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LIPIDS

LIPIDS. Learning Objectives: Understand lipid terminology and classifications Understand the digestion and absorption of lipids Learn about the function of lipids in the diet, and how they relate to health issues. WHAT ARE THE LIPIDS?.

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LIPIDS

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  1. LIPIDS Learning Objectives: • Understand lipid terminology and classifications • Understand the digestion and absorption of lipids • Learn about the function of lipids in the diet, and how they relate to health issues

  2. WHAT ARE THE LIPIDS? • A broad range of organic compounds that dissolve easily in organic solvents, but range in their solubility in water • Hydrophobic – “water-fearing” • Lipophilic – “fat-loving”

  3. CLASSES of LIPIDS SIMPLE LIPIDS • Fatty Acids • Triglycerides • Waxes COMPOUND LIPIDS • Phospholipids DERIVED LIPIDS • Sterols

  4. FATTY ACIDS • Key building blocks for lipids • Chains of carbon atoms with a carboxyl group at one end, and a methyl group at the other • May be “free” or attached to another compound • Determine the characteristics of the fat

  5. FATTY ACIDS CHAIN LENGTH • Short chain = less than 6 carbons • Medium chain = 6-10 carbons • Long chain = 12 or more carbons • The shorter the carbon chain, the more liquid the fatty acid is

  6. FATTY ACIDS SATURATION • SATURATED FATTY ACID =If all the carbon atoms in the chain are joined with single bonds, and the remaining bonds are attached to hydrogen

  7. FATTY ACIDS SATURATION • UNSATURATED FATTY ACID = If adjoining carbons are joined by double bonds

  8. FATTY ACIDS UNSATURATED • One double bond = monounsaturated fatty acid • Two or more double bonds = poly- unsaturated fatty acid

  9. FATTY ACIDS • Long-chain saturated fatty acids stack tightly and form solids at room temperature • Monounsaturated and polyunsaturated fatty acids don’t stack compactly and are liquid at room temperature • Short-chain saturated fatty acids are also liquid at room temperature • Figure 5.6

  10. FATTY ACIDS TWO TYPES OF BOND FORMATION: • CIS - hydrogens on the carbons joined by a double bond are on the same side = the carbon chain is bent • TRANS – hydrogens on the carbons joined by a double bond are on the opposite side = the carbon chain is straighter

  11. FATTY ACIDS • Omega-3 Fatty Acid – double bond at carbon 3 • Omega-6 Fatty Acid – double bond at carbon 6 • Omega-9 Fatty Acid – double bond at carbon 9 • *count carbons from the methyl (omega) end

  12. Omega 3 • Omega 6 • Omega 9

  13. FATTY ACIDS NOMENCLATURE • Alpha and Omega • 18:0, 18:1, etc.

  14. FATTY ACIDS • Nonessential Fatty Acids – our body can make certain fatty acids so they are not required in the diet • Essential Fatty Acids – our bodies cannot make C-C double bonds before the 9th carbon from the methyl end, so we must get these fatty acids from our diet • EFAS = omega-6 linoleic acid & omega-3 alpha-linolenic acid

  15. FATTY ACIDS • Omega-3: Alpha-Linolenic Acid (ALA), Eicosapentaenoic Acid (EPA), Docosahexaenoic Acid (DHA) • Omega-6: Linoleic Acid, Arachidonic Acid

  16. Sources of Omega-3 Fatty Acids • Flaxseed, soybean oil, walnuts, some leafy dark green vegetables (ALA) • Fatty fish: salmon, tuna, and mackerel, fish oils (EPA and DHA)

  17. Sources of Omega-6 Fatty Acids • Seeds, nuts, common vegetable oils: corn, safflower, cottonseed, sunflower seed, peanut (linoleic acid) • Meat (arachidonic acid)

  18. FATTY ACIDS EICOSANOIDS • A small percentage of fatty acids become eicosanoids • They contain 20 or more carbons and are important in the inflammatory process, blood vessel dilation and constriction, and blood clotting

  19. EICOSANOIDS Omega-6s • Linoleic acid is converted to arachidonic acid and eicosanoids are formed. • Overall effect: constricting blood vessels, promoting inflammation and blood clotting

  20. EICOSANOIDS Omega-3s • Alpha-linolenic acid is converted to eicosapentanoic acid (EPA) and docosahexanoic acid (DHA) and eicosanoids are formed • Overall effect: dilating blood vessels, discouraging blood clotting, and reducing inflammation

  21. TRIGLYCERIDES STRUCTURE • Triglyceride - three fatty acids attached to a glycerol backbone • Diglyceride – two fatty acids +glycerol • Monoglyceride – one fatty acid +glycerol

  22. Triglyceride Fatty Acids

  23. TRIGLYCERIDES FUNCTIONS • Major lipid in the body and diet • Stored fat provides about 60% of the body’s resting energy needs – compactly! • Insulation and protection • Carrier of fat-soluble compounds • Sensory qualities – flavor and texture

  24. Compound Lipids: PHOSPHOLIPIDS • Contain a glycerol bonded to two fatty acids • The phosphate group is hydrophilic while the fatty acids groups are lipophilic • Because of this structure, phospholipids are ideal emulsifiers, and the perfect structure for cell membranes

  25. Functions Cell Membranes • Phosholipids are the major component of cell membranes • Fatty acids, choline, as well as other substances are bound in the phospholipid layer Lipid Transport • In the stomach • In the intestine • In the bloodstream, and the lymphatic system

  26. Protein Channel • Hydrophilic • Hydrophobic • Hydrophilic

  27. Functions Emulsifiers Lecithins are used by the food industry to: • Combine foods that wouldn’t normally mix • Increase dispersion and reduce fat separation • Increase shelf-life, prolong flavor release, and prevent such products as gum from sticking to teeth

  28. Phospholipids in Foods • A typical diet contains only about 2 grams per day • Lecithin (phosphatidylcholine) is the major phospholipid and is found in: • Liver, egg yolk, soybeans, peanuts, legumes, spinach, and wheat germ • Usually lost during food processing

  29. Derived Lipids: STEROLS • Sterols are hydrocarbons with a multiple ring structure • They are hydrophobic and lipophilic • Contain no fatty acids • Cholesterol is the best-known sterol, found only in animal products

  30. CHOLESTEROL: Functions • Major component of cell membranes (especially abundant in nerve and brain tissue) • Precursor molecule: Example - Vitamin D and estrogen are synthesized from cholesterol • Important in the synthesis of bile acids

  31. CHOLESTEROL: Synthesis • The liver manufactures most of the cholesterol in our bodies • The intestine and all cells contribute a small amount • Overall, the body produces about 1000 mg per day • Serum cholesterol levels are homeostatically controlled (set-point)

  32. DIGESTION • Mouth: chewing, lingual lipase, and dietary phospholipids • Stomach: gastric lipase • Small Intestine: CCK = bile, Secretin = pancreatic juice (pancreatic lipase) • Micelles: tiny emulsified fat packets that can enter intestinal cells (enterocytes)

  33. DIGESTIBILITY • Abnormal to find more than 6 or 7% of ingested lipids still intact in the feces • Steatorrhea indicates fat malabsorption • Breast milk • Medium-Chain Trigylcerides • Short-Chain Fatty Acids

  34. ABSORPTION • Most fat absorption takes place in the duodenum or jejunum – micelles carry monoglycerides and free fatty acids to the brush border where they diffuse into enterocytes • Bile salts are absorbed in the ileum (enterohepatic circulation) • Once in the enterocytes, monoglycerides and free fatty acids are reformed into triglycerides • The triglycerides, cholesterol, phospholipids, and protein carriers form LIPOPROTEIN

  35. ABSORPTION • Once these lipoproteins leave the cell, they become CHYLOMICRONS and enter the lymph system • MCTs, short-chain fatty acids and glycerol are absorbed directly into bloodstream. They do not enter the lymph system. • Cholesterol and other sterols are poorly absorbed. Overall, about 50% of dietary cholesterol is absorbed. • Dietary fat increases cholesterol absorption • Fiber (especially soluble fiber) and phytosterols decrease cholesterol absorption

  36. triglycerides

  37. Lipids in the Body • Chylomicrons • Very-Low-Density Lipoprotein • Intermediate-Density Lipoprotein • Low-Density Lipoprotein • High-Density Lipoprotein

  38. Chylomicrons are lipoproteins

  39. Heart Disease • More than 58 million Americans have at least one form of CVD – stroke, hypertension, or coronary heart disease • 1 in 9 women, and 1 in 6 men aged 45-64 years of age have some form of heart disease • Myocardial Infarction (heart attack) is the leading cause of death in American men and women

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