Fatty Acid

Aka: Fatty Acid, Dietary Fat, Cooking Oil, Unsaturated Fatty Acid, Saturated Fatty Acid, Monounsaturated Fatty Acid, Essential Fatty Acid, Dietary Fatty Acid, Fatty Acid Metabolism

1. See Also
   1. Omega-3 Fatty Acid
   2. Omega-6 Fatty Acid
   3. Lipid
   4. Triglyceride
   5. Cholesterol
2. Definitions
   1. Lipid
      1. Organic molecules containing Hydrocarbons
      2. Poorly soluble in water, but soluble in organic solvents
      3. Examples include free Fatty Acids, Triglycerides, phospholipids
   2. Fatty Acids
      1. Aliphatic hydrocarbon chain with a terminal COOH group
      2. Chains vary in length of 6 to 30 carbons (even numbers, sythesized and broken down in 2 carbon increments)
      3. Major component of fats, with Triglycerides composed of 3 Fatty Acid chains linked to a gylcerol molecule
      4. Fatty Acids may be saturated, monounsaturated or polyunsaturated
   3. Saturated Fatty Acids
      1. Saturated with hydrogen atoms and contain only single bonds between carbons
      2. Palmitic Acid (16 carbons) to stearic Acid (18 carbons) are common saturated fats in humans
   4. Monounsaturated Fatty Acids
      1. Carbon chain with a single pair of missing hydrogens (1 double bond)
      2. Oleic Acid (e.g. Olive oil) is a 18 carbon chain
   5. Polyunsaturated Fatty Acids
      1. Carbon chain with more than 1 pair of missing hydrogens (more than 1 double bond)
      2. Linoleic Acid (e.g. Safflower oil) and Linolenic Acid (e.g. Soybean oil) each are 18 carbon chains
   6. Essential Fatty Acids
      1. Long chain Fatty Acids (18 carbon chains) that cannot be synthesized in humans (specific double bond locations)
      2. Examples include Linoleic Acid and linolenic acid
   7. Triglyceride
      1. Lipid composed of three molecules of Fatty Acid esterified to glycerol
      2. Triglycerides are a non-polar fat synthesized from Carbohydrates or ingested
      3. Triglycerides are High Energy Molecules that are stored for later use in animal adipose cells (fat cells)
   8. Diglyceride
      1. Lipid composed of two Fatty Acid chains esterified to glycerol
   9. Monoglyceride
      1. Lipid composed of a single Fatty Acid chain esterified to glycerol
   10. Phosphoglyceride
       1. Diglyceride with the one free OH group on glycerol attached to a phosphate (Phosphatidate)
       2. Phosphate in turn is attached to serine, Ethanolamine, choline or Inositol
       3. Includes Phosphatidyl Serine, Phosphatidyl Ethanolamine, Phosphatidyl choline, Phosphatidyl Inositol
3. Physiology: Fatty Acid Metabolism
   1. 
   2. Fatty Acids are stored for later energy use, bound to glycerol, as Triglycerides
      1. Insulin promotes Fatty Acid and Triglyceride synthesis (as well as that of glycogen and Proteins)
      2. Insulin promotes fat cell uptake of Glucose, which may be used to synthesize Fatty Acids
      3. Fatty Acids are synthesized by adding, in repeated cycles, 2 carbon atoms (from acetyl CoA) at a time
      4. Three Fatty Acid chains in turn, are bound to one glycerol to form Triglycerides which are stored in fat cells
      5. Insulin reduces fat cell intracellular cAMP, thereby reducing Lipase activity (and Triglyceride breakdown)
   3. Fatty Acids are burned as fuel in the Kreb Cycle (TCA Cycle)
      1. Hypoglycemia triggers ephinephrine, Norepinephrine and Glucagon release
      2. Ephinephrine, Norepinephrine and Glucagon bind cell receptors, trigger cAMP to activate Lipase within fat cells
      3. Lipase breaks down Triglyceride into its glycerol backbone and three Fatty Acid chains
      4. Fatty Acids are degraded (oxidized) by removing, in repeated cycles, 2 carbon atoms at a time (acetyl CoA)
      5. Glycerol may also enter Glycolysis (via Glycerol-3P to Dihydroxyacetone Phosphate to Glyceraldehyde-3P)
      6. Energy from each extracted acetyl coA enters the Kreb Cycle
      7. Each Kreb Cycle generates NADH and FADH2 (total energy 17 ATP per Fatty Acid chain)
   4. Fats offer high energy stores (9 KCals/g) compared with Carbohydrates and Proteins (4 kcals/g)
      1. Triglycerides are non-polar and bind less water (more compact than Carbohydrates, Proteins)
      2. Each triglcyeride contains 3 Fatty Acids, each with 16 to 18 carbons (fueling 24-27 Kreb Cycles)
      3. In addition, glycerol, the Triglyceride backbone, may also fuel Glycolysis and the Kreb Cycle
   5. Fatty Acid Metabolism may also yield Ketones
      1. 
      2. Fatty Acid chains are broken down into multiple acetyl-CoA molecules and a final acetoacetyl CoA
      3. Acetoacetyl CoA may be further broken down into acetyl-CoA for the Kreb Cycle or converted to Ketones
      4. Ketones include Acetoacetate, acetone and hydroxybutyrate
      5. Ketones may be used as fuel by the brain, heart and Muscle
      6. Ketones are typically generated at times of starvation or with Insulin deficiency (Diabetic Ketoacidosis)
4. Approach: Oils
   1. Use olive oil in non-high heat preparation (cold salads, roasting)
   2. Safflower oil, canola oil and peanut oil are safer oils for cooking, able to withstand high heat
5. Types: Saturated Fatty Acid
   1. Carbon chain with a maximum number of attached hydrogens (no double bonds)
   2. Risks
      1. Increases LDL Cholesterol (esp. long chain Fatty Acids with >10 carbons)
      2. Increased Coronary Artery Disease risk
   3. Examples
      1. Palmitic Acid (e.g. Palm oil): 16 carbon chain
      2. Stearic Acid (e.g. Animal fat): 18 carbon chain
6. Types: Monounsaturated Fatty Acids
   1. Carbon chain with a single pair of missing hydrogens (1 double bond)
   2. Benefits
      1. Decreased risk of cardiovascular disease
      2. Lowers LDL Cholesterol
   3. Examples
      1. Oleic Acid (e.g. Olive oil): 18 carbon chain
7. Types: Polyunsaturated Fatty Acids
   1. Carbon chain with more than 1 pair of missing hydrogens (more than 1 double bond)
   2. Benefits
      1. Specific to Omega-3 Fatty Acids (sub-type of polyunsaturated fats)
   3. Risks
      1. Increased weight gain
      2. Gallstone formation
   4. Examples
      1. Linoleic Acid (e.g. Safflower oil): 18 carbon chain (Essential Fatty Acid)
      2. Linolenic Acid (e.g. Soybean oil): 18 carbon chain (Essential Fatty Acid)
      3. Arachidonic Acid (e.g. Meat and dairy products): 20 carbon chain (Essential Fatty Acid)
      4. Eicosapentaenoic Acid (e.g. Fish Oil): 20 carbon chain (Essential Fatty Acid)
      5. Docosahexaenoic Acid (e.g. Fish Oil): 22 carbon chain (Essential Fatty Acid)
8. Types: Trans-Fatty Acids
   1. Double bond of unsaturated fat is in trans-configuration
      1. Hydrogens are on opposite sides of the double bonds
      2. Contrast with cis-configuration where the hydrogens are on same side of the bond
   2. Synthesized via hydrogenation (artificial addition of hydrogens)
      1. Converts liquid vegetable oils to semi-solids or solid fats
   3. Risks
      1. Directly associated with increased risk of heart disease
      2. Increase LDL Cholesterol and Serum Triglycerides
      3. Decreases HDL Cholesterol
   4. Examples
      1. Elaidic Acid (e.g. margarines): 18 carbon chain (this is the trans form of oleic acid)
9. Prevention: Dietary Recommendations
   1. Keep Fatty Acid intake less than 30% of total daily calories
   2. Limit saturated fat to less than 7% of total daily calories
   3. Limit trans-fats to less than 1% of total daily calories
10. References
    1. Goldberg (2001) Clinical Biochemistry, Medmasters, Miami, p. 17-23
    2. Guyton and Hall (2006) Medical Physiology, 7th Ed, Elsevier Saunders, Philadelphia, p. 829-58
    3. Hu (2001) J Am Coll Nutr 20(1): 5-19 [PubMed]
    4. White (2009) Am Fam Physician 80(4): 345-50 [PubMed]