Human nutrition

• Biological molecules


  Things like carbohydrates and proteins, generally complex made up from smaller units
• You need to know the structure of carbohydrates, lipids and proteins
• Carbohydrates


  Made up of simple sugars
• Carbohydrates


  • Contain the elements carbon, hydrogen and oxygen
  • Starch and maltose are complex carbohydrates made up of many smaller molecules joined together in a long chain
• Proteins


  Made up of amino acids
• Proteins


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


  Made up of fatty acids and glycerol
• Lipids


  • Contain carbon, hydrogen and oxygen
• Preparing a food sample

  1. Get a piece of food and break it up using a mortar and pestle

  2. Transfer the ground up food to a beaker and add some distilled water

  3. Stir the mixture with a glass rod to extract some of the food

  4. Filter the solution using a funnel lined with filter paper to get rid of the solid bits of food
• It's important to remember what carbohydrates, proteins and lipids are made up of
• Use the Benedict's test to test for glucose
• Benedict's test for glucose


  1. Prepare food sample and heat to 25°C

  2. Add Benedict's solution to the test tube

  3. Place the test tube in a water bath and leave for 5 minutes

  4. If the food sample contains glucose, the solution in the test tube will change colour from blue to green, yellow or brick red
• Use iodine solution to test for starch
• Iodine test for starch


  1. Make a sample of the food and transfer it to a test tube

  2. Add a few drops of iodine solution and gently shake the tube

  3. If the sample contains starch, the colour of the solution will change from yellow-orange to black or blue-black
• Use the Biuret test to test for proteins
• Biuret test for proteins

  1. Take a sample of the food and transfer it to a test tube

  2. Add Biuret solution to the sample and mix the contents

  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.
• Use the Sudan III test to test for lipids
• Sudan III test for lipids

  1. Prepare a sample of the food you're testing

  2. Transfer the sample to a test tube

  3. Add drops of Sudan III solution to the test tube and gently shake

  4. If the sample contains lipids, a red layer will separate out at the top of the liquid. If no lipids are present, no separate red layer will form.
• A balanced diet supplies all your essential nutrients
• Essential nutrients

  • Carbohydrates
  • Proteins
  • Lipids
  • Vitamins
  • Minerals
  • Water
• Dietary fibre aids the movement of food through the gut
• Energy requirements


  Vary based on activity level, age, and pregnancy
• Burning food to measure energy content


  1. Obtain a dry food sample and skewer it on a mounted needle

  2. Heat water in a boiling tube

  3. Measure the initial temperature of the water

  4. Hold the burning food under the boiling tube and relight if needed

  5. Measure the final temperature of the water
• Calculating energy content of food


  Energy in Joules = Mass of water x Temperature change x 4.2

  Energy per gram of food = Energy in Joules / Mass of food
• Accuracy of the energy measurement can be improved by minimizing heat loss
• Enzymes


  Used in digestion, produced by specialised cells and released into the gut
• Digestive enzymes


  Break down large molecules into smaller, more absorbable ones
• Digestion of starch and proteins


  Amylase converts starch to maltose and glucose

  Proteases convert proteins to amino acids
• Bile


  Neutralizes stomach acid and emulsifies fats
• Peristalsis


  The muscle contractions that move food through the gut
• The alimentary canal runs through the body
• Parts of the alimentary canal


  • Mouth
  • Oesophagus
  • Stomach
  • Small intestine (duodenum and ileum)
  • Large intestine
  • Rectum
• Small intestine


  • Covered in villi to increase surface area for absorption
  • Each villus has microvilli to further increase surface area