Balanced Diet

Definition and Components

A balanced diet contains appropriate amounts of nutrients needed for health, growth and energy. It provides all essential nutrients in correct proportions.

Nutrient Categories and Functions

Nutrient Main Functions Key Sources
Carbohydrates Energy source Bread, rice, pasta, potatoes, cereals
Fats/Oils Energy storage, insulation, cell membrane Butter, oil, meat, nuts, seeds
Proteins Growth, repair, enzymes, hormones Meat, fish, eggs, milk, beans, nuts
Vitamins Metabolic functions, defence, vision Fruits, vegetables, dairy
Minerals Structure, enzymes, nerve function Dairy, meat, leafy greens, nuts
Fibre Digestive health, waste removal Whole grains, fruits, vegetables, legumes
Water Transport, temperature control, reactions Water, drinks, food

Detailed Nutrient Information

Carbohydrates

  • Sources: Bread, rice, pasta, potatoes, cereals, fruits, vegetables
  • Function: Main energy source for cells
  • Storage: Excess stored as glycogen in liver and muscles
  • Deficiency: Leads to fatigue, poor concentration, weight loss

Fats and Oils

  • Sources: Butter, cooking oil, meat, fish, nuts, seeds
  • Function: Long-term energy storage, thermal insulation, cell membranes
  • Types:
    • Saturated: Solid at room temperature (animal fats)
    • Unsaturated: Liquid at room temperature (plant oils)
  • Deficiency: Weight loss, poor cell membrane function

Proteins

  • Sources: Meat, fish, eggs, milk, soy, beans, nuts
  • Function: Growth, tissue repair, enzymes, antibodies, hormones
  • Building Blocks: Amino acids
  • Deficiency: Kwashiorkor (swollen belly, stunted growth, hair changes)

Vitamins

Vitamin Main Function Deficiency Disease Good Sources
Vitamin C Collagen synthesis, immune function, antioxidant Scurvy (bleeding gums, poor wound healing) Citrus fruits, berries, peppers
Vitamin D Calcium absorption, bone health Rickets (soft bones in children), osteomalacia Sunlight, fatty fish, fortified foods
Other B vitamins Energy release, nerve function Various neurological issues Whole grains, meat, eggs

Minerals

Mineral Main Function Deficiency Disease Good Sources
Calcium Bone and teeth structure, muscle function Rickets, osteoporosis Milk, cheese, leafy greens
Iron Oxygen transport in haemoglobin Anaemia (fatigue, pale skin) Red meat, spinach, lentils
Others Various metabolic functions Various Dairy, meat, nuts, grains

Fibre

  • Types:
    • Soluble: Dissolves in water (oats, beans)
    • Insoluble: Does not dissolve (wheat bran, vegetables)
  • Functions:
    • Promotes healthy bowel movements
    • Prevents constipation
    • Helps regulate blood sugar
    • Lowers cholesterol
  • Deficiency: Constipation, digestive problems

Water

  • Function: Transport of nutrients, temperature regulation, chemical reactions, waste removal
  • Recommended: 6-8 glasses daily
  • Sources: Water, drinks, food (fruits, vegetables, soups)

Digestive System

Overview

The digestive system breaks down food into small molecules that can be absorbed into the bloodstream for use by cells.

Alimentary Canal (Digestive Tract)

Main organs arranged sequentially:

  1. Mouth
  2. Oesophagus
  3. Stomach
  4. Small Intestine
  5. Large Intestine
  6. Rectum
  7. Anus

Associated Organs

These organs assist digestion but are not part of the alimentary canal:

Organ Function
Salivary glands Produce saliva containing amylase
Liver Produces bile for fat digestion
Gall bladder Stores and concentrates bile
Pancreas Produces digestive enzymes and hormones

Diagram showing alimentary canal and associated digestive organs

Digestive Processes

1. Ingestion

  • Taking food into the mouth
  • First step of digestion

2. Digestion

Breaking down food into smaller molecules. Two types:

Physical Digestion

  • Breakdown into smaller pieces WITHOUT chemical change
  • Increases surface area for enzyme action
  • Examples:
    • Chewing (mastication) by teeth
    • Mixing with saliva
    • Teeth types and functions:
      • Incisors: Cutting/biting
      • Canines: Tearing
      • Premolars: Crushing
      • Molars: Grinding
    • Stomach role: Churning action mixes food with gastric juices

Teeth Diagrams

Chemical Digestion

  • Breakdown of large insoluble molecules into small soluble ones
  • Carried out by digestive enzymes
  • Allows absorption across membranes
  • Examples:
    • Starch → reducing sugars (amylase)
    • Protein → amino acids (proteases)
    • Fats/oils → fatty acids and glycerol (lipase)

3. Absorption

  • Small soluble molecules pass from digestive tract into bloodstream
  • Main site: Small intestine
  • Most water absorbed from small intestine
  • Some water absorbed from colon (large intestine)

Small Intestine Adaptations

  • Villi: Finger-like projections increasing surface area
  • Microvilli: Even smaller projections on villus cells
  • Rich blood supply: Capillaries absorb nutrients
  • Lacteals: Special lymph vessels absorb fats

Diagram showing villus structure with capillaries and lacteals

4. Assimilation

  • Nutrients transported to cells
  • Cells use nutrients for energy, growth, repair

5. Egestion

  • Removal of undigested food and waste material
  • Occurs through rectum and anus
  • Not the same as excretion (waste removal from cells)

Digestive Enzymes and Functions

Salivary Glands

  • Amylase (saliva)
    • Acts on: Starch
    • Produces: Maltose (reducing sugar)
    • Location: Mouth

Stomach

  • HCl (Hydrochloric acid)
    • Function: Creates acidic environment (pH ~2)
    • Kills bacteria
    • Activates pepsin
  • Pepsin
    • Acts on: Protein
    • Produces: Smaller peptides
    • Location: Stomach

Pancreas

  • Amylase
    • Acts on: Starch
    • Produces: Maltose
    • Location: Small intestine (from pancreas)
  • Proteases
    • Acts on: Protein
    • Produces: Amino acids
    • Location: Small intestine
  • Lipase
    • Acts on: Fats/oils
    • Produces: Fatty acids and glycerol
    • Location: Small intestine

Small Intestine

  • Bile (from liver via gall bladder)
    • Function: Emulsifies fats/oils
    • Breaks large fat droplets into smaller droplets
    • Increases surface area for lipase action
    • Neutralizes gastric acid (important for enzyme function)
  • Brunner’s glands (in upper small intestine)
    • Secrete alkaline mucus
    • Protects intestine lining from acid

Absorption Sites

  • Capillaries: Absorb amino acids, glucose, water-soluble vitamins
  • Lacteals: Absorb fatty acids and glycerol (re-assembled into fats in lymph)

Digestion Process Summary

Carbohydrate Digestion

  1. Mouth: Amylase breaks starch into maltose
  2. Stomach: No carbohydrate digestion (acid environment)
  3. Small Intestine: Amylase completes starch → maltose breakdown
  4. Absorption: Maltose broken to glucose in intestinal wall

Protein Digestion

  1. Mouth: No protein digestion
  2. Stomach: Pepsin breaks proteins into peptides; HCl activates pepsin
  3. Small Intestine: Proteases break peptides into amino acids
  4. Absorption: Amino acids absorbed into bloodstream via capillaries

Fat Digestion

  1. Mouth: No fat digestion
  2. Stomach: Mechanical churning only; emulsification begins
  3. Small Intestine:
    • Bile emulsifies fats (breaks into droplets)
    • Lipase breaks fats into fatty acids and glycerol
  4. Absorption: Fatty acids and glycerol absorbed via lacteals

Glossary

Term Definition
Alimentary canal Tube from mouth to anus where digestion occurs
Associated organs Organs that assist digestion (liver, pancreas, etc.)
Physical digestion Mechanical breakdown without chemical change
Chemical digestion Breakdown by enzymes into smaller molecules
Emulsification Breaking large fat droplets into smaller droplets
Absorption Movement from digestive tract into bloodstream
Villi Finger-like projections increasing absorption surface area
Microvilli Even smaller projections on villi
Lacteals Lymph vessels in villi that absorb fats
Assimilation Use of absorbed nutrients by cells