Fibre is a true multitasker for health but is often underestimated and underprioritized. The fibre in your leafy greens, beans and porridge is quietly pulling more weight than almost any other nutrient: it feeds your gut microbes, supports immunity, helps keep blood sugar steady, and may even play a role in minimising microplastics. Here are our favourite fibre facts that may just blow your mind.   

Fibre is a Carbohydrate But Has Zero Calories.  

Not all carbohydrates are created equal and fibre is one of the clearest examples of this. Technically, fibre is a carbohydrate and composed of long chains of sugar molecules called polysaccharides. But unlike starches or sugars, humans lack the enzymes in the small intestine to break fibre down into absorbable sugars. As a result, most insoluble fibre contributes effectively zero net calories, with soluble fibres providing only a small number of calories.  

That doesn’t mean fibre is useless, quite the opposite. As it passes through the digestive tract largely intact, it adds bulk, modulates transit time, and becomes food for beneficial gut microbes, who breakdown fibre through fermentation of it into short-chain fatty acids (SCFAs). Extensive reviews show that fibre supports digestive health, improves metabolic markers, supports immunity, and helps regulate energy balance. (1)  

Modelling studies also help explain how fibre resists digestion: its water-holding capacity and viscosity slow down the movement of food through the digestive tract. This also alters enzymatic access to digestible carbohydrates, reducing the rate (or even extent) of absorption in the small intestine. (2) 

In practical terms, this means that while starchy or sugary carbs can raise blood glucose and supply energy, fibre behaves differently. It provides structure, supports gut health, and mitigates the glycaemic impact of a meal all without adding digestible calories. In other words, fibre is a carb you can’t “burn,” but that your body deeply benefits from. 

Your Gut Microbes Eat Fibre Before You Do

Whilst humans can’t digest many types of dietary fibre, our gut bacteria thrive on them. Fermentation in the colon produces the SCFAs acetate, propionate and butyrate (3), which are vital metabolites for whole-body health.  

Butyrate, for instance, is the preferred fuel source for colonocytes (the cells lining the colon), supporting gut barrier integrity, regulating cell proliferation, and helping to prevent inflammation and DNA damage. (4) 

When it comes to immunity, these short-chain fatty acids don’t just stay in the gut, they send signals that influence the entire body. By interacting with receptors on our cells, they help “dial down” excessive inflammation, keeping the immune system balanced rather than overactive. They even influence how certain genes are expressed, encouraging the production of protective immune cells (like regulatory T-cells) that keep our defences strong but measured. (5) 

While you can’t digest fibre, your gut microbes do and in doing so, they manufacture molecules that nourish your colon, reinforce your gut barrier, tune your immune system and help keep inflammation in check. 

There are Different Types of Fibre Superheroes 

Soluble fibre is the smooth operator. It dissolves partially in water, forming a gel-like substance in your gut. This slows digestion, which helps steady your blood sugar after meals and even lowers LDL (“bad”) cholesterol.  (6) 

Insoluble fibre is more like the scrub brush or loofah. It doesn’t dissolve in water, but it adds bulk to your stool, helps soften it, and speeds up how quickly things move through your digestive tract, in other words, it keeps you regular.  

Resistant starch is interested because whilst technically a starch, it behaves like a fibre (think cooked and cooled potatoes, overnight oats, and green bananas). It too “resists” digestion in the small intestine and arrives in the large intestine largely intact, where it becomes food for the gut microbes. Fermented down there, it helps produce SCFAs, supports gut health, and may even improve insulin sensitivity.  (7)