Most of us know that dietary fibre is good for our health and wellbeing. Many of the health benefits we obtain from consuming dietary fibre occurs when dietary fibres pass through to our large bowel (intestine), and are digested by the trillions of microorganisms that form our microbiome, converting the indigestible carbohydrate in to important fuels (e.g., fatty acids like butyrate), gases (e.g., hydrogen), and providing the bulk so important for laxation.
WHAT EXACTLY IS DIETARY FIBRE? The United States Food and Drug Administration recently narrowed its definition of dietary fibre to: “non-digestible soluble and insoluble carbohydrates (with 3 or more monomeric units), and lignin that are intrinsic and intact in plants” and “isolated or synthetic non-digestible carbohydrates (with 3 or more monomeric units) determined by FDA to have physiological effects that are beneficial to human health.” “such as lowering blood glucose and cholesterol levels, increasing feelings of fullness (satiety) resulting in reduced calorie [kilojoule] intake, and improving bowel function.”
To-date, the list of isolated or synthetic fibres that have been assessed and classified as fibre by the FDA includes:
- Β-glucan soluble fibre
- Psyllium husk
- Cellulose
- Guar gum
- Pectin
- Locust bean gum
- Hydroxypropylmethylcellulose
- Arabinoxylan
- Alginate
- Inulin and inulin-type fructans
- High amylose starch (resistant starch 2)
- Galactooligosaccharide
- Polydextrose
- Resistant maltodextrin/dextrin
WHAT ARE THE DIFFERENT TYPES OF FIBRES INTRINSIC TO PLANTS AND WHAT ARE THEIR FUNCTION? While we are generally advised to “eat more fibre”, there are many different types of dietary fibres that occur naturally in plant foods, and they don’t all have the same effect on our health. Here’s a summary of the intrinsic/intact fibres in our foods and their primary function:
HOW MUCH FIBRE DO WE NEED? It is generally agreed we need at least 3.3 g of fibre for every 1000kJ (240 calories) of energy we consume each day. This equates, on average, to:
- Children aged 1–3 – 14g a day
- Children aged 4–8 – 18g a day
- Boys aged 9–13 – 24g a day
- Boys aged 14–18 – 248 a day
- Girls aged 9–13 – 20g a day
- Girls aged 14–18 – 22 a day
- Men aged over 19 – 30g a day
- Women aged over 19 – 25g a day
- In the USA in 2010, people consumed an average of 2.0g per 1000kJ (240 calories), or 16g per day.
- In Australia, people consumed around 2.5g per 1000kJ (240 calories) and fibre intakes appear to be dropping, from 23.1g per day in 1995 to 22.9g in 2011/12 likely thanks to the popularity of fad diets (e.g., low fructose; gluten free; low-carbohydrate diet) that are typically lower in fibre.
Alan Barclay, PhD is a consultant dietitian and chef (Cert III). He worked for Diabetes Australia (NSW) from 1998–2014 . He is author/co-author of more than 30 scientific publications, and author/co-author of The good Carbs Cookbook (Murdoch Books), Reversing Diabetes (Murdoch Books), The Low GI Diet: Managing Type 2 Diabetes (Hachette Australia) and The Ultimate Guide to Sugars and Sweeteners (The Experiment, New York).
Contact: You can follow him on Twitter or check out his website.