Fibre: The Nutrient Most People Underestimate

What Fibre Actually Is — and Isn't

Fibre often gets lumped in with other carbohydrates and promptly forgotten. Yet it behaves entirely differently from sugars or starches: the human body lacks the enzymes needed to break most fibre down into glucose, so it travels through the digestive tract largely intact. That journey, it turns out, does quite a lot of useful work.

All dietary fibre comes from plants — you won't find it in meat, fish, dairy, or eggs. Grains, vegetables, fruits, legumes, nuts, and seeds are the primary sources in the typical US diet. Because fibre is a carbohydrate that isn't digested and absorbed the same way other carbs are, it contributes minimal calories while still influencing how the rest of your meal is processed.

You can check a food's fibre content on its Nutrition Facts panel — it appears under Total Carbohydrate. For a broader walkthrough of that label, see our guide to reading a nutrition label.

“Dietary fibre is one of the most important nutrients for long-term health, yet it remains one of the most consistently under-consumed. Shifting even modestly toward more plant-based whole foods can have meaningful effects on fibre intake.”

— Walter Willett, Professor of Epidemiology and Nutrition, Harvard T.H. Chan School of Public Health

Soluble vs. Insoluble: Two Types, Two Roles

Dietary fibre is commonly divided into two categories, and understanding the difference helps clarify why both matter.

Soluble fibre dissolves in water to form a thick, gel-like material in the gut. This gel slows digestion, which can moderate the rate at which glucose enters the bloodstream and may help lower LDL cholesterol levels over time. Oats, barley, apples, citrus fruits, beans, and flaxseed are well-known soluble fibre sources.

Insoluble fibre does not dissolve in water. It adds bulk and texture to stool and speeds the passage of material through the intestines, supporting regularity. Whole wheat, bran, most vegetables, and the skins of many fruits are rich in insoluble fibre.

Most whole plant foods contain both types in varying proportions, which is one reason nutrition researchers generally point to whole-food sources as preferable to isolated supplements. For a plain-language reference on fibre and other nutrition terms, visit our nutritional glossary.

Why the Fibre Gap Matters

National dietary surveys consistently show that Americans fall well short of recommended fibre intake — a shortfall sometimes called the "fibre gap." This matters because fibre is associated, in a substantial body of research, with outcomes ranging from digestive health to blood sugar regulation and cardiovascular markers. For more on those broader connections, our companion piece why fibre matters more than most people realise goes deeper.

The gap is largely a result of dietary patterns heavy in refined grains, processed snacks, and animal products — all naturally low in fibre — and light on the whole grains, legumes, and produce where fibre is concentrated. Ultra-processed foods often strip away fibre during manufacturing, even when the original ingredient contained it.

It's also worth noting what fibre isn't: it isn't a cure, and it isn't a substitute for professional medical guidance. If you have a digestive condition or chronic health concern, speak with a qualified healthcare provider before making significant dietary changes.

This article is for general informational and educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for guidance on your individual health needs.