Balanced Diet and the Six Classes of Nutrients
A balanced diet is one that supplies, in the right proportions, all the nutrients the body needs for growth, repair, energy and regulation. No single food contains every nutrient — variety is the foundation of nutrition.
A diet that provides adequate amounts of carbohydrates, proteins, fats, vitamins, minerals and water — in proportions appropriate to age, sex, activity level and physiological state (e.g. pregnancy) — to maintain health and prevent disease.
The six classes of nutrients
- Carbohydrates (4 kcal/g) — main energy source. Whole grains, fruit, vegetables, pulses. Should provide ~50–60% of daily energy.
- Proteins (4 kcal/g) — body-building and repair. Meat, fish, eggs, milk, pulses, soya. ~10–15% of energy.
- Fats (9 kcal/g) — concentrated energy, source of essential fatty acids, vehicle for fat-soluble vitamins. ~25–30% of energy; prefer unsaturated.
- Vitamins — organic micronutrients required in tiny amounts but essential for metabolism. Water-soluble (B-complex, C) and fat-soluble (A, D, E, K).
- Minerals — inorganic micronutrients: calcium, iron, iodine, zinc, sodium, potassium, magnesium, phosphorus.
- Water — the universal solvent. Roughly 2–3 litres a day from food and drink combined.
- The body is roughly 60% water by weight.
- Essential nutrients are those the body cannot synthesise and must obtain from food (essential amino acids, essential fatty acids, vitamins, most minerals).
- A calorie in nutrition is technically a kilocalorie (kcal) — the energy needed to raise 1 kg of water by 1 °C.
- Average adult energy requirement: ~2000 kcal/day for women, ~2500 kcal/day for men.
Common deficiency diseases
| Nutrient | Deficiency disease | Key signs |
|---|---|---|
| Vitamin A | Night blindness, xerophthalmia | Poor night vision, dry cornea |
| Vitamin B1 (thiamine) | Beriberi | Weakness, nerve damage |
| Vitamin B3 (niacin) | Pellagra | Dermatitis, diarrhoea, dementia |
| Vitamin C (ascorbic acid) | Scurvy | Bleeding gums, weakness |
| Vitamin D | Rickets (children), osteomalacia (adults) | Soft, deformed bones |
| Iron | Iron-deficiency anaemia | Fatigue, pallor |
| Iodine | Goitre, cretinism | Swollen thyroid, impaired development |
| Calcium | Osteoporosis | Brittle bones |
| Protein | Kwashiorkor, marasmus | Stunting, oedema, muscle wasting |
Iodised salt is one of the most cost-effective public-health interventions ever devised. Adding a few parts per million of potassium iodide to ordinary table salt prevents goitre and protects fetal brain development.
Reading a food label
Look for these on any packet:
- Serving size — all other numbers are per serving.
- Energy (kcal or kJ) per serving.
- Macronutrients — carbohydrate (of which sugars), fat (of which saturates), protein.
- Sodium — high levels (>1.5 g per 100 g) are a red flag.
- Fibre — aim for >3 g per serving.
- Ingredients list — in descending order by weight.
- Date marking — use-by (food safety) vs best-before (quality only).
The food pyramid or its modern replacement the food plate is a visual reminder: half the plate vegetables and fruits, a quarter whole grains, a quarter protein, with limited fats and sugars.