A balanced diet is a diet that contains all the classes of food in the correct proportions to meet the body's needs for energy, growth and health.
Classes of food
- Carbohydrates — the main source of energy.
- Proteins — for growth and repair of tissues.
- Lipids (fats) — energy store and insulation.
- Vitamins — needed in tiny amounts to keep the body working (e.g. vitamin C, D).
- Minerals — e.g. calcium for bones, iron for haemoglobin.
- Water — a solvent and transport medium; makes up most of the body.
- Dietary fibre — not digested, but prevents constipation.
Key idea
A balanced diet must supply energy foods, body-building foods and protective foods, plus water and fibre, in the right amounts for that individual.
Factors affecting dietary needs
| Factor | Effect |
|---|---|
| Age | Growing children and teenagers need more protein per kg. |
| Sex | Males often need more energy due to greater muscle mass. |
| Activity/occupation | Active work needs more energy (kJ). |
| Pregnancy | Extra protein, iron and calcium are needed. |
| Health | Illness or recovery may change needs. |
Energy balance
If energy intake equals energy used, body mass stays stable. Taking in more energy than is used leads to storage as fat and possible obesity; taking in too little leads to weight loss and, in severe cases, malnutrition.
Missing a food class causes deficiency diseases. Too little vitamin C causes scurvy; too little iron causes anaemia; too little calcium weakens bones. This is why variety matters: no single food supplies every nutrient, so a balanced diet combines many foods to cover all the body's needs.
Example
A construction worker doing heavy physical work needs more carbohydrate each day than an office worker of the same age and size, because more energy is used.
Remember
Balanced does not mean equal amounts of everything — it means the right proportions for the person's age, sex and activity.