Fibre — The Fourth Pillar
Fibre — The Fourth Pillar
Fibre is technically a carbohydrate — but it behaves nothing like the carbohydrates we normally think about. Most carbs are broken down into glucose early in digestion. Fibre is not. Instead, it reaches your gut bacteria intact. They ferment it and turn it into short-chain fatty acids — powerful signalling molecules that help stabilise hunger, improve gut lining barrier integrity, and keep blood-sugar responses smoother.
This is why, for practical nutrition, fibre deserves to sit alongside protein, fats and carbohydrates as a fourth pillar in its own right.
Different types of fibre
There isn’t just “one fibre”. Different fibres behave differently in the body — and feed different microbes.
| Type | Where it appears | How it behaves |
|---|---|---|
| Soluble fibre | fruit, oats, barley, beans | dissolves in water, slows digestion, smooths glucose rise |
| Insoluble fibre | vegetables, skins, whole grains | adds bulk, keeps things moving |
| Resistant starch | beans, lentils, cooked-and-cooled potatoes / rice / pasta | resists digestion and acts like fibre — hugely beneficial for gut bacteria |
There are hundreds of species of bacteria in your gut — and each has its own set of enzymes. Fibre isn’t broken down in one single step, and different species cooperate to complete the process. So variety matters — not megadosing one isolated fibre type.
Fibre is often found in the skins of plants (apples, potatoes, carrots) — but it’s not only there. The soft flesh of fruit, beans, whole grains, seeds and nuts also contain multiple fibre structures. Fibre is built into the plant itself.
What about animal foods?
Animals don’t make fibre. Fibre is a plant structure.
Fibre is also considered a type of prebiotic — meaning it feeds beneficial bacteria in your gut. Polyphenols (found in berries, herbs, olives, cacao, tea, spices) are also prebiotic — they aren’t fibre, but gut bacteria can convert them into beneficial compounds too. This is another reason why plant diversity matters.
Fibre + polyphenols together support a healthy gut microbiome — they are partners, not competitors.
Why this matters for metabolic health
The short-chain fatty acids produced from fibre fermentation help:
- reduce blood sugar spikes
- calm chronic low-grade inflammation
- support gut barrier integrity
- reduce appetite and stabilise hunger signals
This is one of the mechanisms behind the 30 Plants a Week approach: fibre diversity feeds microbial diversity — and that diversity supports steadier, calmer metabolism.
How fibre flattens sugar spikes
Fibre reduces glucose spikes in three ways at once:
- it slows how fast food leaves the stomach due to signalling when bulky food is present
- it physically slows down how quickly digestive enzymes can reach and break down starch
- and when your microbes ferment fibre, they produce short-chain fatty acids that help your body handle glucose more effectively
So fibre doesn’t just “help digestion”.
It actively changes the speed, timing and quality of how carbohydrates are absorbed — which is why meals higher in fibre tend to produce gentler, steadier blood sugar responses. They also help reduce overall calorie intake by naturally reducing hunger.