Dietary Fibre

Dietary fibre is an important part of the human diet. It is a major determinant of gut health and plays a large role in protecting against bowel cancer. Although it provides virtually no nutrients or energy, it is crucial for fermentation in the large intestine, leading to microbial growth. This is known to form larger stools and shorten the amount of time it takes for the waste to pass through the intestines. Most dietary fibres are polysaccharides, strings of monosaccharides linked together. Lignins, cutins and tannins are some of the non-polysaccharides that are classed as dietary fibre.

The main health benefit of fibre is faecal bulk. Soluble fibre ferments in the gut, creating short-chain fatty acids along with bulky stools able to easily clear out potential carcinogens. As soluble fibre meets water and forms into a gel, the muscles along the digestive tract find it easier to push the food along until it is passed out as waste. Lack of fibre in the diet contributes to constipation and it can affect up to 30% of the population, especially pregnant women and older people.

Currently, Australian adults are not meeting the recommended amount of fibre in their diets, with an estimated intake of only 20-25 grams. Though the gap has been closing in recent years, the high incidence of bowel cancer in Australia means we should not rest on our laurels.

So what exactly IS this magical thing you call fibre?

Soluble fibre is so named because the fibres will dissolve in water. Soluble fibre is glutinous; it is fermentable in the large intestine (e.g. pectins, some hemicellulose and psyllium). Soluble fire is essential for diabetics as it slows down glucose absorption in the blood, preventing a flood of insulin release.

Insoluble fibre is, conversely, fibre that will not dissolve in water. It is opposite to soluble fibre in that it doesn’t form into a gel in water and is not fermentable. The insoluble fibre is what makes up the bulk of the faecal matter and promotes regular bowel movements. It is the major property of fruit and vegetable skins, whole grains, brown rice and legumes.

Starches are long chains of glucose molecules that are broken down by the body into glucose. They boost the growth of good bacteria in the gut, which in turn enhances the benefits of soluble fibre and improves large bowel function.

Phytic Acid is technically not classed as a dietary fibre but because is it often found in the same foods as both soluble and insoluble fibre. Phytic acid may be responsible for binding with minerals to prevent their absorption.

Further important health benefits of dietary fibre include:

• Low blood cholesterol
• Weight control
• Slower glucose absorption
• Reduced risk of cardiovascular disease
• Cancer prevention- particularly colorectal (bowel) cancer.

Lower your cancer risk

Colorectal cancer makes up approximately 9% of all cancer diagnoses worldwide and is the fourth most common cause of cancer death. It is the second most common cancer to be developed by women and the third most common for men. A large percentage (almost 60%!) of cases are in developed countries, with Australia and New Zealand having some of the highest rates of incidence in the world.

The Aune et al. meta-analysis of 19 quality studies found that higher intakes of fibre and wholegrains are directly associated with a decrease in bowel cancer risk. They found that for every extra 10g/day of fibre consumed, the risk of bowel cancer reduced by 10%!

The National Health and Medical Research Council (NHMRC) recommends that high-fibre grain foods make up 1/3 of Australians’ diet. Adults are recommended to consume between 25-30 grams of dietary fibre per day, whilst very young children should consume at least 14 grams.

There is a mountain of evidence supporting the addition of extra fibre in the diet, but be aware that lifting the level of fibre too quickly may lead to a bit of bloating and flatulence! Foods have different levels of soluble and insoluble fibre, and the levels change according to how they are prepared. 

To increase your fibre and resistant starch intake:

• Snack on nuts
• Substitute white bread with wholemeal or multi-grain bread
• Use brown rice instead of white
• Eat whole-wheat pasta, and serve ‘al dente’ 
• Include oats or bran in your breakfast routine
• Leave the skin on your fruits and vegetables
• Add lentils or beans to meat dishes
• Try to eat at least five serves of vegetables and 2 serves of fruits each day
• Cooked and cooled potato is very high in resistant starch

Fibre intakes over 40 grams a day can be linked with malabsorption of some minerals. The key is to eat a varied diet each day, don't stress about junk foods in moderation and enjoy life!

If you have any concerns about your bowel health, see your G.P.