What are carbohydrates, why does the body need them, and what is the difference between sugars, starch and fibre?
Carbohydrate as a macronutrient: its function in the body, sugars (simple) and starch (complex), free sugars, dietary fibre, food sources, and the effects of too much or too little.
A focused answer to the WJEC Food Preparation and Nutrition principles of nutrition topic on carbohydrate, covering its function, simple sugars and complex starch, free sugars, dietary fibre, food sources, and the effects of eating too much or too little.
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What this dot point is asking
You need to know what carbohydrate does in the body, the difference between simple sugars and complex starch, what free sugars and dietary fibre are, the main food sources, and the effects of eating too much or too little.
The function of carbohydrate
Carbohydrate is a macronutrient and the body's main source of energy, providing about 4 kcal per gram. It is digested to glucose, which the body uses for energy; spare glucose can be stored or, if too much is eaten, turned into fat.
Simple and complex carbohydrates
- Simple carbohydrates (sugars): small molecules that are quickly digested, giving a fast but short-lived rise in energy. Sources: sugar, sweets, honey, jam, fruit and milk.
- Complex carbohydrates (starch): many sugar units joined together, digested more slowly, giving a steadier, longer-lasting release of energy. Sources: bread, rice, pasta, potatoes and cereals.
Starchy foods are the largest section of the Eatwell Guide, so meals should be based on them, choosing wholegrain where possible.
Free sugars
The advice is to cut down on free sugars, because they cause tooth decay, provide "empty calories" and contribute to weight gain and type 2 diabetes.
Dietary fibre
Dietary fibre (NSP) is carbohydrate the body cannot digest. It:
- adds bulk and helps food move through the gut, preventing constipation,
- keeps the bowel healthy and lowers the risk of bowel disease,
- helps you feel full, which helps control weight.
Sources: wholegrain bread and cereals, brown rice and pasta, fruit and vegetables (with skins), beans and pulses. Adults are advised to aim for about 30 g of fibre a day, and the simplest way to get there is to choose wholegrain versions of starchy foods and to eat plenty of fruit, vegetables and pulses.
Reading the label for sugar
Nutrition labels show carbohydrate and, beneath it, "of which sugars", which helps you compare products and spot foods high in free sugars. Traffic-light colours flag foods that are high (red), medium (amber) or low (green) in sugar. Swapping a sugary drink for water, or sugary cereal for plain wholegrain cereal, are easy ways to cut free sugars while keeping the energy and fibre from starchy carbohydrate.
The effects of too much or too little carbohydrate
Too much:
- spare carbohydrate is stored as fat, leading to weight gain,
- too many free sugars cause tooth decay and raise the risk of type 2 diabetes.
Too little:
- the body is short of its main energy source, causing tiredness,
- too little fibre leads to constipation and poor bowel health.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style4 marksExplain the difference between simple and complex carbohydrates and give a food example of each.Show worked answer →
A 4-mark question. Award marks for the distinction and correct examples.
Simple carbohydrates are sugars, which are quickly digested and give a fast, short-lived rise in energy, for example sweets, sugar, fruit and honey. Complex carbohydrates are starches, which are made of many sugar units joined together, are digested more slowly and give a steadier, longer-lasting release of energy, for example bread, rice, pasta and potatoes. Choosing complex carbohydrates, especially wholegrains, also provides fibre.
Markers reward: simple carbohydrates are sugars giving quick energy with examples; complex carbohydrates are starches giving slower, longer energy with examples; and ideally the fibre point for wholegrains.
WJEC style3 marksDescribe how dietary fibre helps to keep the body healthy.Show worked answer →
A 3-mark question on fibre.
Dietary fibre (NSP) adds bulk to food and helps it move through the digestive system, which prevents constipation. It helps keep the bowel healthy and lowers the risk of bowel diseases such as bowel cancer. It also helps you feel full, so you are less likely to overeat, which helps control weight.
Markers reward: aids movement of food through the gut and prevents constipation; keeps the bowel healthy and lowers disease risk; and helps you feel full to control weight.
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Sources & how we know this
- WJEC Eduqas GCSE Food Preparation and Nutrition specification (from 2016) — WJEC Eduqas (2016)