Structure of Triglycerides
- Consist of 3 fatty acid tails bonded to the hydroxyl groups on glycerol head
- Process of bonding is called esterification as water is released to create the ester bond
- Structure of fatty acids is composed of a long chain of carbon atoms surrounded by hydrogen atoms
- Free fatty acids have a carboxyl group and a methyl group at each end
De Esterification and Re-esterification
○ De-esterification: removing a fatty acid
○ Re-esterification: reattaching a fatty acid
Ways Fatty Acids Can Vary
- Number of carbons in the chain
- The extent to which the chain is saturated with Hydrogen
- Shape of the chain(bent or straight)
Number of Carbons in different Length Chains:
- Long chain fatty acids: at least 12 carbons
- Medium chain fatty acids: 6-10 carbons
- Short chain fatty acids less than 6 carbons
Saturation Differences
- Saturated: every carbon in the chain has formed a maximum of 4 bonds(2 to carbons and 2 to hydrogens)
○ Animal products
○ Can stack together neatly and form a solid mass- Unsaturated: Plant products which cant uniformly stack together and therefore remain liquidy
Types of Unsaturated Chains
○ monounsaturated: a single double bond between carbon atoms due to the absence of hydrogen atoms
○ Polyunsaturated: 2 or more double bonds in the carbon chain due to the absence of hydrogen atoms at different locations
Variation in Chain Shape due to bonding patterns of Hydrogens
- Cis fatty acids: the hydrogens attached to the double bonded carbons on the same side
○ How its found naturally - Trans fatty acids: the hydrogens attached to the double bonded carbons zigzag back and forth across the carbon chain
○ Partially hydrogenated made in labs making it stack like saturated fat in our arteries
Systems used to Name Fatty Acids
Omega system: indicates where the first double bond closest to the methyl(omega) end of the chain occurs
- E.g. Linoleic acid is 18:2 omega6, meaning it has 18 carbons, with 2 double bonds and the first double bond starts at the 6th carbon from the omega end
Delta system: indicates where the first double bond closest to the carboxyl(delta) end of the chain is
2 essential fatty acids
- Human body cannot create alpha linolenic acid and linoleic acid
- Therefore they are essential fatty acids which must be supplied through diet
Determining Fatty Acid Family
- Location of double bond closest to the omega end determines the fatty acids family
- E.g. 1st double bond occurs between the 3rd and 4th carbon, it is an omega-3 fatty acid
Sources of Triglycerides
- Saturated Fats: animal products
- long chain: fat in beef, pork, lamb
- med/short chain: milk fat, butter
- Unsaturated fats: plant products
- mono: olive oil, canola oil, peanut oil
- poly: sunflower oil, corn oil, fish oil
- omega 3 Eicosapentaenoic acid: tuna, salmon
- Omega 3: alpha-linolenic acid: walnuts, chia seeds
- omega 6 linoleic acid: beef, chicken eggs
- natural trans fatty acid: milk, meat
Functions of Triglycerides: energy providing
- Provide 9 calories per gram
- Main fuel source for all body cells except the nervous system and red blood cells
- Provide up to 70% of energy during rest or light PA
- Main fuel source for all body cells except the nervous system and red blood cells
Function of Triglycerides: energy storage
- Excess calories from other macronutrients are converted into fatty acids and then to triglycerides
- Triglycerides can be easily stored due to how stable they are and because they can expand 2-3 times their size
○ Adipose cell can increase in weight about 50 times
- Triglycerides can be easily stored due to how stable they are and because they can expand 2-3 times their size
Function of Triglycerides: insulation and protection
- Insulating layer of fat under the skin, subcutaneous fat is made of triglycerides
- Visceral fat surrounds organs protecting them
Functions of Triglycerides: Aid fat soluble vitamin absorption and transport
- Fats in food carry Fat soluble vitamins(ADEK) to the small intestine where dietary fats assist in their absorption
Functions of Essential Fatty Acids
- Eicosanoids have heaps of actions including regulation of:
○ BP
○ Blood clotting
○ Sleep wake cycles
○ Body temperature
○ Inflammation
○ Hypersensitivity
Function of Phospholipids
Emulsifier: a compound which forms a shell around fat droplets so that the droplets can be suspending in water and not clump together
- E.g. bile and lecithins
- Hydrophobic tails reach towards fat droplets, forming the inside of the shell
- the hydrophilic heads extending away from the fat droplet, allowing it to mix with water
- Important for fat to be digested and transported through the bloodstream
Sources of Phospholipids
- Can be either synthesized by the body or supplied through diet
- Lecithins can be found in foods such as:
○ Egg yolks
○ Wheat germ
○ peanuts
- Lecithins can be found in foods such as:
Functions of Sterols
Cholesterol:
- Makes sex hormones
- Makes the active form of vitamin D
- Makes adrenal hormones like cortisone
- Makes bile, an emulsifier
- Part of the cell membrane allowing fat soluble substances to move in and out
Food Sources of Sterol
- Foods of animal origin
○ Meat
○ Fish
○ Poultry
○ Eggs
○ Dairy- 1/3 of cholesterol comes from food while 2/3 is produced by the body
Fat Digestion
- Begins in the mouth where lingual lipase is secreted from the base of the tongue, breaking down triglycerides with short and medium chain fatty acids
- In the stomach gastric lipase breaks down triglycerides into mono, di and free fatty acids
○ Lipid digestion is limited due to it floating on top of the water contents in the stomach - Fat in the small intestine then triggers the release of CCK which stimulates the release of bile, lipase and colipase
○ Bile emulsifies fat and breaks it into many tiny droplets and forms shells around it
○ Increases the surface area of fat and allows pancreatic lipase to break it down into free fatty acids - Phospholipids and cholesterol are also digested in the small intestine by phospholipase and cholesterol esterase
- In the stomach gastric lipase breaks down triglycerides into mono, di and free fatty acids
Fat Absorption
- Lipid portion of micelles is absorbed by brush border of absorptive cells in the Duodenum and Jejunum
- Short and medium chain fatty acids enter the cardiovascular system
- Long chain fatty acids are re-esterified into triglycerides in the absorptive cell before entering the lymphatic circulation
- Bile is re-absorbed and re secreted through enterohepatic circulation
Micelles
water soluble structures formed by emulsifiers surrounding fat droplets
Recommended Fat Intakes
- AMDR is between 20-35% of calories
- less than 10% saturated fat of fat intake
