Health and Diet

• Energy budgets and diet

  An individual’s ‘energy budget’ refers to the amount of energy taken in (i.e. calories consumed) and the amount of energy used. If someone’s energy intake is higher than their energy use, the excess energy is converted to fat and they will put on weight. If their energy intake is less than their energy use, they will burn fat reserves and lose weight.
• Investigating vitamin C content of food


  1. Create a 1 mg cm-3 vitamin C solution

  2. Prepare serial dilutions of 0.5, 0.25, 0.125 and 0.0625 mgcm-3

  3. Measure out a set volume of DCPIP using a measuring cylinder and pour into a test tube

  4. Dropwise, add vitamin C solution to the test tube and gently shake for 30 seconds

  5. Keep adding drops of the vitamin solution and shaking until the blue colour disappears

  6. Record the number of drops added to cause the colour change

  7. Repeat twice more with each vitamin C concentration and calculate a mean

  8. Repeat with serial dilutions

  9. Draw a graph showing volume of vitamin C solution against concentration and connect data points with a curve of best fit

  10. Test your unknown solution using the method above and use the calibration curve to determine its concentration
• DCPIP


  A molecule that changes from blue to colourless in the presence of vitamin C
• Calibration curve


  • Graph showing volume of vitamin C solution against concentration with a curve of best fit
• Control variables

  • Temperature
  • Volume of DCPIP
  • Time spent shaking the solution
• Carbohydrates

  Carbohydrates are long chains of sugar molecules (the technical term is ‘polysaccharides’) formed from lots of individual sugar molecules (monosaccharides) joining together. When two monosaccharides react to form a disaccharide, a condensation reaction occurs. During the condensation reaction, a molecule of water is removed (from a hydroxyl group on one sugar and a hydrogen on another) and a glycosidic bond forms. When polysaccharides are broken down during digestion, a hydrolysis reaction occurs in which a water molecule is added to break the glycosidic bond.
• Carbohydrates:

  
• Polysaccharides found in plants


  • Starch
  • Cellulose
• Starch


  Broken down by the plant when it needs energy
• Cellulose


  Major component of plant cell walls
• Starch


  Exists in two different forms: amylose and amylopectin
• Amylose


  Unbranched spiralling chains of alpha-glucose molecules, very compact so lots can be packed into a cell
• Amylopectin


  Branched chains of alpha-glucose molecules, increased surface area means enzymes can quickly break it apart when glucose is needed for respiration
• Cellulose


  Long unbranched chains of beta-glucose molecules, multiple chains linked by hydrogen bonding to form strong microfibrils that give plant cells shape and structural support
• Glycogen


  Branched chains of alpha glucose, similar to amylopectin but with more side-branches, giving it a large surface area for enzyme action to release glucose when energy is needed, more compact than amylopectin so more can be stored in a cell
• In animals, the energy storage carbohydrate is glycogen
• Types of lipid


  • Triglycerides
  • Phospholipids
  • Cholesterol
• Triglycerides and phospholipids


  • Similar structures as they are both made up of glycerol connected to fatty acids molecules through ester bonds
  • Triglycerides contains three fatty acid 'tails' whereas phospholipids only have two
  • Phospholipids also possess a phosphate group which is absent in triglycerides
• Saturated fatty acid


  Only single carbon-carbon bonds
• Unsaturated fatty acid


  Contains at least one double carbon bond
• A diet high in saturated fat


  Increases the risk of CVD because it increases blood cholesterol levels
• Synthesis of a phospholipid or triglyceride from glycerol and fatty acids

  1. Formation of an ester bond

  2. Release of a water molecule (condensation reaction)
• Breaking apart a triglyceride or phospholipid


  Addition of water (hydrolysis reaction)
• Lipids:

  
• Different types of lipids and their functions


  • Triglycerides
  • Phospholipids
  • Cholesterol
• Triglycerides


  Used as an energy store, a lot of energy is released when the ester bonds are hydrolysed - around twice as much compared to the breakdown of carbohydrates, group together into lipid droplets where the hydrophobic tails face inwards and the hydrophilic heads face outwards, insoluble droplets make good energy storage molecules since they do not affect the osmotic potential of the cell
• Phospholipids


  Main component of cell membranes, form a phospholipid bilayer with the hydrophobic tails facing each other and the hydrophilic heads facing outwards, forming a barrier to prevent any polar molecules from entering or leaving the cell
• Cholesterol


  Found in cell membranes, helps to strengthen the membrane by pushing the hydrophobic tails of phospholipids closer together, making the membrane more rigid
• Saturated fats


  • Contain only single C-C bonds
  • Found in animal-based foods such as cheeses, butter and beef burgers
  • Unhealthier
• Unsaturated fats


  • Contain at least one double C=C bond
  • Found in plant-based foods such as olive oil, nuts and oily fish
  • Healthier
• Saturated fats


  Increase the levels of low-density lipoprotein (LDL) in the blood
• Lipoproteins


  Little packages of lipids surrounded by protein that function to transfer cholesterol between the liver and body tissues
• LDLs


  Take cholesterol from the liver and deposit it in the blood, where it will circulate until it is needed by our cells
• HDLs


  Transport cholesterol from the bloodstream and return it to the liver where it can be destroyed
• High intake of unsaturated fats


  Increases HDL levels in our blood
• High amount of LDLs and low levels of HDLs


  Can increase cholesterol levels, making us more susceptible to cardiovascular disease
• Our cells need cholesterol because it is used to make sex-hormones, to synthesise bile and as a component of plasma membranes
• Our liver already synthesises enough cholesterol, then on top of that we consume way more than our bodies know what to do with
• It is important that we have a high ratio of HDL to LDLs by eating more unsaturated fats to saturated fats
• High levels of HDLs will ensure that excess cholesterol is taken back to the liver to be broken down and removed from our body