What are the different types of carbohydrate, what do they do, and why does fibre matter?
Carbohydrates as a macronutrient: monosaccharides, disaccharides and polysaccharides, free sugars and starch, dietary fibre (NSP), the functions and food sources of carbohydrate, and the dietary recommendations for sugar and fibre.
A CCEA A-Level Nutrition and Food Science answer on carbohydrates: monosaccharides, disaccharides and polysaccharides, free sugars and starch, dietary fibre (NSP), the functions and food sources of carbohydrate, and the recommendations for sugar and fibre intake.
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What this dot point is asking
CCEA wants you to classify carbohydrates as monosaccharides, disaccharides and polysaccharides, distinguish free sugars from intrinsic and milk sugars, describe starch and dietary fibre (NSP), explain the functions and sources of carbohydrate, and state the dietary recommendations for sugar and fibre.
Types of carbohydrate
Starch is the storage carbohydrate of plants and the main dietary source of energy, found in bread, pasta, rice, potatoes and cereals. It is digested to glucose, which the body uses for energy or stores as glycogen in the liver and muscles. Free sugars are sugars added to food plus those naturally present in honey, syrups and unsweetened fruit juice; the sugars locked inside whole fruit and vegetables (intrinsic sugars) and the lactose in milk are not free sugars.
Functions, sources and recommendations
Dietary advice is that starchy carbohydrates should make up about a third of the diet (the largest segment of the Eatwell Guide), ideally wholegrain, while free sugars should provide no more than about 5 percent of total food energy (roughly 30 g a day for an adult). High free-sugar intake is linked to dental caries, excess energy and weight gain, and type 2 diabetes risk, which connects this nutrient to the diet-and-health content of the course.
Examples in context
Example 1. Swapping refined for wholegrain. A diet of white bread, white rice and sugary cereals is low in fibre and high in rapidly digested starch and free sugar. Swapping to wholemeal bread, brown rice and porridge oats raises fibre towards the 30 g target, slows glucose absorption, increases satiety and improves bowel health. This single change touches weight management, blood glucose control and bowel-cancer risk, all examined later in the course.
Example 2. Reading a drinks label. A pupil comparing a fizzy drink, a fruit juice and a glass of milk learns that the fizzy drink and the juice both count as free sugars (added sugar and the released sugar of juice), while the lactose in milk does not. The milk also supplies calcium and protein. This shows how the free-sugar definition guides real food choice rather than simply counting total sugar.
Try this
Q1. Name the two monosaccharides that make up sucrose. [2 marks]
- Cue. Glucose and fructose.
Q2. State two roles of dietary fibre (NSP) in the body. [2 marks]
- Cue. Adds bulk and prevents constipation; promotes satiety; helps lower blood cholesterol; lowers bowel-cancer risk (any two).
Q3. State the recommended maximum intake of free sugars as a percentage of food energy. [1 mark]
- Cue. No more than about 5 percent of total food energy.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA AS 20186 marksDiscuss the importance of dietary fibre (NSP) in the diet and explain the consequences of a low fibre intake.Show worked answer →
A 6-mark answer needs the roles of fibre and the disorders linked to a low intake.
Dietary fibre, also called non-starch polysaccharide (NSP), is the indigestible part of plant foods. Insoluble fibre (in wholegrain cereals, wholemeal bread and the skins of fruit and vegetables) adds bulk to the faeces, holds water and speeds the passage of food through the gut. Soluble fibre (in oats, pulses, fruit and vegetables) forms a gel that slows the absorption of glucose and helps lower blood cholesterol.
Fibre therefore prevents constipation, promotes a feeling of fullness (satiety) that helps weight control, helps regulate blood glucose, and is associated with a lower risk of bowel (colorectal) cancer and coronary heart disease.
A low fibre intake is linked to constipation, haemorrhoids and diverticular disease, a greater risk of bowel cancer, poorer blood glucose control, and a tendency to overeat because low-fibre foods are less filling. The recommendation for adults is about 30 grams of fibre a day.
Markers reward the soluble and insoluble distinction with sources, at least two positive roles, the disorders linked to low intake, and the 30 g recommendation.
CCEA AS 20204 marksExplain the difference between free sugars and the sugars found naturally within whole fruit and milk.Show worked answer →
A 4-mark answer needs a definition of free sugars and a clear contrast with intrinsic and milk sugars.
Free sugars are those added to foods by the manufacturer, cook or consumer (such as table sugar and the sugar in cakes and fizzy drinks), plus the sugars naturally present in honey, syrups and unsweetened fruit juices. These are the sugars dietary advice tells us to reduce, because they raise the risk of dental caries and contribute extra energy with little other nutrition.
The sugars contained within the cellular structure of whole fruit and vegetables, and the lactose in milk and milk products, are not classed as free sugars. They are released more slowly, come packaged with fibre, vitamins and minerals, and are not the target of the reduction advice.
Markers reward a correct definition of free sugars including juice, honey and syrups, the contrast with intrinsic and milk sugars, and the reason free sugars are limited (dental caries, energy density).
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Sources & how we know this
- CCEA GCE Nutrition and Food Science specification — CCEA (2016)
- Carbohydrates and health (SACN report) — Scientific Advisory Committee on Nutrition (2015)