Carbohydrates: Dietary Fibre (NSP)

This lesson covers dietary fibre, also known as non-starch polysaccharide (NSP), as required by AQA GCSE Food Preparation and Nutrition specification 8585 (section 3.2.1). Although dietary fibre is classified as a carbohydrate, the body cannot digest it — and that is precisely why it is so important. You will learn what fibre is, its food sources, its functions in the body, and why the UK population needs to eat more of it.

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What Is Dietary Fibre?

Dietary fibre is the term for the parts of plant foods that the human body cannot digest or absorb. It passes through the stomach, small intestine, and colon largely intact.

The scientific term used in the AQA specification is non-starch polysaccharide (NSP) — this distinguishes fibre from starch, which is a polysaccharide the body can digest.

Key Facts

• Fibre is found only in plant foods — there is no fibre in meat, fish, eggs, or dairy
• The body cannot digest fibre (we lack the enzymes to break it down)
• Despite not being digested, fibre has essential functions in the digestive system
• Fibre provides virtually no energy (though gut bacteria can ferment some fibre, producing small amounts of energy)

Exam Tip: The AQA specification uses the term NSP (non-starch polysaccharide). In the exam, you may see either "dietary fibre" or "NSP" — they mean the same thing. Use whichever term appears in the question, or use both to show your understanding.

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Types of Dietary Fibre

Dietary fibre is classified into two types based on how it behaves in water:

Type	Description	Food Sources	Function
Insoluble fibre	Does not dissolve in water. Absorbs water and swells, adding bulk to faeces.	Wholemeal bread, brown rice, bran, whole wheat pasta, vegetable skins, nuts, seeds	Adds bulk to stools, speeds up transit time through the gut, prevents constipation
Soluble fibre	Dissolves in water to form a gel-like substance.	Oats, barley, fruit (especially apples, citrus), vegetables, pulses (beans, lentils, chickpeas), flaxseeds	Slows digestion, helps lower blood cholesterol, helps regulate blood sugar levels

Both types of fibre are important, and a healthy diet should include a variety of fibre-rich foods to obtain both.

graph TD
    A["Dietary Fibre — NSP"] --> B["Insoluble Fibre"]
    A --> C["Soluble Fibre"]
    B --> B1["Does NOT dissolve in water"]
    B --> B2["Adds bulk to faeces"]
    B --> B3["Prevents constipation"]
    B --> B4["Sources: wholemeal bread, bran, brown rice, vegetable skins"]
    C --> C1["Dissolves in water — forms gel"]
    C --> C2["Lowers blood cholesterol"]
    C --> C3["Regulates blood sugar"]
    C --> C4["Sources: oats, fruit, pulses, barley"]

    style A fill:#4a90d9,color:#fff
    style B fill:#e67e22,color:#fff
    style C fill:#27ae60,color:#fff

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Sources of Dietary Fibre

Food Source	Type of Fibre	Key Details
Wholemeal bread	Mainly insoluble	Made from flour containing the whole grain, including the bran
Brown rice	Mainly insoluble	Retains the bran layer; higher in fibre than white rice
Wholegrain breakfast cereals	Both	Weetabix, Shredded Wheat, bran flakes, muesli, porridge oats
Oats and porridge	Mainly soluble	Contain beta-glucan, a soluble fibre shown to lower cholesterol
Fruit	Both	Apples, pears, oranges, bananas, berries — eat with skin where possible
Vegetables	Both	Carrots, broccoli, peas, sweetcorn, cabbage, Brussels sprouts
Pulses	Both	Lentils, chickpeas, kidney beans, baked beans — excellent sources
Nuts	Mainly insoluble	Almonds, walnuts, Brazil nuts
Seeds	Both	Chia seeds, flaxseeds, sunflower seeds, pumpkin seeds
Wholemeal pasta	Mainly insoluble	Higher in fibre than white pasta
Potato skins	Mainly insoluble	Eating potatoes with their skins increases fibre intake

Wholegrain vs Refined

Understanding the difference between wholegrain and refined is essential:

Term	Meaning	Example
Wholegrain	The entire grain is used, including the bran (outer layer), germ (seed), and endosperm (starchy centre)	Wholemeal flour, brown rice, porridge oats
Refined	The bran and germ have been removed during processing, leaving only the endosperm	White flour, white rice, white bread

Refining removes much of the fibre, B vitamins, and iron. This is why the government recommends choosing wholegrain carbohydrates where possible.

Exam Tip: A common exam question asks you to suggest how someone could increase their fibre intake. Always give specific swaps: replace white bread with wholemeal bread, white rice with brown rice, white pasta with wholemeal pasta, sugary cereal with porridge or bran flakes. Add fruit, vegetables, and pulses to meals.

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Functions of Dietary Fibre