Diet

1. Overview

Diet refers to the food and drink consumed by an organism. This topic explores the components of a balanced diet, the specific biological roles of different nutrients, and the health consequences that arise when certain essential substances are missing from our intake.

Key Definitions

• Balanced Diet: A diet that contains all the essential nutrients (carbohydrates, fats, proteins, vitamins, minerals, fibre, and water) in the correct proportions to maintain health.
• Nutrient: A substance that provides nourishment essential for the maintenance of life and for growth.
• Deficiency Disease: A disease caused by the lack of an essential nutrient in the diet.
• Peristalsis: The wave-like muscular contractions of the digestive tract that move food along, aided specifically by dietary fibre.

Core Content

The Balanced Diet

A balanced diet is not the same for everyone; it varies depending on:

• Age: Children need more protein for growth and more energy per gram of body mass.
• Gender: Generally, males have higher energy requirements; females may require more iron due to menstruation.
• Activity Level: Active individuals require more carbohydrates for cellular respiration.
• Pregnancy/Lactation: Pregnant women need more energy, calcium, and iron to support fetal development.

Principal Dietary Sources and Importance

Nutrient	Principal Sources	Biological Importance / Function
(a) Carbohydrates	Rice, pasta, bread, potatoes	Primary source of energy for cellular respiration.
(b) Fats and Oils	Butter, oil, nuts, fatty fish	Long-term energy storage, thermal insulation, and making cell membranes.
(c) Proteins	Meat, fish, eggs, beans	Growth and repair of tissues; making enzymes and antibodies.
(d) Vitamin C	Citrus fruits (lemons, oranges)	Used in the synthesis of collagen (protein for skin, hair, and gums).
(e) Vitamin D	Eggs, oily fish, made in skin by sunlight	Helps the body absorb calcium for strong bones and teeth.
(f) Calcium (ion)	Milk, cheese, green leafy vegetables	Required for strong bones and teeth; essential for blood clotting.
(g) Iron (ion)	Red meat, spinach, liver	Component of haemoglobin; used to transport oxygen in red blood cells.
(h) Fibre	Vegetables, wholemeal bread, fruit	Provides bulk to help food move through the gut via peristalsis; prevents constipation.
(i) Water	Drinks, juicy fruits/vegetables	Acts as a solvent for chemical reactions; used for transport (blood) and temperature regulation (sweat).

Deficiency Diseases

• Scurvy:
  • Cause: A deficiency of Vitamin C.
  • Symptoms: Bleeding gums, loss of teeth, and wounds that do not heal properly because the body cannot produce enough collagen.
• Rickets:
  • Cause: A deficiency of Vitamin D or Calcium.
  • Symptoms: Softening and weakening of the bones, which can lead to "bow-leggedness" or bone deformities in children.

Extended Content (Extended Only)

There are no specific supplemental learning objectives for Topic 7.1: Diet.

Key Equations

There are no specific mathematical equations for this sub-topic; however, students should be able to compare nutritional data in tables.

Worked Example: Calculating Percentage Energy If a food item contains 2000kJ of total energy and 500kJ comes from fat:

• $\text{Percentage energy from fat} = (\frac{\text{Energy from fat}}{\text{Total energy}}) \times 100$
• $(500 \div 2000) \times 100 = 25%$

Common Mistakes to Avoid

• ❌ Wrong: Fibre is a nutrient that provides us with energy.
• ✓ Right: Fibre cannot be digested; its role is to provide bulk to the diet to help food move through the alimentary canal.
• ❌ Wrong: Vitamin D and Calcium have the same function.
• ✓ Right: While both are related to bone health, Calcium is the structural material, and Vitamin D is the chemical that allows the body to absorb and use that calcium.
• ❌ Wrong: Everyone needs the same "Balanced Diet."
• ✓ Right: A balanced diet is specific to an individual's age, gender, and activity level.

Exam Tips

• Command Words: If a question asks you to "State," provide a short, one-word or one-sentence answer (e.g., "Iron"). If it asks you to "Describe," you must explain the source or the function in more detail.
• Real-World Contexts: Expect questions comparing the diets of different people (e.g., an office worker vs. a marathon runner). Always link your answer to energy requirements or tissue repair.
• Typical Values: While you don't need to memorize exact numbers, remember that fat contains roughly twice as much energy per gram (37kJ/g) as carbohydrates or proteins (17kJ/g).
• Hemoglobin Link: When discussing Iron, always mention "haemoglobin" and "oxygen transport" to get the full biological marks.