Lipids

Background

• Don’t readily dissolve in water (why? The bonds between glycerol and fatty acids causes hydrophobic condition)
  
• Three classes: triglycerides, phospholipids, and sterols
• Each class is composed of fatty acids
  
• Fatty Acids
  • Composed of long chain of carbons with hydrogen atoms bonded to each carbon
  • Chain length varies (6-21 carbons long)
    
  • At one end (alpha end) is an acid  (carboxyl group)
  • At other end (omega end) is a methyl group
  • May be saturated (containing no double bonds) or unsaturated (contain double bond)
    • Saturated fatty acids are linear and melt at higher temps
      • Examples: Myristic acid (coconut oil), palmitic acid (palm oil), and stearic acid (animal and plant fat, most common)
    • Unsaturated fatty acids have a kinked shape and melt at lower temps
      • MUFAs – one double bond
        • Oleic acid most common (found in olive oil)
      • PUFAs – two or more double bonds
        • Linoleic acid (LA, high amounts found in safflower, sunflower, poppyseed, grape seed, corn and cottenseed oils)
          
        • Alpha-linolenic acid (ALA, high amounts in flax, walnut, ligonberry, and hemp seeds)
          
        • Arachidonic acid (ARA, synthesized from LA)
        • Eicosapentanoic acid (EPA, synthesized from ALA)
        • Docosahexanoic acid (DHA, synthesized from ALA)
      • Cis and trans (unsaturated) fatty acids
        • Cis configuration, liquid at room temp
        • Trans configuration, result of partial hydrogenation, semisolid to solid at room temp, increases shelf life
        • FDA test results
          • Trans fatty acids raise LDL levels and may lower HDL levels – causing increased risk to coronary heart disease – nearly equivalent to saturated fatty acids
          • Therefore, CIS fats better!
• Essential Fatty Acids
  • Fatty acids that must be supplied by the diet to maintain health
  • Alpha-linolenic acid (omega-3 fatty acid) and linoleic acid (omega-6 fatty acid) have been identified as essential fatty acids
    • They have important roles in immune function and vision, help form cell membranes, and produce hormone-like compounds called eicosanoids
    • The body has no means to produce double bonds between any carbon atoms from the first to the ninth carbon
    • Omega-3 sources: oily fish, flax, hemp, black raspberry, kiwi, and pecans
    • Omega-6 sources: eggs, avocado, vegetable oils, pumpkin seeds, cashews, pecans, pine nuts, and walnuts
      
  • Alpha-linolenic acid and linoleic acid are precursors to eicosanoids
    • Alpha-linolenic acid is used to derive
      • Eicosapentoic acid (EPA) - serves as a precursor to prostagandins, thromboxans, prostacyclins, and leukotriens (all involved in inflammation)
        
      • Docosahexaenoic acid (DHA) - used in both retina and brain development as well as maintenance
        
    • Linoleic acid is used to derive
      • Dihomo-gamma-linolenic acid (DGLA) - alternate form of linoleic acid, involved in anti-inflammatory and antithromotic mechanisms
        
      • Arachidonic acid (ARA) - involved in cell signaling and vasodilation

Question: what are omega-9 fatty acids?

Omega-9 fatty acids can be synthesized in the body! Examples of dietary omega-9 fatty acids include oleic acid (olive and peanut oil) and erucic acid (wallflower and mustard seeds)

Triglycerides

• Composed of glycerol and three fatty acids
• Fatty acids are bonded to glycerol by esterification
• Deesterification of a triglyceride produces di and monoglycerides
• Enzymes in small intestine breakdown triglycerides into free fatty acids and monoglycerides which are absorbed
• Free fatty acids and monoglycerides undergo reesterification and produce triglycerides that the body needs
• Triglycerides in diet and stored in adipose cells provide energy (9 kcal/g)
• Principle lipid stored
• Insulate the body under skin
• Aids in the transportation of fat-soluble vitamins (A, D, E, K)

Phospholipids

• Composed of glycerol, two fatty acids, and phosphorus-containing compound
• Example of various phospholipids are lecithins which aid in fat digestion by acting as an emulsifier
• Main component of cell membranes

Sterols

• Multi-ringed structure that doesn’t look like other lipids but yet doesn’t dissolve in water
• Cholesterol is a principle example
• Cholesterol
  • Used to synthesize some hormones
  • Precursor to bile acids used in fat digestion
  • Essential component to cell membranes
  • Made by the body and is consumed in the diet

Question: Is there an RDA for lipids/fats? NO

Fat Digestion and Absorption

• Little or no digestions occurs until fats are in the small intestine
• Lecithins and Bile acids (from liver) and enzymes (lipases) from the pancreas digest fats
• Monoglycerides and free fatty acids are absorbed through the intestinal membrane
• Short and medium chained fatty acids are shuttled into the circulatory system
• Long chained fatty acids and monoglycerides are recombined to make triglycerides
• In cells of the intestine, triglycerides aggregate and are combined with cholesterol, protein, and phospholipids to form chylomicrons (lipoprotein particle)
• Chylomicrons exit cell via exocytosis, then taken up by lacteals (lymphatic system) in enterocytes

Fat Transportation

• Chylomicrons are lipoprotein particles surrounded by a thin layer of phospholipids, cholesterol, and protein
  • Thin layer allows for transport in water-based blood
  • Once in blood, triglycerides in chylomicron are broken down by the enzyme, lipoprotein lipase, which is located in blood vessel walls
  • Fatty acids and glycerol are released into bloodstream and taken up by body cells
  • Remnants of the chylomicron are brought to liver
• VLDL – very low density lipoproteins – lipoprotein created in the liver that carries cholesterol and lipids newly synthesized by the liver
  • Once in blood, triglycerides in VLDL are broken down by the enzyme, lipoprotein lipase, which is located in blood vessel walls
  • Because fats are less dense than water, VLDL becomes much heavier and proportionately denser as triglycerides are released
  • The denser VLDL is then termed LDL
  • Most LDL is taken up by receptors on liver cells but some LDL can be taken up by body cells and blood vessel cells
  • Blood vessels cell prevent (by oxidizing) LDL to reenter the blood stream – cholesterol builds up in the cells as well as inner blood vessel walls and over time forms plaque
• HDL – high density lipiproteins – higher proportion of protein – produced by intestine and liver
  • Picks up cholesterol from dead or dying cells and donates the cholesterol to lipoproteins for transport back to the liver
  • It may also block oxidation of LDL
  • Therefore HDL slows the development of cardiovascular disease
    

Question: what is considered a normal lipid panel (or profile)?

Fat Replacements/Substitutes

• Water – addition of water, product contains less fat per serving
• Carbohydrate based (cellulose, Z-trim, Maltrin, Stellar, and Oatrim) – bind water and thicken product to give the “feel” of fat
• Protein based (Simplesse) – protein globules give food the “feel” of fat
• Fat based (Olestra and Salatrim) – linking fatty acids with sucrose

Cardiovascular Disease

• Atherosclerosis
• Myocardial Infarction
• Cerebrovascular accident
• Hypertension
• Hyperlipidemia
• Familial Hypercholesteremia