A balanced diet and energy needsSpec 2.24, 2.26
In short
A balanced diet contains the right proportions of carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre. Most energy comes from carbohydrate and lipid. Energy requirements vary with activity level, age and pregnancy: more active people respire more in their muscles, teenagers are growing quickly, and pregnant women need extra energy for the growth of the fetus.
A balanced diet contains the right proportions of all seven components: carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre. Most of the energy in a diet comes from carbohydrate and lipid. Smaller amounts are needed of vitamins and minerals, but they are still essential.
- Carbohydrate and lipid: the main sources of energy, so they are needed in larger amounts.
- Protein: needed for growth and repair of tissues.
- Vitamins and minerals: needed in small amounts to stay healthy.
- Water: needed in large amounts, because the body loses it all the time.
- Dietary fibre: needed to keep food moving through the gut.
The amount of energy a person needs each day depends on how much energy their body uses. Energy requirements vary with activity level, age and pregnancy.
| Factor | Effect on energy needed | Why |
|---|---|---|
| Activity level | More active people need more energy | Contracting muscles use energy from respiration. A person who trains or has a physical job respires more than a person who sits at a desk. |
| Age | Teenagers need more energy than young children. Older adults need less than younger adults. | Teenagers are larger and growing quickly. Older people are usually less active and are no longer growing. |
| Pregnancy | A pregnant woman needs more energy | Extra energy is needed for the growth of the fetus and for the changes in the mother's body. |
If a person takes in more energy than they use, the extra is stored, mainly as fat. If a person takes in less energy than they use, they lose body mass.
A balanced diet is about the right proportions, not the same amount of each nutrient. For energy questions, link the answer to respiration: more activity means more muscle contraction, so more respiration and more energy needed.
Written and checked against the Edexcel IGCSE Biology (4BI1) specification · Updated October 2026