Food substances and nutrition

• Food provides energy for daily activities and warmth

• Food furnishes raw materials for tissue growth and repair

• Food includes substances to help maintain health

• There are seven essential types of food substances

Energy-Providing Food Substances

• Carbohydrates are a source of energy
• Lipids are a source of energy
• Proteins are a source of energy

Non-Energy-Providing Food Substances

• Minerals are essential to health
• Vitamins are essential to health
• Dietary fibre is essential to health
• Water is essential to health

Carbohydrates

• Includes monosaccharides, disaccharides, and polysaccharides
• Sugars and starch act as the main energy source for body activities
• Glycogen acts as energy reserves
• Cellulose is a source of dietary fibre
• Sources: Fruits, honey, milk, table sugar (for sugars), and rice, wheat, potatoes, taros (for starch)

Lipids

• Triglycerides are the most common type; formed from glycerol and three fatty acids
• Act as energy reserves
• Fat in adipose tissues around internal organs acts as a shock absorber
• Subcutaneous fat acts as a heat insulator
• Involved in the absorption, transport, and storage of lipid-soluble vitamins
• Used to produce hormones
• Phospholipids are major components of cell membranes
• Sources: Fatty meat, seeds, nuts, milk, and dairy products

Proteins

• Consist of one or more polypeptides, formed from the condensation of amino acids
• Used for growth and repair of body tissues
• Used to produce enzymes, antibodies, and some hormones
• Broken down to release energy if carbohydrates and stored fat are used up
• Sources: Meat, fish, eggs, beans, milk, and dairy products

Minerals

• Calcium is a component of bones and teeth
  • Involved in blood clotting, muscle contraction, and sending messages in the nervous system
  • Deficiency leads to rickets
  • Sources: Canned sardines, milk, dairy products, tofu, and some green vegetables
• Iron is a component of haemoglobin
  • Deficiency leads to anaemia
  • Sources: Beef, liver, beans, cabbage, spinach, and raisins

Vitamins

• Vitamin A (lipid-soluble) is needed for the formation of a pigment in the retina
  • Maintains the cornea, skin, linings of the alimentary canal and a healthy breathing system
  • Deficiency leads to night blindness, drying of the cornea, and easy infection of the linings of the lungs and trachea
  • Sources: Fish liver oils, liver, eggs, milk, dairy products, vegetables, and fruits containing carotene
• Vitamin D (lipid-soluble) promotes the absorption of calcium and phosphate
  • Deficiency leads to rickets
  • Sources: Fatty fish, fish liver oils, liver, egg yolks, and is produced by the skin under sunlight
• Vitamin C (water-soluble) is needed for the growth and repair of connective tissues
  • Promotes the absorption of iron, and helps the immune system work properly
  • Deficiency leads to scurvy
  • Sources: Fresh vegetables and fruits

Dietary Fiber

• Helps faeces pass out of the body by adding bulk to food to stimulate peristalsis
• Holding water to make faeces softer
• Deficiency leads to constipation
• Sources: Vegetables, fruits, and wholemeal products

Functions of Water in the Body

• Reactant in chemical reactions
• Medium for chemical reactions
• Medium of transport
• Cooling agent to help regulate body temperature
• Major component of lubricating fluids

Glucose Test

• Used to detect glucose
• Using glucose test paper
• Dip the test end into the food sample and observe for colour changes in the test

Benedict’s Test

• Used to detect reducing sugars (monosaccharides and disaccharides except sucrose)
• Add an equal volume of Benedict’s solution to the food sample; boil the mixture in a water bath for 5 minutes
• A brick-red precipitate indicates a positive result

Iodine Test

• Used to detect starch
• Add iodine solution to the food sample
• A colour change from brown to blue-black indicates a positive result

Grease Spot Test

• Used to detect lipids
• Put a drop of the food sample onto filter paper; observe for a translucent spot after drying
• Immerse the spot in organic solvent; disappearance of the spot indicates a positive result

Protein Test

• Used to detect proteins
• Using a protein test paper
• Dip the test end into the food sample and observe for colour changes in the test

DCPIP Test

• Used to detect Vitamin C
• Add the food sample drop by drop to DCPIP solution with gentle shaking
• Decolourization indicates a positive result

Balanced Diet

• Consists of food substances in the right amounts and proportions based on the food pyramid
• Maintain a balance between energy input and energy output

Food Pyramid Key Components

• Eat Least: Fats, oils, salt, and sugar
• Eat Moderately: Milk and alternatives; Meat, fish, eggs and alternatives
• Eat More: Vegetables, and Fruits
• Eat the most: Grains
• Drink 6–8 glasses of fluid everyday

Factors Affecting Dietary Requirements

• Age: Children need the greatest amount of energy per unit body mass because they have the highest metabolic and growth rate and highest rate of heat loss
  • Children and teenagers need large amounts of proteins, calcium and iron for building body tissues.
• Sex: Males need more energy due to higher metabolic rate, heat loss, larger body size, and more muscle mass.
  • Males need more protein to build and repair muscles.
  • Females need more iron to replace the loss during menstruation.
• Level of activity: More physically active people need more energy for muscular activities
• Body status: Pregnant women need more energy, proteins, and iron for foetus growth and foetal red blood cell formation
  • Breast-feeding mothers need an extra supply of nutrients for milk production

Energy Balance

• Eating too little: energy input is less than energy output, leading to the breakdown of food reserves and weight loss
• Eating too much: energy input is greater than energy output, leading to weight gain; can result in being overweight or obese

Health Risks of Obesity

• Overweight or obese individuals have a higher risk of diabetes mellitus, high blood pressure, heart disease, stroke, and arthritis

Nutrition Labels

• Provides information about energy and nutrient contents
• Reference Amount: Energy and nutrient contents labelled per 100 g, per serving, or per package
• Energy Content: Measured in kilocalories (kcal), Calories (Cal), or kilojoules (kJ)
• Nutrient Contents: Typically lists the amounts of proteins, total fats, saturated fats, trans fats, carbohydrates, sugars, and sodium; other nutrients may also be included

Human Nutrition

• Large, complex food molecules must be broken down because:
  • Cell membranes are differentially permeable: Large molecules can't enter the cells
  • Food molecules are structurally different from the body's own molecules: These must be broken down to build our own molecules
• Nutrition consists of five main processes: Ingestion, digestion, absorption, assimilation, and egestion

Digestive Processes

• Ingestion: Taking food into the body
• Digestion: Breaking down food into smaller molecules
• Absorption: Taking up the smaller molecules into the body
• Assimilation: Using the absorbed molecules for growth, repair, and energy
• Egestion: Eliminating undigested waste

Digestive System

• Nutrition takes place in digestive system
• Consists of the alimentary canal and associated digestive glands

Alimentary Canal

• The alimentary canal is a long, muscular tube: Begins at the mouth and ends at the anus
• Digestive Glands: Produce digestive juices, released into the alimentary canal to aid digestion

Components of the Alimentary Canal

• Mouth cavity
• Pharynx
• Esophagus
• Stomach
• Liver
• Pancreas
• Small intestine
• Duodenum
• Ileum
• Large intestine:
• Caecum
• Appendix
• Colon
• Rectum
• Anus