Carbohydrate is one of the three macronutrients you need to understand for AQA GCSE Food Preparation and Nutrition. It includes sugars, starch and non-starch polysaccharides, often called dietary fibre. These types of carbohydrate have different structures, sources and functions in the body. Knowing the differences helps you explain why foods behave differently during cooking and how a balanced diet can include carbohydrate-rich foods. This guide covers the key theory for AQA specification section 3.2.1.3, with practical examples and exam-ready points for Years 10 and 11.
What is carbohydrate?
Carbohydrate is a macronutrient, meaning a nutrient needed by the body in relatively large amounts. Its main function is to provide energy. During digestion, many carbohydrates are broken down into glucose. Glucose can then be used by cells during respiration to release energy for movement, growth, repair and normal body processes.
Carbohydrates are found mainly in plant foods, although lactose, the sugar in milk, is an animal-derived carbohydrate. The three key groups to learn are sugars, starch and non-starch polysaccharides.
Sugars
Sugars are simple carbohydrates. They have relatively small molecules and are usually sweet in taste. Sugars can be divided into monosaccharides and disaccharides.
Monosaccharides
Monosaccharides are single sugar units. Examples include:
- Glucose, found in fruits, vegetables and some sweet foods.
- Fructose, found naturally in fruit and honey.
- Galactose, which is part of the sugar lactose.
Disaccharides
Disaccharides contain two linked sugar units. Examples include:
- Sucrose, made from glucose and fructose, and found in table sugar, fruit and some vegetables.
- Lactose, found in milk and dairy products.
- Maltose, formed when starch is broken down, including during the malting of grains.
Sugars can dissolve easily in liquid. In cooking, sugar can add sweetness, help foods brown and affect texture. For example, sugar contributes to the colour and flavour of baked goods. Heating sugar can cause caramelisation, a chemical change that produces a brown colour and characteristic flavour.
Starch
Starch is a complex carbohydrate, also called a polysaccharide. It is made from many glucose units joined together. Plants store carbohydrate as starch, so good sources include potatoes, bread, rice, pasta, cereals, flour, beans and other starchy foods.
Starch is not usually sweet. It must be digested into smaller molecules before the body can use the glucose. It is an important source of energy in the diet and is particularly useful in meals such as pasta with vegetables, rice dishes or potato-based meals.
Starch in practical food preparation
Starch affects the texture of food during cooking. When starch is heated with liquid, the starch granules absorb water, swell and thicken the mixture. This process is called gelatinisation. It is important when making a white sauce, custard or gravy. If flour is blended with fat first to make a roux, the liquid can then be added gradually while stirring to produce a smoother sauce.
Starch can also contribute to browning and flavour when dry foods are heated. For example, the surface of bread or pastry changes during baking. The exact changes depend on the ingredients, temperature and amount of moisture present.
Non-starch polysaccharides and dietary fibre
Non-starch polysaccharides, usually shortened to NSP, are a group of complex carbohydrates found in the cell walls of plants. In everyday nutrition language, they are commonly discussed as dietary fibre. Fibre is not fully digested in the small intestine, so it does not provide energy in the same way as digestible carbohydrate.
Good sources include wholemeal bread, wholegrain breakfast cereals, brown rice, wholewheat pasta, fruit, vegetables, peas, beans, lentils, nuts and seeds. Fibre helps add bulk to the contents of the digestive system and supports normal bowel function. A varied diet containing fibre-rich foods also helps meals feel more filling.
When revising, do not describe fibre simply as another type of sugar or starch. Fibre is carbohydrate, but its structure means it is not digested in the same way as digestible carbohydrate.
Comparing the three types
| Type | Structure | Examples and sources | Key points |
|---|---|---|---|
| Sugars | Simple carbohydrates: monosaccharides or disaccharides | Fruit, honey, table sugar, milk | Often sweet and soluble; provide energy after digestion |
| Starch | Polysaccharide made from many glucose units | Potatoes, bread, rice, pasta, cereals and flour | Important energy source; thickens mixtures during gelatinisation |
| NSP or dietary fibre | Complex plant carbohydrates that are not fully digested | Wholegrains, fruit, vegetables, beans, nuts and seeds | Adds bulk and supports normal bowel function |
Carbohydrate and a balanced diet
A balanced diet includes a suitable variety of carbohydrate-containing foods. Starchy foods can provide energy, while fruit, vegetables and wholegrain foods can provide fibre as well as vitamins and minerals. Foods containing sugars can be included, but the overall balance of the diet matters. Frequent consumption of sugary foods and drinks can increase the risk of dental caries, especially when oral hygiene is poor.
When answering an exam question, avoid saying that all carbohydrate is unhealthy or that all carbohydrate has the same effect. Instead, identify the type, give a relevant source and explain its function. Remember that individual dietary needs vary. Healthy-eating guidance can change, so use the current advice from the NHS or Food Standards Agency when required.
Exam-ready retrieval checklist
- Can you define a macronutrient and state the main function of carbohydrate?
- Can you distinguish between a monosaccharide, disaccharide and polysaccharide?
- Can you give examples of glucose, fructose, sucrose, lactose and starch?
- Can you name sources of starch and dietary fibre?
- Can you explain why fibre is not digested in the same way as starch?
- Can you define gelatinisation and link it to a sauce, custard or gravy?
- Can you explain how sugar contributes to sweetness and caramelisation?
- Can you apply the theory to a realistic food product or cooking method?
For the wording and detail required by your course, compare your notes with the AQA Food Preparation and Nutrition specification. Always check the current official specification and current NHS or Food Standards Agency guidance, as information can be updated.