Human nutrition

• Biological molecules


  Things like carbohydrates, lipids and proteins. They're generally long, complex molecules made up from smaller basic units.
• Carbohydrates


  • Made up of the elements carbon, hydrogen and oxygen
  • Starch and glycogen are large, complex carbohydrates made up of many smaller units like glucose or maltose joined in a long chain
• Simple sugars


  • Maltose
  • Glucose
• Proteins


  • Made up of long chains of amino acids
  • Contain carbon, nitrogen, hydrogen and oxygen atoms
• Lipids


  • Built from fatty acids and glycerol
  • Contain carbon, hydrogen and oxygen atoms
• Before a food test

  1. Get a piece of food

  2. Break it up using a pestle and mortar

  3. Transfer to a beaker and add distilled water

  4. Stir with a glass rod to dissolve some of the food

  5. Filter the solution using a funnel lined with filter paper to get rid of solid bits
• Use the Benedict's Test to Test for Glucose


  1. Prepare a food sample and transfer 5 cm³ to a test tube

  2. Prepare a water bath so that it's set to 75 °C

  3. Add some Benedict's solution to the test tube (about 10 drops) using a pipette

  4. Place the test tube in the water bath using a test tube holder and leave it in there for 5 minutes

  5. If the food sample contains glucose, the solution in the test tube will change from its normal blue colour. It will become green or yellow in low concentrations of glucose, or brick-red in high concentrations of glucose
• Glucose is found in all sorts of foods such as biscuits, cereal and bread
• Always use an excess of Benedict's solution - this makes sure that all the glucose reacts
• Use Iodine Solution to Test for Starch


  1. Make a food sample and transfer 5 cm³ of your sample to a test tube

  2. Then add a few drops of iodine solution and gently shake the tube to mix the contents

  3. If the sample contains starch, the colour of the solution will change from browny-orange to black or blue-black
• Foods like pasta, rice and potatoes contain a lot of starch
• Use the Biuret Test to Test for Proteins

  1. Prepare a sample of your food and transfer 2 cm³ of your sample to a test tube

  2. Add 2 cm³ of biuret solution to the sample and mix the contents of the tube by gently shaking

  3. If the food sample contains protein, the solution will change from blue to pink or purple. If no protein is present, the solution will stay blue
• Meat and cheese are protein rich and good foods to use in this test
• Use the Sudan III Test to Test for Lipids


  1. Prepare a sample of the food you're testing (but you don't need to filter it). Transfer about 5 cm³ into a test tube

  2. Use a pipette to add 3 drops of Sudan III stain solution to the test tube and gently shake the tube

  3. If the sample contains lipids, the mixture will separate out into two layers. The top layer will be bright red. If no lipids are present, no separate red layer will form at the top of the liquid
• Lipids are found in foods such as olive oil, margarine and milk
• Nutrients


  • Carbohydrates
  • Lipids (fats and oils)
  • Proteins
  • Vitamins
  • Mineral ions
  • Water
  • Dietary fibre
• Carbohydrates


  Found in pasta, rice, sugar
• Lipids (fats and oils)


  Found in butter, oily fish
• Proteins


  Found in meat, fish
• Vitamins A


  Found in liver
• Vitamins C


  Found in fruit, e.g. oranges
• Vitamins D


  Found in eggs
• Mineral ions - Iron


  Found in red meat
• Mineral ions - Calcium


  Found in milk, cheese
• Water


  Found in food and drink
• Dietary fibre


  Found in wholemeal bread, fruit
• Carbohydrates


  • Provide energy
• Lipids (fats and oils)


  • Provide energy, act as an energy store and provide insulation
• Proteins


  • Needed for growth and repair of tissue, and to provide energy in emergencies
• Vitamins A


  • Helps to improve vision and keep your skin and hair healthy
• Vitamins C


  • Needed to prevent scurvy
• Vitamins D


  • Needed for calcium absorption
• Mineral ions - Iron


  • Needed to make haemoglobin for healthy blood
• Mineral ions - Calcium


  • Needed to make bones and teeth
• Water


  • Just about every bodily function relies on water- we need a constant supply to replace water lost through urinating, breathing and sweating
• Dietary fibre


  • Aids the movement of food through the gut
• A balanced diet gives you all the essential nutrients you need -in the right proportions
• Essential nutrients


  • Carbohydrates
  • Proteins
  • Lipids
  • Vitamins
  • Minerals
  • Water
  • Fibre
• You get energy from the food you eat, but the amount of energy you need isn't a set thing- it's different for everyone
• Energy requirements


  • Activity level
  • Age
  • Pregnancy