Lipids

1. Lipids Readings: Chapter 5

2. What are Lipids? organic compounds that dissolve readily in organic solvents but poorly in aqueous solutions “hydrophobic” = water fearing “lipophilic” = fat loving three main classes of lipids: triglycerides phospholipids sterols

3. Fatty Acids: Building Blocks of Lipids fatty acids are molecules composed of a chain of carbon and hydrogen molecules with a methyl group at one end and an acid group at the other end ACID group “alpha end” METHYL group “omega” end

4. Classification of Fatty Acids Fatty acids are classified based on: - LENGTH of the carbon chain - degree of SATURATION - location of DOUBLE BONDS - ISOMERIC forms

5. Classification of Fatty Acids a) Length the # of carbon molecules in the chain can be 4 - 24 carbons long most common in food are 18 carbon fatty acids short chain fatty acids are more liquid and are more soluble in water

6. Classification of Fatty Acids cont. b) Degree of Saturation refers to the # of hydrogen atoms (H+) bound to the carbon atoms “double bonds” reduce the # of H+ making a fatty acid LESS SATURATED refer to as: SATURATED MONOUNSATURATED POLYUNSATURATED foods contain a mixture of fatty acids

7. Saturated Fatty Acids no double bonds between carbon atoms solid at room temperature example: stearic acid common sources: animal fats (butter, lard, beef tallow, etc…), cocoa butter, palm oil, coconut oil

8. Monounsaturated Fatty Acids (MUFA) have a single double bond liquid at room temperature examples: oleic acid common sources: olive oil, canola oil, peanut oil

9. Polyunsaturated Fatty Acids (PUFA) two or more double bonds liquid at room temperature examples: a-linolenic acid & linoleic acid essential nutrients common sources: flax seed oil, safflower oil, soy bean oil, cottonseed oil, fish

10. c) Location of Double Bonds measured from the methyl end (also called the omega end, abbreviated “w”) to the first double bond Classification of Fatty Acids cont. double bond H H H H H H H H H H H H H H H H H O = 1 2 H–C–C–C=C–C–C=C–C–C=C–C–C–C–C–C–C–C–C–O–H 3 H H H H H H H H H H H = omega 3 fatty acid methyl end

11. Classification of Fatty Acids cont. c) Location of Double Bonds cont.

12. Classification of Fatty Acids cont. d) Isomeric Forms molecules that have the same atoms but have different geometric or positional arrangements

13. Non-Essential & Essential Fatty Acids the body is able to synthesize most fatty acids as needed desaturation: e.g. removes H+ from stearic acid to make oleic acid elongation: e.g. adds carbons to build storage and structural fats the body cannot make fatty acids that have double bonds before the 9th carbon omega 3 & omega 6 must be provided in the diet = ESSENTIAL FATTY ACIDS

14. Essential Fatty Acids Omega 3 Fatty Acids polyunsaturated fatty acids with 1st double bond three carbons from the methyl end Examples: linolenic acid, EPA, DHA Sources: canola, soybean, flaxseed oil, walnut oils, fatty fish (tuna, salmon, sardines, etc..)

15. Omega 3 Fatty Acids in Selected Foods Table 5.3, page 176

16. Omega 6 Fatty Acids polyunsaturated fatty acids with 1st double bond six carbons from the methyl end Examples: linoleic acid, arachidonic acid Sources: sunflower, corn, peanut, cottonseed, soybean oils Essential Fatty Acids

17. Functions of the Essential Fatty Acids most fatty acids used to provide energy small proportion used to make eicosanoids Examples: thromboxanes prostaglandins leukotrienes

18. Functions of Eicosanoids If derived from w-3 fatty acids… vasodilation inhibition of blood clotting reduce inflammation lower blood cholesterol If derived from w-6 fatty acids… vasoconstriction promote blood clotting promote inflammation

19. Classes of Lipids: Triglycerides most abundant form of lipid both in our DIET and in our BODY formed from 3 FATTY ACIDS attached to a GLYCEROL backbone Fatty Acids Glycerol

20. Formation of Triglycerides occurs via a condensation reaction, produces ester bonds

21. Triglyceride Composition most triglycerides contain a mixture of more than one type of fatty acids, such that they may contain saturated, MUFA, and PUFA

22. Functions of Triglycerides a) energy source in normal conditions supplies 60% of energy needs during rest preferred fuel of heart, resting muscles b) Satiety value - provides satisfaction from meal c) energy reserve stored in adipocytes to provide energy during times of energy deficit 1 g of fat stores provides > 6x as much energy as 1 g of glycogen!

23. d) insulation & protection visceral fat cushions & shields organs subcutaneous fat protects & insulates the body e) transport of fat soluble vitamins Vitamins A, D, E, K, carotenoids, other phytochemicals f) sensory qualities contributes to the flavour, texture, & odour of food Functions of Triglycerides cont.

24. Classes of Lipids: Phospholipids formed from a backbone of glycerol with 2 fatty acids, a phosphate, and a nitrogen containing group (e.g. choline) synthesized in body by the liver soluble in both water and lipids

25. a) form cell membranes b) lipid transport form surface of lipid transport molecules called lipoproteins, allowing lipids to dissolve in the blood Functions of Phospholipids

26. Functions of Phospholipids cont. c) emulsifiers facilitate mixing of lipids and water due to ability to dissolve in both water and oil

27. NOT essential nutrients! Examples: phosphatidyl choline, lecithins common food sources: eggs liver soybeans wheat germ peanuts Phospholipids in the Diet

28. Classes of Lipids: Sterols carbon atoms form RINGS do not contain fatty acids both lipophilic and hydrophobic not essential nutrients example: cholesterol found only in animal foods

29. Functions of Sterols a) Component of cell membranes provide structure abundant in brain and nervous tissues b) Precursor to other substances steroid hormones (e.g. cortisol, testosterone, aldosterone, estrogen) Vitamin D bile acids

30. Lipid Digestion & Absorption Mouth & Stomach lingual lipase secreted in saliva, gastric lipase secreted by stomach- small contribution to digestion mechanical digestion of chewing and gastric mixing keep fat dispersed after 2 - 4 hours in the stomach, about 30% of lipids broken down to diglycerides and free fatty acids

31. Lipid Digestion & Absorption Small intestine presence of fat in the small intestine stimulates secretion of: - CCK - secretin - GIP bile contains bile salts & phospholipids which emulsify fats

33. Lipid Digestion & Absorption pancreatic lipase cleaves 1 fatty acid off triglycerides at a time, produces free fatty acids & monoglycerides sterols remain unchanged by digestion or are esterified bile salts surround the products of lipid digestion forming micelles and transport digested lipid to intestinal cell surface bile salts are recycled monoglycerides & fatty acids are absorbed by passive diffusion

34. Lipid Digestion & Absorption monoglycerides & long chain fatty acids reform triglycerides triglycerides, cholesterol, and phospholipids combine with proteins to form chylomicrons, a type of lipoprotein glycerol, short & medium chain fatty acids are absorbed directly into the blood

35. Lipids in the Body: Transport some short chain fatty acids (& glycerol) travel freely in blood most lipids require transporters called lipoproteins

36. Classes of Lipoproteins Chylomicrons transport diet derived lipids from small intestine to body tissues contain mostly triglyceride (~ 90%) and very little protein, lowest density the enzyme lipoprotein lipase splits off triglycerides from the chylomicron fatty acids may also be taken up by muscle cells

37. Classes of Lipoproteins Very Low Density Lipoproteins (VLDL) synthesized by liver & intestines lipoprotein lipase splits off and hydrolyzes triglycerides from VLDL as it circulates as it loses triglycerides becomes an intermediate density lipoprotein (IDL) IDL are about 40% triglycerides pick up cholesterol from HDL return to the liver & converted to LDL

38. Classes of Lipoproteins Low Density Lipoproteins (LDL) contain more than 50% cholesterol deliver cholesterol to the body cells LDL binds to a receptor on the surface of cell membranes, triggering the cell to engulf the LDL molecule contain a protein called Apo B facilitates cell uptake of cholesterol and triglycerides

39. Classes of Lipoproteins Low Density Lipoproteins (LDL) cont. other LDL receptors found on liver cells regulate blood levels of cholesterol receptors are blocked by saturated and trans fatty acids immune cells called macrophages also have scavenger receptors for LDL uptake of LDL by macrophages implicated in development of atherosclerosis

40. Classes of Lipoproteins High Density Lipoproteins (HDL) made in the liver & intestines contains highest proportion of protein of all lipoproteins scavenges cholesterol and transfers the cholesterol to other lipoproteins (IDL) for return to the liver contains a protein called Apo E which activates receptors in the liver for uptake

41. Figure 5-25, page 190

42. Blood Lipids & CVD elevated blood lipids are a risk factor for cardiovascular disease (CVD) assess risk by examining blood levels of: triglycerides total cholesterol LDL HDL

43. Blood Lipids & CVD Elevated Triglycerides linked to excess body fat, physical inactivity, cigarette smoking, Type II Diabetes, others most often seen in individuals with other lipid abnormalities optimal levels below 150 mg / dL blood

44. Blood Lipids & CVD Elevated Total Cholesterol also linked to excess body fat, physical inactivity, cigarette smoking, Type II Diabetes, others optimal levels below 200 mg / dL blood

45. Blood Lipids & CVD LDL = “BAD” Cholesterol transport lipids from liver to the tissues elevated levels a risk factor for cardiovascular disease excess LDL in blood is susceptible to:

46. Blood Lipids & CVD LDL = “BAD” Cholesterol cont. oxidized LDL (oxLDL) causes damage to blood vessel walls, initiating the development of atherosclerosis oxLDL taken up by macrophages through scavenger receptors macrophages become filled with lipids and are called foam cells results in build up of a fatty plaque on the blood vessel wall

48. Blood Lipids & CVD LDL = “BAD” Cholesterol cont. LDL particles may vary in size and density small dense LDL   risk of CVD risk is also dependant on the specific proteins found within the LDL particle example:  risk for apo B and apo A-1 optimal levels less than 100 mg / dL Think “L” = “less healthy” or “lethal”

49. Blood Lipids & CVD HDL = “GOOD Cholesterol” transports lipids from tissues to the liver high levels  risk of CVD low levels  risk of CVD ratio of HDL:LDL (or HDL:total cholesterol) also important ( 1:2 = low risk) regular physical activity helps  HDL optimal levels greater than 60 mg / dl Think “H” = “healthy”

50. Note: you cannot eat either LDL or HDL!