Dietary Fibre: Make It More Than An Afterthought
Dietary fibre is actually classified as a type of carbohydrate. You’d be excused if you’re surprised by this, as carbs are usually thought of within the context of bread and pasta. In some circles, people choose to avoid carbs like your ex at a wedding, but by doing so may actually be skimping on their fibre intake too. Naturally, we don’t endorse this (avoiding carbs, not your ex).
For those who aren’t anti-carb, you are likely aware that consuming a combination of protein, carbohydrate and fat helps to achieve a balanced diet, while thinking about dietary fibre may be more of an afterthought.
However, in more recent times, dietary fibre’s PR has undergone a glow-up (it’s giving Belly from TSIP) and is getting more well-deserved attention. Online, we have fitness influencers promoting fibre supplements and high-fibre diets, and in the supermarket, fibre is popping up in the most random spots. It’s added to lollies, chocolate bars, biscuits and more. Japan took this to a whole other level and launched a fibre-enriched version of the popular cola drink in 2017 (you know, the red one).
What is dietary fibre?
And also, why is there corn in my poo? Allow me to explain.
Dietary fibre is the part of plant foods that cannot be digested in the small intestine, so it’s instead passed along to the large intestine. Yeah, I know the description is a bit anti-climactic, but let’s dive into it and see why this is actually pretty cool.
We know in principle that we eat food, and it comes out looking different from what was put in. That’s why our poop doesn’t resemble cake slices, steak or our late-night kebab. The body breaks down food into small, absorbable pieces in our digestive system, which are then transported to wherever they are required.
Now, for the Sherlockians among us who inspect your poop occasionally (this is normal and encouraged btw 👀), there might have been times when some parts did resemble the food we have eaten. A great example is corn kernels or seeds, which represent how different types of fibre show up differently in your poop.
The types of dietary fibre include:
1) Non-starch polysaccharides (soluble and insoluble fibre) and
2) Resistant starch
Soluble and insoluble fibre
First, let’s start with the non-starch polysaccharides. Polysaccharides are a fancy way of describing a long chain of sugar molecules (i.e., carbohydrates!). Soluble and insoluble describe how the different type of fibre behaves when it comes into contact with water and our digestive juices.
If you’re a fan of overnight oats or chia pudding, like myself, you can say a big hello to soluble fibre. Soluble fibre absorbs fluid, creating a gel-like, thick consistency we see in our chia pudding. The same thing happens in our digestive tract, with soluble fibre adding bulk to our stool by increasing the water content, which also keeps our poop soft. Another example is psyllium husk, which has the ✨magical✨ ability to either soften stool to relieve constipation or provide bulk, helping with diarrhoea.[1]
Insoluble fibre may not wow you by turning milk and chia seeds into pudding, but it certainly contains many benefits. A little rougher around the edges (literally) than the soft gel-forming soluble fibre. Insoluble fibre is found in wheat bran, whole grains, nuts and seeds, and uses its larger particles to mechanically ‘massage’ your insides (stick with me here) to stimulate water and mucous secretion, resulting in a gentle laxative effect.[2][3]
Soluble and insoluble fibres are not mutually exclusive, and both are commonly found in fruit, vegetables, nuts, seeds and cereals. For example, 100 g of oats contain 10g of fibre, which consists of two-thirds of the insoluble fibre and one-third soluble. Fibre in lentils, on the other hand, is 90% insoluble.[4] Aligning with the good old ‘eat the rainbow’ recommendation, we need to remember that there is not just one type of soluble and insoluble fibre, but all kinds of subgroups which differ in their source. Meaning, it is important to eat different kinds of fibre sources to expose your gut (and our little microbe friends living in there) to a variety of soluble and insoluble fibre.
Resistance starch
Speaking of our gut microbes! Resistant starch experiences a little bit of an identity crisis, as it behaves more like dietary fibre than digestible starch, by feeding the beneficial gut bacteria in your gut microbiome. [5, 6] As the name suggests, this is a portion of naturally occurring starch in food, which is resistant to digestion in the small intestine. It is found in starchy foods including cereals, legumes, corn, fruit and vegetables; however, one of the best sources is rice, pasta or potatoes that have been cooked and then consumed cooled. [5]
So, how much and why?
In Australia, dietary guidelines suggest an adequate intake of dietary fibre is 25 g/day and 30 g/day for adult women and men, respectively. And there is good reason to pay attention to your fibre intake, other than keeping you regular. Adequate consumption has been associated with lower risks of type 2 diabetes, cardiovascular disease, and even some types of cancers, including colorectal, breast, small intestine, and oral.[7]
The actual mechanisms remain unknown, but it is likely a combination of many different factors, including getting rid of ‘the bad stuff’ like a more efficient excretion of carcinogenic compounds, LDL cholesterol, as well as more of ‘the good stuff’ like the protective antioxidants. It’s also linked to a reduced energy intake and inflammatory markers.[7]
TLDR
If you want to ensure you’re getting enough fibre without tedious counting, there are some practical tips you can follow to make sure you are on the right track:
1) Choose wholemeal options and use nuts, seeds or fruit as crunchy and versatile toppings on your food (this works for sweet or savoury!). I love adding a seed mix or crumbed walnuts to my salads and oatmeal for extra crunch.
2) Get creative: add carrots or zucchini to your baked oats or brownies for sweet options (you will not taste them, I promise!), or add lentils to minced meat or more grated vegetables and spinach to your bolognese.
3) Romanticise your snacks! I’ve seen the most appetising and lush-looking snack plates on the socials recently, making the humble vegetable sticks the star of the show. Side of dark chocolate (would be rude note to) or cheese with grapes is highly recommended.
4) Get curious! Have a look at the nutrient panel of foods, as a lot of companies already choose to list the fibre content, which helps you make an informed decision
We work with people who have all different types of fibre considerations, including those with IBS, stomas, bowel obstructions and athletes. If you require specific and personalised dietary counselling, we want to help you!
This article was written by Melanie Bruckberger.
BSc (Biomedical Science)
Master of Human Nutrition
Currently undergoing Certificate III & IV in Fitness
TDC Intern
Whether it’s cellular processes, microorganisms, nutrition or the environment, Mel loves sharing scientific insights in a digestible way (pun intended!) and empowering people to make dietary and lifestyle-informed choices.
References
1. Stribling P, Ibrahim F. Dietary fibre definition revisited-The case of low molecular weight carbohydrates. Clinical Nutrition ESPEN. 2023;55:340-56.
2. McRorie Jr JW, McKeown NM. Understanding the physics of functional fibers in the gastrointestinal tract: an evidence-based approach to resolving enduring misconceptions about insoluble and soluble fiber. J Acad Nutr Diet. 2017;117(2):251-64.
3. Bijkerk C, Muris J, Knottnerus J, Hoes A, De Wit N. Systematic review: the role of different types of fibre in the treatment of irritable bowel syndrome. Aliment Pharmacol Ther. 2004;19(3):245-51.
4. Dhingra D, Michael M, Rajput H, Patil R. Dietary fibre in foods: a review. J Food Sci Technol. 2012;49(3):255-66.
5. Fuentes-Zaragoza E, Riquelme-Navarrete M, Sánchez-Zapata E, Pérez-Álvarez J. Resistant starch as functional ingredient: A review. Food Res Int. 2010;43(4):931-42.
6. Zealand FSAN. Australia New Zealand food standards code: Food Standards Australia New Zealand.; 2007.
7. Lattimer JM, Haub MD. Effects of dietary fiber and its components on metabolic health. Nutrients. 2010;2(12):1266-89.
