Lipids

• Types of Lipids


  • Triglycerides
  • Phospholipids
  • Sterols

  
• Lipids


  • The one class of large biological molecules that do not include true polymers
  • The unifying feature of lipids is that they mix poorly, if at all, with water
  • Lipids consist mostly of hydrocarbon regions
  • The most biologically important lipids are fats, phospholipids, and steroids

  
• Triglycerides


  • Fats & Oils
  • Predominate form of fat in foods and major storage form of fat in the body
  • Composed of 3 fatty acids + glycerol

  
• Fatty Acids


  Organic acid (chain of carbons with hydrogens attached) that has an acid group at one end & a methyl group at the other end

  
• Triglyceride formation


  glycerol + 3 fatty acids ® triglyceride + H2O

  
• Fatty Acids


  • Vary in length - affects absorption
  • Vary in saturation - affects cooking & storage properties and health

  
• Saturated Fatty Acids


  • Carbon chains filled with hydrogen atoms (no C=C double bonds)
  • Saturated fats appear solid at room temperature

  
• Unsaturated Fatty Acids


  • Carbon chains lack some hydrogens (>1 C=C double bond)
  • Monounsaturated fats have 1 double bond
  • Polyunsaturated fats have >2 double bonds
  • Unsaturated fats appear liquid at room temperature

  
• Omega-3 and Omega-6 Fatty Acids


  Refer to the position of the double bond nearest the methyl (CH3) end of the carbon chain

  
• Hydrogenation


  • Addition of hydrogen to unsaturated fat
  • Makes fat more solid or firm
  • Protects against oxidation and increases shelf-life
  • Widely used in food industry
• Cis vs Trans Fatty Acids

  • In nature, most double bonds are cis (hydrogens next to double bonds on same side)
  • Partial hydrogenation can convert some double bonds to trans
• Phospholipids


  • Similar to triglycerides but have only 2 fatty acids + choline
  • Functions: part of cell membranes and acts as an emulsifier

  
• Sterols


  • Important part of sex hormones, vitamin D, bile, and adrenal hormones
  • Cholesterol is a type of sterol

  
• Fat Digestion


  1. Hydrolysis of triglycerides into monoglycerides, fatty acids, and glycerol

  2. Lingual lipase in mouth

  3. Gastric lipase in stomach

  4. Pancreatic and intestinal lipases in small intestine

  5. Emulsification by bile in small intestine

  
• Lipoproteins


  • Clusters of lipids and proteins used to transport fat
  • Types: chylomicrons, VLDL, LDL, HDL

  
• Functions of Fats


  • In body: provide energy, insulation & protection, cell membrane constituents
  • In foods: provide energy, flavor, aroma, tenderness, carry fat-soluble vitamins, provide essential fatty acids

  
• Essential Fatty Acids


  • Linoleic (omega-6) and linolenic (omega-3) fatty acids that must be provided in diet
  • Found in plant oils, nuts, seeds, whole grains, and fish
  • Play role in normal growth & development and may prevent diseases

  
• Excess fat intake


  Contributes to obesity, diabetes, cancer, heart disease
• Risks from trans fats, cholesterol, and saturated fats
• Benefits from monounsaturated and polyunsaturated fats, including omega-3 and omega-6 fats
• Dietary Recommendations


  • Limit total fat to <30% of calories
  • Limit cholesterol to <300 mg/day
  • Limit saturated & polyunsaturated fats each to <10% of calories
  • Use all fats in moderation
  • Choose lean meats, skinless poultry, nonfat dairy
  • Choose fish 2-3 times/week
  • Choose monounsaturated fats
  • Limit egg yolks to 3-4/week

  
• Fat Substitutes


  • Carbohydrate-based, protein-based, and fat-based
  • Potential health benefits but also potential side effects