Describe what is meant by a balanced diet and why it is important.

7.1 Human Nutrition – Diet

1. Objective

Describe what is meant by a balanced diet and why it is important.

2. Definition of a Balanced Diet (syllabus wording)

A balanced diet supplies the right amounts of the six essential nutrient groups so that the body can grow, repair tissue, obtain energy and carry out all its biochemical processes.

3. The Six (plus fibre) Essential Nutrient Groups

• Carbohydrates – the main source of short‑term energy for the brain and muscles.
• Proteins – supply amino acids required for growth, repair and maintenance of body tissues.
• Fats (lipids) – provide long‑term energy storage, insulation and enable absorption of the fat‑soluble vitamins A, D, E and K.
• Vitamins C & D – act as co‑enzymes or regulators in metabolic pathways.
  • Vitamin C prevents scurvy.
  • Vitamin D prevents rickets (with calcium).
• Mineral ions Ca & Fe – required in small amounts for specific physiological roles.
  • Calcium is essential for bone mineralisation.
  • Iron is required for haemoglobin synthesis; its deficiency causes iron‑deficiency anaemia.
• Water – the universal solvent. Its four key functions are:
  • Solvent for biochemical reactions.
  • Transport of nutrients, gases and waste products.
  • Regulation of body temperature (through sweating and evaporation).
  • Removal of metabolic waste (urine, faeces).
• Fibre (roughage) – an indigestible carbohydrate that:
  • Promotes regular bowel movements.
  • Supports a healthy gut microbiota.
  • Helps lower blood cholesterol and stabilise blood glucose.

4. Why a Balanced Diet Is Important

1. Supports growth and development – adequate protein, calcium, iron, vitamin C and vitamin D are vital for children and adolescents.
2. Provides energy – carbohydrates and fats supply the fuel needed for daily activities and basal metabolic functions.
3. Maintains normal body functions – vitamins act as co‑enzymes, mineral ions act as structural components or carriers, and water enables transport and temperature control.
4. Prevents nutrient‑deficiency diseases:
   • Scurvy – lack of vitamin C.
   • Rickets – lack of vitamin D (and/or calcium).
   • Iron‑deficiency anaemia – lack of iron.
5. Reduces risk of chronic diseases – sufficient fibre, unsaturated fats and antioxidant vitamins lower the chances of heart disease, type‑2 diabetes and some cancers.
6. Promotes good digestive health – fibre ensures regular bowel movements and a balanced gut microbiome.
7. Ensures proper hydration – water is required for nutrient transport, temperature regulation and waste elimination.

5. Key Food Groups, Main Nutrients (syllabus‑required examples in bold) and Typical Sources

6. Recommended Proportions – “½‑¼‑¼” Plate Model

Although not a compulsory part of the syllabus, the “½‑¼‑¼” visual guide is useful for exam answers.

• ½ of the plate – fruit and vegetables (vitamins, minerals, fibre, roughage).
• ¼ of the plate – starchy carbohydrates (energy‑providing carbohydrates).
• ¼ of the plate – protein‑rich foods (protein, iron, zinc, B‑vitamins).
• Add a small portion of dairy or a calcium‑rich alternative and a modest amount of healthy fats.

This model helps students translate “balanced diet” into a concrete, exam‑style answer.

7. Key Points to Remember

• “Balance” means obtaining the right proportion of each of the six essential nutrient groups (plus fibre), not merely eating a variety of foods.
• Portion size matters – excess of any nutrient (e.g., too much fat or sugar) can be harmful.
• Whole, minimally processed foods generally supply nutrients more efficiently than highly processed alternatives.
• Regular meals and healthy snacks maintain steady energy levels and help prevent overeating.
• Remember the four syllabus‑specific nutrients and the diseases they prevent:
  • Vitamin C – scurvy
  • Vitamin D – rickets
  • Calcium – rickets (with vitamin D)
  • Iron – iron‑deficiency anaemia