Diet

A balanced diet contains the right amounts of carbohydrates (energy), fats (energy store, insulation), proteins (growth and repair), vitamins (C for healthy skin and gums; D for absorbing calcium), minerals (calcium for bones and teeth; iron for haemoglobin), fibre (helps food move through the gut) and water. Lack of a nutrient causes deficiency diseases: scurvy (vitamin C), rickets (vitamin D or calcium), anaemia (iron). Energy needs depend on age, sex, activity and pregnancy.

Cambridge 5090 Paper 1Cambridge 5090 Paper 2Cambridge 0610 Papers 2, 4Cambridge 0610 Papers 1, 3Edexcel 4BI1 Paper 1BEdexcel 4BI1 Paper 2B≈ 35 minRevision 1 · updated 2026-10-30

Section 1 of 14

Learning objectives

Name the nutrients in a balanced diet, with sources and functions.
Link deficiency diseases to missing nutrients.
Explain how energy needs vary and calculate energy in food.

Pause and think

Sailors on long voyages in the 1700s often got scurvy, with bleeding gums. A diet of salted meat and biscuits was to blame. What was missing?

Section 2 of 14

Core idea

Start hereYou are what you eat

Every protein in your muscles, every iron atom in your blood and every calcium ion in your bones came from food. Leave something out, and the body shows it.

The big idea

A balanced diet supplies energy, materials for growth, and small amounts of vitamins and minerals. Each missing nutrient causes a specific deficiency disease.

1. Nutrients

Seven components of a balanced diet

Drawing diagram…

Energy, building, protection and transport.

2. Measuring energy in food

Worked exampleBurning a crisp

A 0.80 g crisp heats 20 g of water from 21 °C to 57 °C.

Goal: Energy per gram.
Strategy: $E=m\times4.2\times\Delta T$ , then divide by mass of food.

$\Delta T=36\,^\circ\mathrm{C}$
Temperature rise.
$E=20\times4.2\times36=3024\ \text{J}$
Energy absorbed by water.
$\frac{3024}{0.80}=3780\ \text{J/g}$
Per gram of food.

AnswerAbout

3.8

kJ/g.

✓ CheckLower than the label value because heat is lost ✓.

Key takeawayDeficiencies Vitamin C → scurvy; vitamin D / calcium → rickets; iron → anaemia; protein → kwashiorkor.

Pause and think

Why might an athlete eat more carbohydrate before a race?

Summary

Seven components.
Deficiency diseases.
Energy needs vary.

Balanced diet: All nutrients in the right proportions.
Deficiency disease: Illness caused by lack of a nutrient.
Fibre: Indigestible plant material that aids peristalsis.

HistoryJames Lind. In 1747 naval surgeon James Lind gave sailors with scurvy different treatments. Those given oranges and lemons recovered within days: one of the first controlled clinical trials.

Fun factSunshine vitamin. Your skin makes vitamin D when exposed to sunlight, which is why rickets returned in some northern cities where children spent less time outdoors.

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