BIOL203 Lesson 5

• Lipids

  Types of lipids: fatty acids, triglycerides, phospholipids, cholesterol
• Digestion and absorption of lipids

  1. Chemical and mechanical digestion in mouth melt along with lingual lipase (enzyme)

  2. Digestion in small intestine with help from accessory organs (liver, gallbladder, pancreas); hormones released by epithelial cells alert accessory organs of the arrival of lipids

  3. Absorption of short and long chain fatty acids
• Lipoproteins

  • Chylomicrons: contain protein triglycerides, phospholipids, free cholesterol and cholesterol bound to fatty acids (non-polar); phospholipids' polar ends face outwards to allow dissolution in water
  • VLDL: very low-density lipoprotein
  • HDL: high-density lipoprotein
  • LDL: low-density lipoprotein
• Lipids are the only form of energy stored for prolonged periods of time in the body
• Fatty acids

  • Short chain: 2-4 carbons
  • Medium chain: 6-12 carbons
  • Long chain: 14-24 carbons
  • Can be straight or bent depending on the presence of double bonds
  • Saturated vs unsaturated
• Essential fatty acids


  Omega-3 and omega-6 fatty acids that cannot be synthesized by the body and must come from the diet
• Trans fats


  Man-made fats created through hydrogenation of unsaturated fats, behave like saturated fats
• Triglycerides


  The most common lipids found in food and the body, made up of 3 fatty acids attached to a glycerol molecule
• Phospholipids


  Diglycerides with a polar phosphate group, major structural components of cell membranes
• Cholesterol


  Found only in animal products, necessary for cell membranes, synthesis of hormones and vitamin D
• Polyunsaturated fats are more prone to rancidity when deep fried due to the double bonds in the fatty acid chains; rancid fat is unhealthy and has potential to damage DNA
• Saturated and monounsaturated fats are more heat stable for deep frying
• Phospholipids act as emulsifiers, allowing lipids to mix with polar molecules
• Cardiovascular disease is the leading cause of death in Canada, caused by inflammation and plaque buildup in blood vessels
• Heart attacks are caused by blockage of coronary arteries, strokes are caused by rupture or blockage of arteries in the brain
• Lifestyle changes like increasing fiber, limiting fat intake, and increasing omega-3 intake can help reduce risk of cardiovascular disease
• Statins are a type of medication that can lower cholesterol by interfering with the liver's ability to produce it
• Why are lipids so important?

  • Play a role in cooking and eating --> enhances flavour
  • Increase absorption of fat-soluble vitamins and phytochemicals (at least 20g of fat to absorb fat-soluble vitamins)
  • Contributes to satiety (feeling of fullness)
  • Fat is a type of connective tissue that supports other tissues
• Visceral fat

  • Covers and protects abdominal organs
  • Too much visceral fat increases the risk of cardiovascular disease
• Subcutaneous fat

  • located below the skin surface, helps maintain body heat and cushion body
• Triglycerides?

  Made up of 3 fatty acids
• Phospholipids?

  Made up of 2 fatty acids
• Cholesterol?

  Does not contain fatty acids; it is not a source of energy)
• Fatty acids (FA)?

  • Chain of C atoms attached to H atoms
  • Left part = methyl group (carbon atom attached to 3 hydrogen atoms)
  • Right part = acid group (for example, carbon atom attached to oxygen by double bond and OH molecule
• Saturated fatty acids

  • No double bonds within carbon chain
• Unsaturated fatty acids

  • Double bonds within carbon chain; one double bond=monounsaturated FA; 2+ double bonds=polyunsaturated FA
• Saturation level of fats depend on their behaviour (for example, butter is solid, but oil is liquid at room temperature)
• Omega-6 family

  • easily reached by diet; linoleic acid converted to arachidonic acid to synthesize cell membrane
• Omega-3 family

  • few foods can supply them
  • Linoleic acid = present in walnuts
  • DHA (docosahexaenoic acid) and EPA (eicosapentaeonic acid) = found in fish
• Use of DHA?

  Essential for brain development, maintenance of normal brain function, improves capacity to learn
• Use of EPA?

  lowers blood pressure, protects against irregular heartbeats, reduces blood clot formation and inflammation
• What are the characteristics of trans fatty acids (TFAs)?

  • 2 shapes depending on if H bonds are on the same side or opposite ends
  • Products with TFAs have longer shelf life
• Triglycerides: most common lipids found in food --> present in 95% of what we eat and composes 99% of body fat; varying amounts of FAs (saturated, monounsaturated or polyunsaturated)

  • MUFAs>PUFAs = increased thickness of oil
• Phospholipids: diglycerides with polar ends attached to 2 non-polar hydrocarbon tails; they are partially soluble; structure:

  • Choline = top part, made of CH molecules attached to a positively charged N
  • Phosphate group = middle part, O atoms attached to P atom
  • Glycerol = bottom part, 3 CH molecules, 2 of them are linked to O atom that is attached to fatty acids
• Bile

  • Released by gallbladder, contains cholesterol, salts and lecithin; it breaks down large lipid globules into smaller bits (micelles)
  • Pancreatic lipase (released by the pancreas) breaks down triglycerides into free FAs and monoglycerides
• Absorption of lipids

  • Short and medium FA chains: cross into epithelial cells, go out the other end and enter blood capillaries directed to liver
  • Long FA chains: cross into epithelial cells; once inside, they are repackaged into what looks like a golf ball (chylomicron) in lacteal vessel (subclavian vein in the thoracic duct)
• What are ways that reduce the risk of CVD?

  • Increase soluble fibre intake (improves enterohepatic circulation)
  • Limit fat intake to the AMDR (20-35% of your diet)
  • Increase omega-3 intake --> they have anti-inflammatory effects on the body (AI=1.6g/day for men, 1.1g/day for women)
• Most of our energy is stored as fat, not glycogen
• Double bonds within the FA chain will bend the chain
• Trans fats appear when the H atoms linked to the C atoms on each side of the bond are on opposite sides; they are man-made through the process of hydrogenation (unsaturated FAs become saturated)