• Aim for 5 serves of vegetables and 2 pieces of fruit each day
• Include pulses & legumes such as beans and lentils in your diet
• Snack on nuts and seeds
• Ensure you drink at least 2L of water every day to avoid constipation associated with high fibre intake
• Increase fibre intake gradually. Sudden increases can lead to bloating, flatulence and stomach cramps

Fibre is not a cure for all our disease woes; however, it does play a key role in helping maintain our overall health and wellbeing. These benefits go beyond bowel health and extend into cardiovascular health, blood glucose control and reducing cancer risk.