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High Fibre Diets: What are they and do they work?

May 16, 2018

First things first...What is fibre?


Well the sciency, hard to understand definition...as defined by the Food Standards Australia and New Zealand (FSANZ) is:

‘Dietary fibre means that fraction of the edible parts of plants or their extracts, or synthetic analogues, that are resistant to digestion and absorption in the small intestine, usually with complete or partial fermentation in the large intestine. Dietary fibre includes polysaccharides, oligosaccharides and lignins, and promotes one or more of the following beneficial physiological effects:

(i) laxation (makes you go to the loo)

(ii) reduction in blood cholesterol

(iii) modulation of blood glucose’. ¹



Let’s break that down.

In simpler terms, dietary fibre is a part of the plants we eat that our body is unable to break down and digest. Instead, these parts are stewed for a while (fermented) in the large intestine to produce what are called short chain fatty acids (SCFA). These short chain fatty acids are a source of energy for the cells that line our gut.²  Fibre is also sometimes known as roughage, or bulk.


Just so you don’t have to read the word poo a heap of times, the word ‘stool’ = poo over the next few paragraphs. Aren't we nice? Don't we take care of you?




There are two types of fibre: insoluble and soluble, as well as something called resistant starch, which we’ll get to in a moment.


Soluble fibre, like the name suggests, is soluble in water. It makes a gel like consistency and helps to soften and slow the passing of stools (so helps with diarrhoea!). It can also grab hold of (bind) cholesterol and sugar, and help to slow/prevent the absorption/reabsorption of them. This means that soluble fibre may help lower your blood cholesterol levels, and slow the absorption of sugar into the blood.³ ⁴  It can be found in fruit, vegetables, oats, barley, and legumes.


Insoluble fibre attracts water to the stool and adds bulk. It helps make the stool big enough to be able to pass easily. It can be found in foods containing whole grains and in the skins of fruits and vegetables.


There is also a third substrate called ‘resistant starch’. This has not always been considered ‘dietary fibre’, but is very like fibre and is also helpful to our gut. It is a starchy part of food (starchy = long, complex chains of sugar molecules like in potatoes or the inside of rice) that isn’t fully digested in our small intestine. So, when it reaches the large intestine it is something that the bacteria in our gut can ferment to make those short chain fatty acids we mentioned earlier.


So now that we know what fibre is, what is classified as a high fibre diet?

There is no recommended dietary intake (RDI) for fibre, but there is an adequate intake (AI). This is a value that is estimated by looking at how much regular, healthy Australian and New Zealand folks eat. For women, 19-70+ years, it is 25g per day. For men, 19-70+ years, it is 30g per day.⁵ Many of us do not meet this day to day. As there is no upper limit set for how much fibre is safe to eat, a high fibre diet may be classified as dietary fibre intake greater than the recommended adequate intake.



Some great sources of fibre include:

  • Apples

  • Figs

  • Banana

  • Raspberries

  • Mango

  • Avocado

  • Wholegrains (think oats, barley, rye, corn, brown rice, quinoa)

  • Lentils

  • Beans e.g. black beans, baked beans

  • Broccoli

  • Carrots

  • Potato/Sweet Potato

  • Nuts and Seeds (think chia, flax, linseed, almonds)

  • Psyllium Husk, Oat Bran (these are powders that are great for sprinkling over things or using in cooking)

                                                   Definitely not what Homer eats. Ever.



Lastly, is a high fibre diet actually good for you?


The bottom line is, as with so many things in the health area, it depends!


So far, the research about high fibre diets has indicated that it:

  • Can lower blood cholesterol measures. ¹ ³ ⁴

  • May assist in the relief of diverticular disease symptoms⁶  (but not necessarily during a flare-up). The diet may be more effective in combinations with synbiotics (tablet with pre and probiotics in them) for those with uncomplicated diverticular disease experiencing symptoms.⁷

  • May help to reduce risk factors present in metabolic syndrome when combined with a healthy diet.⁴

  • Can assist with regular, healthy bowel motions.¹ ² 

    • Constipation

    • Diarrhoea

  • Increase the variety and abundance of healthy bacteria in our gut and therefore, overall large intestinal health.²


So there you have it. Fibre is pretty amazing!


As so many of us have allergies or intolerances, it can be hard to get an adequate amount of all types of fibre in your diet, especially when whole grains have to be cut out. One of our writers finds it helpful to keep a stash of fibre capsules handy, for the times when she can’t get enough fibre through food naturally. Please see your local dietitian who can help you find sources of fibre that will give you the most benefit, without exacerbating any symptoms you may have.


Naomi Fitzpatrick

(University of Queensland, Student Dietitian)



ABOUT THE AUTHOR: Naomi Fitzpatrick is a current Masters of Dietetics student from the University of Queensland. Born and bred on the Sunshine Coast she has always loved the outdoors, cooking and well…food! She believes everyone deserves the opportunity and knowledge to build their best lifestyle and way of eating that works for them. She is very lucky to have no issues with food herself, but this doesn’t make her any less passionate about helping others. She wants to help others build the knowledge to make their own informed choices, no matter their food issue or allergy! If you like her stuff, check her out on Instagram and Facebook through The Allied Health Project



1. National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand. National Health and Medical Research Council; 2017 p. 40-43. Retrieved From: https://www.nhmrc.gov.au/_files_nhmrc/file/your_health/healthy/nutrition/17599_nhmrc_nrv_update-dietary_intakes_0.pdf


2. Simpson H, Campbell B. Review article: dietary fibre-microbiota interactions. Alimentary Pharmacology & Therapeutics [Internet]. 2015 [cited 15 November 2017];42(2):158-179. Available from: http://onlinelibrary.wiley.com.ezproxy.library.uq.edu.au/doi/10.1111/apt.13248/full


3. Samaan R. Dietary fiber for the prevention of cardiovascular disease. Academic Press; 2017.Retrieved From: https://www-sciencedirect-com.ezproxy.library.uq.edu.au/science/book/9780128051306


4. Pal S, Khossousi A, Binns C, Dhaliwal S, Ellis V. The effect of a fibre supplement compared to a healthy diet on body composition, lipids, glucose, insulin and other metabolic syndrome risk factors in overweight and obese individuals. British Journal of Nutrition [Internet]. 2010;105(01):90-100. Available from: https://www-cambridge-org.ezproxy.library.uq.edu.au/core/journals/british-journal-of-nutrition/article/effect-of-a-fibre-supplement-compared-to-a-healthy-diet-on-body-composition-lipids-glucose-insulin-and-other-metabolic-syndrome-risk-factors-in-overweight-and-obese-individuals/DDE90317EE5D477C1E0594B6E2B1AA79


5. Dietary Fibre | Nutrient Reference Values [Internet]. Nrv.gov.au. 2017 [cited 15 November 2017]. Available from: https://www.nrv.gov.au/nutrients/dietary-fibre


6. Ünlü C, Daniels L, Vrouenraets B, Boermeester M. A systematic review of high-fibre dietary therapy in diverticular disease. International Journal of Colorectal Disease [Internet]. 2011;27(4):419-427. Available from: https://link.springer.com/article/10.1007%2Fs00384-011-1308-3


7. Lahner E. High-fibre diet and Lactobacillus paracasei B21060in symptomatic uncomplicated diverticular disease. World Journal of Gastroenterology [Internet]. 2012 [cited 15 November 2017];18(41):5918. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3491599/


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