3 Reasons Why You Need Fibre + Where To Get It

Fibre is the most under-consumed nutrient in the modern diet and one of the most consequential. Average Australian adults consume approximately 2022g of dietary fibre daily, against a recommended intake of 25g for women and 38g for men. The gap represents a meaningful shortfall with real health consequences. Here's why fibre matters more than you probably think, and how to close that gap practically.

What Fibre Actually Is

Dietary fibre is a catch-all term for non-digestible carbohydrates plant components that pass through the small intestine undigested and arrive intact in the large intestine, where gut bacteria ferment them. There are two main categories:

• Soluble fibre dissolves in water to form a viscous gel. Found in oats, legumes, apples, and psyllium husk. Slows digestion, regulates blood glucose, and forms the substrate for SCFA production by gut bacteria.
• Insoluble fibre doesn't dissolve. Found in whole grains, vegetables, and nuts. Adds bulk to stool, accelerates gut transit, and reduces the time potentially harmful compounds remain in contact with the intestinal lining.

Both types are important and work via different mechanisms. A diet diverse in plant foods naturally provides both.

Reason 1: Fibre Feeds the 38 Trillion Organisms Running Your Health

Your gut microbiome contains approximately 38 trillion microbial cells comparable to the number of human cells in your body. These organisms are not passive inhabitants; they're metabolically active partners in your health, producing compounds that influence immunity, mood, metabolism, cognitive function, and inflammation.

Dietary fibre specifically prebiotic fibre is their primary food source. When beneficial gut bacteria ferment fibre, they produce short-chain fatty acids (SCFAs): butyrate, propionate, and acetate. These compounds have profound effects:

• Butyrate is the primary fuel source for colonocytes (intestinal lining cells), maintaining the gut barrier that prevents bacterial products from entering the bloodstream and triggering systemic inflammation
• Propionate travels to the liver and regulates glucose production; it also signals the release of GLP-1, the appetite-regulating hormone that GLP-1 medications mimic pharmacologically
• Acetate is the most abundant SCFA, with systemic anti-inflammatory effects and a role in lipid metabolism

Without adequate fibre, SCFA production drops. The gut barrier weakens. Systemic inflammation rises. And the microbial populations that produce these beneficial compounds decline in abundance, giving space to less beneficial species. This is the mechanistic link between low-fibre diets and the chronic diseases they're associated with.

Reason 2: Fibre Controls Blood Glucose and Reduces Diabetes Risk

Soluble fibre forms a viscous gel in the digestive tract that physically slows carbohydrate digestion and glucose absorption. This blunts post-meal blood glucose spikes reducing the insulin response required and improving overall glycaemic control. Over time, this effect translates into meaningfully better insulin sensitivity and reduced type 2 diabetes risk.

The evidence is among the most robust in nutrition science. A 2019 meta-analysis published in The Lancet commissioned by the World Health Organization to inform dietary recommendations examined data from 40 prospective studies and found that people with the highest dietary fibre intake had a 1530% lower risk of type 2 diabetes, cardiovascular disease, stroke, colorectal cancer, and all-cause mortality compared to those with the lowest fibre intake. These are substantial risk reductions from a single dietary factor.

Beta-glucan the soluble fibre from oats and barley has the strongest individual evidence, supporting an FDA-approved health claim for cholesterol reduction, and consistent evidence for blood glucose management. Three grams of beta-glucan daily (approximately a large bowl of oat porridge) produces clinically meaningful reductions in LDL cholesterol.

Reason 3: Fibre Dramatically Reduces Colorectal Cancer Risk

Colorectal cancer is Australia's second most common cancer and one where the dietary evidence for fibre is among the strongest available. The mechanisms are multiple:

• Insoluble fibre increases stool bulk and accelerates transit time, reducing the duration that potential carcinogens in the gut remain in contact with the intestinal mucosa
• Butyrate produced from fibre fermentation has direct anti-cancer effects on colorectal cells it induces apoptosis (programmed cell death) in cancer cells while sparing normal cells, and inhibits the proliferation of pre-cancerous cells
• High-fibre diets maintain a gut microbiome composition that reduces the production of secondary bile acids and other compounds with tumour-promoting activity

A comprehensive meta-analysis found that each additional 10g of fibre per day is associated with a 10% reduction in colorectal cancer risk. The effect is dose-dependent more is better within the plausible range of dietary intake.

The Best Food Sources of Fibre

Practical, high-fibre foods to prioritise:

• Legumes: The single most fibre-dense category lentils (~15g per cup cooked), chickpeas (~12g), black beans (~15g). Also provide plant protein, iron, and folate.
• Oats: ~4g per cup cooked, with the added benefit of beta-glucan for cholesterol and blood glucose management
• Avocado: ~10g per medium fruit exceptionally high for a fruit, and providing healthy fats alongside
• Broccoli and Brussels sprouts: ~45g per cup and also providing glucosinolates for the gut-health and anti-cancer benefits described above
• Chia seeds: ~10g per 2 tablespoons remarkably dense; gel-forming when soaked, which supports satiety and gut motility
• Whole grains (barley, quinoa, brown rice): 36g per serving; barley specifically provides meaningful beta-glucan
• Pears and apples (with skin): 46g each; the skin contains significantly more fibre than the flesh

Closing the Fibre Gap with Supplements

For people who eat well but still struggle to hit recommended fibre targets, fibre from greens supplements meaningfully contributes. A quality greens powder containing prebiotic fibres from diverse plant sources adds to total daily fibre intake while also providing the polyphenols that work alongside fibre to modulate the microbiome.

GRNS includes prebiotic fibre from plant sources as part of its gut health formulation contributing to daily fibre intake and feeding the beneficial bacteria that make fibre's effects possible.

Frequently Asked Questions

Can I eat too much fibre?
At very high intakes (60g+ per day), fibre can cause digestive symptoms and may impair mineral absorption by binding to minerals in the gut. This is rarely a practical concern for people eating normal food the more common issue is consuming too little. Increase fibre gradually (by 35g per week) when significantly increasing intake to allow gut bacteria time to adapt.

Is fibre from supplements as good as fibre from food?
The research on most prebiotic fibre effects is agnostic on source fibre that reaches the colon and feeds beneficial bacteria has similar effects whether it came from whole food or a supplement. Whole foods provide fibre alongside phytonutrients and food-matrix benefits that supplements don't fully replicate, so whole food is generally preferable when achievable. Supplement fibre fills the gap when whole food intake isn't sufficient.

Do I need to drink more water if I increase fibre intake?
Yes. Soluble fibre absorbs water to form its viscous gel; without adequate hydration, increasing soluble fibre can cause constipation rather than improving it. Aim for at least 2L of water daily when consuming high-fibre foods or supplements.