lipid metabolism

• Lipid Types


  • Triglyceride
  • Phospholipid
  • Fatty acids
  • Sterols/Cholesterol
• Fat in the body

  • Source of concentrated and reserve energy
  • Component of cells
  • Nourish skin, hair
  • Insulation/temperature regulation
  • Protect organs (shock absorber)
• Fat in Food


  • Source of essential fatty acids
  • Provide calories/energy
  • Slows down stomach emptying = satiety
  • Fat-soluble vitamins
  • Aroma, flavor (pick up flavor)
  • Texture
• Triglyceride = TG


  C C C Fatty acid Fatty acid Fatty acid Glycerol backbone + 3 fatty acids
• Types of Fatty Acids

  • Saturated fatty acid
  • Monounsaturated fatty acid
  • Polyunsaturated fatty acid
• Saturated Fat


  • Every carbon is holding every possible hydrogen (i.e. filled to capacity or saturated)
  • Adjacent carbons within fatty acids are linked only by single bonds
  • Saturated fats tend to be solid at room temperature
• Unsaturated Fats


  • Unsaturation = containing fewer hydrogens than the maximum potential (i.e. not saturated with hydrogens)
  • Adjacent carbons are linked by one or more double bonds
  • Unsaturated fats tend to be liquid at room temperature
• The more unsaturated a fat, the more liquid it is at room temperature. The more polyunsaturated the fat is, the sooner it melts.
• Sources and properties


  • Animal foods – saturated fat, solid at room temperature (but fish polyunsaturated)
  • Plant foods – unsaturated, liquid at room temperature (exceptions – palm and coconut oil contain higher saturated than most plants)
• Saturated vs. Unsaturated – Why is it important?

  • Increased hepatic cholesterol synthesis
  • Down-regulation of hepatic LDL receptors
• Physiological Effects of SFA

  • Decreased total cholesterol
  • Decrease LDL
  • No effect on HDL chol.
• Physiological Effects of MUFA

  • Decreases: Total cholesterol, LDL cholesterol, HDL cholesterol
• Physiological Effects of PUFA

  • Oxidizes the Easiest
• Omega nomenclature


  • Carboxyl group
  • Methyl group
• The types Of Fatty Acids

  • Omega-6
  • Omega-3 – highest in cold water fish
• Essential Fatty Acids


  • The body can make all fatty acids except for two: Linoleic acid – omega-6, Linolenic acid – omega-3
  • Deficiency: Poor growth, reproductive failure, vision problems, impaired learning
  • Relatively rare in developed countries
• Omega-3 Fatty Acids


  • Regular consumption of omega-3 fatty acids (EPA, DHA) from fish may protect against some diseases (heart disease, cancer, inflammatory-related)
  • EPA- Eicosapentaenoic acid
  • DHA - Docosahexaenoic acid
• Good Sources of omega 3 fatty acids (EPA, DHA)

  • Cold water fish
  • Walnuts
  • Flax seed
  • Soy bean
• Fish Oil Supplements


  • Excess can increase bleeding/easy bruising and/or gastrointestinal upsets, suppress immune function
  • Some types of fish oil supplements increase the risk of mercury, vitamin A and vitamin D toxicity
• If I am at risk for a heart attack, why is a diet rich in omega 3 fatty acids good for me?

  • Omega 3 fatty acids help prevent blood clots
  • Omega 3 fatty acids improve blood lipids
  • Omega 3 fatty acids lower blood pressure
  • Omega 3 fatty acids modulate inflammatory response
• Eicosanoids


  • Made from fatty acids (20 carbons)
  • Regulate blood pressure, blood clotting, involved in immune response to injury or infections (eg. fever, pain, inflammation)
  • Aspirin work?
  • Eicosanoids are hormone-like but differ from hormones because typically act on own cells (autocrine) and neighboring cells (paracrine) and may have different effects on different cells
• Eicosanoids


  • Prostaglandins
  • Thromboxanes
  • Leukotrienes
• Competition for enzymes


  • Omega 3 Fatty Acid 20:5 omega 3 (EPA)
  • Omega 6 Fatty Acid 18:3 omega 6
  • 20:3 omega 6
  • 20:4 omega 6 (AA)
  • 22:6 omega 3 (DHA)
  • Brain and nervous system development
  • retina
• Omega 6 Fatty acid

  • Prostaglandin E2 (Anti-coagulant, Lower BP, Reduce inflammation)
  • Thromboxane A2 (Aggregatory, ++++ inflammation)
• Omega 3 Fatty Acid


  • Salad Dressings
  • Mayonnaise
  • Safflower oil
  • Sunflower oil
• Fats in Food Modification

  • Improve stability and shelf-life
  • Alter taste and texture
  • Change cooking properties
• Modifications


  • Hydrogenation
  • Anti-oxidants
  • Emulsifiers
• Hydrogenation


  • Hydrogen is added to unsaturated fats
  • Improves shelf-life, taste, cooking properties
  • BUT also increases saturation, and trans fat content
• Polyunsaturated fatty acid undergoes full hydrogenation


  Becomes a Saturated fatty acid
• Polyunsaturated fatty acid undergoes partial hydrogenation

  • Becomes a Partially hydrogenated fatty acid (CIS)
  • Becomes a Partially hydrogenated fatty acid (TRANS)
• Margarine, particularly stick form is high in hydrogenated fats
• Antioxidants


  • Compound that protects other compounds from oxygen by itself reacting with oxygen
  • e.g. BHT, BHA, vitamins C, A, E, phytonutrients
• Emulsifiers


  • A substance that mixes with both fat and water and can break fat globules into small droplets, thereby suspending fat in water
  • Allow fat and water to mix (e.g. mayo, salad dressings)
  • e.g. monoglycerides, diglycerides, Lecithin (a naturally occurring phospholipid – joins fats and water) but no magical health properties
  • Used in margarine, chocolate, salad dressings, and frozen desserts to keep the fats dispersed
• Phospholipids


  • Components of cell membranes
  • Can serve as emulsifiers in the body, joining with both water and fat
  • Widespread in foods
• Sterols


  • Cholesterol
  • Free cholesterol
  • Cholesterol ester
  • Vitamin D
  • Bile acids
• Cholesterol is the most famous (or infamous) lipid
• Lipid transport


  • Lipoprotein
  • Metabolism
• Lipid Digestion and Absorption

  1. Goal of fat digestion: Dismantle triglycerides into components (MGs, fatty acids, and glycerol)

  2. Fat digestion: Salivary lipase, Gastric Lipase, Pancreatic lipase, CCK, Bile, emulsification (surface area, enzyme access)

  3. Directly into bloodstream: Glycerol and short- & medium-chain fatty acids

  4. Lymphatic system: Micelles diffuse into intestinal cells, Reassembly of triglycerides, Packed with proteins – chylomicrons, Bypass liver at first
• Four main types of lipoproteins

  • Chylomicrons
  • Very-low-density lipoproteins (VLDL)
  • Low-density lipoproteins (LDL)
  • High-density lipoproteins (HDL)
• Chylomicrons


  • Largest and least dense
  • Transport diet-derived lipids
  • Liver removes remnants from blood