Biology (0610) | Diet

👋 Welcome to the Diet Chapter Study Notes!

Hi future Biologists! This chapter is all about what we eat and why it matters for our bodies to grow, move, and stay healthy. Understanding diet is fundamental to human biology, and the concepts here are easy to relate to your everyday life.

Don't worry if this seems tricky at first—we will break down the components of food into simple, easy-to-remember roles!

7.1 The Balanced Diet

What is a Balanced Diet?

A balanced diet is simply a diet that contains all the essential components of food—carbohydrates, fats, proteins, vitamins, minerals, fibre, and water—in the correct proportions and quantities to maintain good health.

Think of your body like a car. You need petrol (energy from carbs/fats), but you also need oil (vitamins/minerals for the engine to run smoothly) and water (transport and cooling). A balanced diet provides all these things!

Key Takeaway:

A balanced diet must supply energy for activities and raw materials for growth, repair, and metabolism.

The Principal Dietary Components and Their Importance

1. Energy Providers (The Macronutrients)

These are needed in large amounts (macro) and their main job is to provide energy.

(a) Carbohydrates

• Importance: They are the main source of energy for the body, especially for intense activities and the brain.
• Sources: Starch (e.g., bread, potatoes, rice) and Sugars (e.g., fruit, honey).

(b) Fats and Oils (Lipids)

• Importance:
  • Provide a concentrated store of energy (more energy per gram than carbohydrates).
  • Act as insulation (keep you warm) and protection for organs.
  • They are essential for making cell membranes and hormones.
  • They help absorb certain vitamins (A, D, E, K).
• Sources: Butter, oil, nuts, seeds, fatty meat.

(c) Proteins

• Importance: Proteins are essential for growth and repair of cells and tissues. They are used to make vital substances like:
  • Enzymes (biological catalysts).
  • Hormones (chemical messengers, like insulin).
  • Antibodies (for the immune system).
• Sources: Meat, fish, eggs, beans, pulses. (Proteins are built from smaller units called amino acids.)

2. Regulators (Vitamins and Mineral Ions)

These are the micronutrients—needed in small (micro) quantities but are absolutely vital for chemical reactions and health.

(d) Vitamins (Limited to C and D)

• Vitamin C
  • Importance: Essential for maintaining healthy connective tissue, skin, blood vessels, and healing wounds. It's also important for the immune system.
  • Sources: Citrus fruits (oranges, lemons), leafy vegetables.
• Vitamin D
  • Importance: Helps the body absorb calcium and phosphate, which are necessary for strong bones and teeth.
  • Sources: Oily fish, eggs, fortified dairy products. Our skin also makes Vitamin D when exposed to sunlight.

(e) Mineral Ions (Limited to Calcium and Iron)

• Calcium (ion)
  • Importance: Building strong bones and teeth. It is also required for blood clotting and muscle contraction.
  • Sources: Milk, cheese, leafy green vegetables (like kale).
• Iron (ion)
  • Importance: Needed to make haemoglobin, the protein in red blood cells that carries oxygen around the body.
  • Sources: Red meat, liver, spinach, fortified cereals.

3. Other Essentials (Fibre and Water)

(f) Fibre (Roughage)

• Importance: Fibre consists of plant material (mostly cellulose) that humans cannot digest.
  • It adds bulk to food, stimulating the muscle contractions (peristalsis) of the alimentary canal.
  • This keeps food moving and prevents constipation (difficulty passing faeces).
• Sources: Whole grains, cereals, fruits, vegetables.

(g) Water

• Importance: Water is the most important component of the body (making up about 70% of our mass!).
  • It acts as a solvent, allowing substances like nutrients, ions, and waste products (urea) to be transported in the blood and other fluids.
  • It helps control body temperature (via sweating).
  • It is essential for metabolic reactions and excretion.
• Sources: Drinking water, juices, and most foods (like fruits and vegetables).

Deficiency Diseases (7.1.3)

If you miss out on certain vital nutrients for a long time, you can develop deficiency diseases. The syllabus requires you to know the causes of two specific diseases:

1. Scurvy

• Cause: Lack of Vitamin C.
• Symptoms: Weakness, bleeding gums, and delayed healing of wounds.
• Historical Note: Scurvy was common among sailors on long voyages who had no access to fresh fruit and vegetables.

2. Rickets

• Cause: Lack of Vitamin D or calcium.
• Symptoms: Softening and weakening of bones, leading to skeletal deformities (e.g., bowed legs in children).