Describe the dietary importance of each of the main food groups and of water and dietary fibre.

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Human Nutrition – Diet (IGCSE 0610)

Objective

Describe the dietary importance of each main food group and of water and dietary fibre.

Balanced diet

A balanced diet supplies adequate amounts of carbohydrates, proteins, fats, vitamins, minerals, water and fibre to meet the body’s energy needs, support growth and repair, and maintain good health. It prevents nutritional deficiencies, excesses and the long‑term diseases associated with an unbalanced intake.

Main food groups

1. Carbohydrates

Key function Principal sources (principal source highlighted) Deficiency effects
Primary energy source; supplies glucose for brain, muscles and other cells; spares protein from being used for energy; provides dietary fibre when from whole grains.
  • Whole‑grain cereals (principal source of complex carbohydrates)
  • Rice, potatoes, pasta, bread
  • Fruit, legumes
 Low energy, fatigue, irritability; severe restriction can lead to ketosis.

2. Proteins

Key function Principal sources (principal source highlighted) Deficiency effects
Supply amino acids for growth, repair and maintenance of tissues; form enzymes, hormones, antibodies and structural cell components.
  • Meat, fish, eggs, dairy (principal source of high‑quality animal protein)
  • Beans, lentils, nuts, soy products (principal source of plant protein)
 Stunted growth, muscle wasting, weakened immunity, oedema (kwashiorkor).

3. Fats (Lipids)

Key function Principal sources (principal source highlighted) Deficiency effects
Concentrated energy (9 kcal g⁻¹); provide essential fatty acids (ω‑3, ω‑6); enable absorption of vitamins A, D, E, K; insulate and protect organs.
  • Vegetable oils, butter, margarine (principal source of dietary fat)
  • Nuts, seeds, avocado, fatty fish
 Dry skin, hair loss, poor wound healing, deficiency of fat‑soluble vitamins.

4. Vitamins (focus on C & D)

Vitamin Key role Principal sources (principal source highlighted) Deficiency cause & symptoms
Vitamin C Collagen synthesis, antioxidant, enhances iron absorption.
  • Citrus fruits, strawberries, kiwi, peppers, broccoli (principal source of vitamin C)
 Cause: inadequate intake of citrus fruit/vegetables → scurvy (bleeding gums, bruising, poor wound healing).
Vitamin D Promotes calcium absorption; essential for bone mineralisation.
  • Sunlight exposure (principal source of vitamin D)
  • Fortified milk, oily fish, egg yolk (dietary sources)
 Cause: insufficient sunlight and/or dietary intake → rickets in children, osteomalacia in adults.

5. Minerals (focus on calcium & iron)

Mineral Key function Principal sources (principal source highlighted) Deficiency effects
Calcium Bone & teeth formation, muscle contraction, blood clotting.
  • Milk, cheese, yogurt, fortified plant milks (principal source of calcium)
  • Leafy greens (supplementary source)
 Osteoporosis, rickets, muscle cramps.
Iron Component of haemoglobin; transports oxygen in the blood.
  • Red meat, poultry, fish (principal source of haem iron)
  • Beans, lentils, fortified cereals (principal source of non‑haem iron)
 Iron‑deficiency anaemia – fatigue, pallor, reduced exercise tolerance.

Water

  • Water is a principal component of a balanced diet. It acts as a solvent, transports nutrients and wastes, regulates temperature and provides a medium for biochemical reactions.
  • Average adult requirement: 1.5–2 L of fluid per day (more in hot climates or during vigorous exercise).
  • Key functions
    1. Maintains blood volume and pressure.
    2. Facilitates digestion, absorption and transport of nutrients.
    3. Allows excretion of metabolic wastes (urine, sweat, breath).
    4. Regulates body temperature through sweating and evaporation.
  • Signs of dehydration: thirst, dry mouth, dark urine, reduced urine output, dizziness, rapid pulse.
  • Severe loss (e.g., intense exercise, fever) must be replaced promptly to avoid heat‑related illness.

Dietary fibre

  • Indigestible plant carbohydrates that pass largely unchanged through the gut.
  • Types
    • Soluble fibre – forms a gel; helps lower blood cholesterol and moderates glucose absorption.
    • Insoluble fibre – adds bulk; promotes regular bowel movements.
  • Functions
    1. Prevents constipation and supports a healthy colon.
    2. Modulates post‑prandial blood glucose levels.
    3. Reduces blood cholesterol, lowering heart‑disease risk.
    4. Increases satiety, assisting weight management.
  • Major sources: whole grains, cereals with bran, fruits (especially with skin), vegetables, legumes, nuts and seeds.
  • Recommended intake: about 25 g per day for adolescents and adults.
  • Deficiency effects: constipation, increased risk of colorectal cancer, unfavourable blood lipid profile.
Suggested diagram: a balanced plate showing appropriate portions of carbohydrates, proteins, fats, vegetables, fruit and a glass of water.

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