Dr Alan Barclay
The low down on dietary fibre
We hear lots about dietary fibre these days – in particular how good it is for us and how we all need to eat more. In this first of a two-part series, I explore what it is, why we think it is good for us, and why most of us need to eat more.
What fibre actually is The current definition of dietary fibre is much the same around the globe. Australia and New Zealand’s food regulator FSANZ says: “dietary fibre means that fraction of the edible part of plants or their extracts, or synthetic analogues that are resistant to the digestion and absorption in the small intestine, usually with complete or partial fermentation in the large intestine … and includes polysaccharides, oligosaccharides and lignins.” This basically means that dietary fibres come mostly (but not exclusively) from plants and that they are the poorly digested portions that pass through into the large intestine (bowel) and provide much of the bulk in our stools (along with water and bacteria, amongst a few other things).
There are a number of ways of classifying the different types of fibre. One of the most popular systems is whether they are soluble in water or not:
- Water soluble fibres include gums (e.g. agar), fructans (e.g. inulin), mucilages (e.g. psyllium) and pectins. They are found in a range of foods including fruits, vegetables, legumes (beans, peas and lentils) and some grains (oats and barley)
- Water insoluble fibres include cellulose, hemicellulose and lignins. They are mostly found in vegetables, wheat and other wholegrains, nuts and seeds.
Why we think fibre is good for us “Fibres promote one or more of the following beneficial physiological effects – laxation; reduction in blood cholesterol; modulation of blood glucose” says the second part of the FSANZ definition. Soluble dietary fibre may help reduce blood cholesterol levels and modulate blood glucose levels – but whether it does so or not depends in part on the degree of food processing and of course how much you eat. High cholesterol and blood glucose levels are risk factors for heart and other blood vessel diseases and type 2 diabetes and there is evidence that high fibre diets can indeed reduce the risk of heart disease, but perhaps surprisingly, there is little evidence that high fibre diets by themselves reduce the risk of type 2 diabetes. Insoluble dietary fibre primarily helps with laxation, which in turn may decrease the risk of constipation, haemorrhoids and colo-rectal (bowel) cancer.
Why most of us need to eat more Australia’s nutrition recommendations advise that women consume 25 grams of total fibre each day and men 30 grams each day. Based on the most recent nutrition survey, Australian intake is not far under the target amounts and way ahead of the US and UK with women eating 21 grams of fibre a day and men 27 grams. In the USA, women consume just over 14 grams a day and men just under 18 grams. In the UK, women consume 12.8 grams a day and men 14.8 grams a day. But, here’s what has been dubbed the Australian fibre paradox. Despite the relatively high average fibre intakes, Australians have some of the highest rates in the world of bowel cancer – ahead of the UK and US.
In part 2 (March), I’ll show how we can all incorporate more fibre into our diets in an enjoyable way, and talk about whether or not high fibre foods are low GI as many people think.
The GI Symbol, making healthy low GI choices easy choices
For more information about the GI Symbol Program
Dr Alan W Barclay, PhD
Chief Scientific Officer
Glycemic Index Foundation (Ltd)
Phone: +61 (0)2 9785 1037
Mob: +61 (0)416 111 046
Fax: +61 (0)2 9785 1037