Food and nutrients
Food supplies energy, materials for growth and repair, and substances that regulate body processes. The main nutrient groups are carbohydrates, proteins, lipids, vitamins, mineral salts, water, and dietary fibre.
| Nutrient | Main role | Examples of sources |
|---|---|---|
| Carbohydrates | Energy supply | Cereals, potatoes, fruits, and sugars |
| Proteins | Growth and repair | Meat, fish, eggs, beans, and nuts |
| Lipids | Energy store, insulation, and cell membranes | Oils, butter, seeds, and nuts |
| Vitamins and mineral salts | Regulation and healthy body function | Fruits, vegetables, milk, and varied foods |
| Fibre and water | Healthy digestion and transport | Plant foods and fluids |
Food tests
- Starch: iodine solution changes from brown to blue-black.
- Reducing sugar: Benedict’s solution gives a coloured precipitate after heating when reducing sugar is present.
- Protein: the biuret test produces a violet colour.
- Fat: the ethanol emulsion test produces a cloudy white emulsion.
Balanced diet
A balanced diet provides all required nutrients in suitable proportions. Requirements vary with age, sex, activity, pregnancy, illness, and the environment. An unbalanced diet may cause deficiency diseases, obesity, or poor growth.
Revision questions
- State the main function of carbohydrates, proteins, and lipids.
- Describe the test for starch.
- What is a balanced diet?
- Explain why nutrient requirements vary between people.
