WTF? What The... Fibre!

Updated: Mar 30, 2020

Fibre is crucial in the prevention of many chronic disease issues, and yet the majority of Australians are not meeting fibre targets (1). Ideally men should be eating 30g and women 25g of fibre per day (2). For something so important, there seems to be so much confusion about it, where it is found in food and how it helps your health, so here we go...

What is fibre?

Fibre is a term that describes carbohydrates that are not broken or absorbed in the upper part of the gastrointestinal tract, such as the small intestine and stomach (3). Dietary fibre is categorised into different types according to sources, solubility (able to be dissolved in water), fermentability and physiological effects (4) including insoluble, soluble, resistant starch (RS) and prebiotic.

Wooden basket of fresh organic fruit and vegetables with hand reaching into it.

1. Soluble fibre

Soluble fibre dissolves in water and forms a thick gel in your digestive tract. This slows gut transit time and helps you feel fuller for longer. This gel also attracts fluid to help soften your stools, making it easier for waste to move through the bowel.

It also creates a colonic environment that supports the growth of your beneficial bacteria and influences the absorption of other nutrients that are not absorbed in the small intestine. Soluble fibre also promotes healthy levels of blood sugar and insulin, fat deposition and blood lipids such cholesterol (5).

  • Classification: beta-glucans, gums, wheat dextrins, psyllium, pectin, inulin (6) and oligosaccharides (5).

  • Where do you get soluble fibre? From Oats, oat bran, barley fruits, vegetables, seed husks, flaxseed, psyllium, dried beans, lentils and peas (7).

2. Insoluble fibre

This comes from plant based foods, namely the structural parts of plant cell walls. Insoluble fibre does not dissolve in water. Instead it adds physical bulk to your stools and helps to speed up the removal of waste from your gut, which is great for preventing constipation. Many foods rich in insoluble fibre are also high in FODMAPs*.

  • Classification: Cellulose, lignin, some pectins and some hemicelluloses (6)

  • Foods high in insoluble fibre include corn, eggplant, green beans, broccoli, spinach, kale, legumes, grapes, kiwi, strawberries, rhubarb, raspberries, pineapple, blueberries, raisins, brown rice, burghal, oat bran, rice bran, buckwheat, quinoa, peanuts, almonds, walnuts pumpkin, chia and sesame seeds (8)

3. Resistant Starch

RS escapes digestion in the small intestine, and moves through to the large intestine where it acts as food for your gut bacteria. They are classified as a prebiotic (bacteria ferments/eats these), which releases beneficial short chain fatty acids which promote a healthy colon. RS is different to FODMAPs* in that it is fermented slowly in the large intestine. It is the rapid fermentation of FODMAPs* that may cause intestinal gas which, for some causes symptoms of pain, bloating and discomfort (hello IBS and SIBO). There are four types:

  • Type 1 is not accessible by digestive enzymes: partially milled grains and legumes

  • Type 2 escapes digestion because of the nature of the food: underripe bananas

  • Type 3 is produced when foods are cooked and then cooled: potatoes, rice and pasta

  • Type 4 is a chemically modified starch (9)

Check out this great video for more information on RS.

Do you get bloated when you have high fibre fruits, vegetables, pulses and legumes? It's time we talked.

4. Prebiotics (including resistant starch)

It is worth noting that all prebiotics are fiber, but NOT all fiber is prebiotic. To classify a as a prebiotic the food must:

  1. Resists gastric acidity, enzymes, and absorption in the upper gastrointestinal tract (able to reach colon)

  2. Is fermented by the intestinal microflora,

  3. Selectively stimulates the growth and/or activity of intestinal bacteria potentially associated with health and well-being, such as bifidobacteria also lactobacilli strains.

Many FODMAP* foods are prebiotics because fructans and galacto-oligosaccharides (GOS) are prebiotic fibres.

  • Example of prebiotic foods: leeks, asparagus, chicory, Jerusalem artichokes, garlic, onions, wheat, oats (6) chickpeas, lentils, red kidney beans, baked beans, soybeans, custard apples, nectarines, white peaches, persimmon, tamarillo, watermelon, rambutan, grapefruit, pomegranate, dried fruit, cashews and pistachios (10)

So, what should you be eating?

A diet that focuses on variety is the key way to eat all of these types of fibre. If you not sure what this looks like, ask yourself if you are eating the following:

  • 5+ serves of vegetables per day (1 serve = 1 cup raw or 1/2 cup cooked)

  • 1-2 serves of fruit per day

  • Lentils, legumes and pulses most if not all days of the week

  • Opting for whole sources carbohydrates in the form of quinoa, oats and rice rather packaged cereals or refined breads

  • 1/4-1/3 cup of nuts and/or seeds most days

*FODMAPs is an acronym referring to Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols, complex names for a collection of molecules found in food (11).

If you are someone that struggles to tolerate fibre, click HERE.