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

6. 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

7. 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

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

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

13. 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

16. 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

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

19. Omega 3
Omega 6
Omega 9

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

21. 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

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

23. 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)

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

26. 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

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

28. 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

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

30. Triglyceride
Fatty Acids

31. 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

32. 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

34. 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

35. Protein Channel
Hydrophilic
Hydrophobic

36. 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

37. 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

38. 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

40. 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

41. 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)

42. 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)

43. 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

44. 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

45. 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

47. triglycerides

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

49. Chylomicrons are lipoproteins

50. 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 years of age have some form of heart disease
Myocardial Infarction (heart attack) is the leading cause of death in American men and women

51. Atherosclerosis
A slow, progressive disease that begins in childhood and takes decades to advance.
Basically, plaque (lipid deposits and other substances) forms in response to injuries on the artery wall
Plaque can eventually completely occlude the artery leading to MI
Injury can be caused by: hypercholesterolemia, oxidized LDL, hypertension, smoking, diabetes, homocysteine, and diets high in saturated fat

53. What Are the Lipid Related Risk Factors for CVD?
High LDL Cholesterol and Low HDL Cholesterol
A diet high in cholesterol
A diet high in saturated fat
A diet high in trans-fatty acids

54. Trans Fatty Acids
Trans fatty acids tend to raise total blood cholesterol levels, but less than more saturated fatty acids
Trans fatty acids also tend to raise LDL cholesterol and lower HDL cholesterol
It is not clear if trans fats that occur naturally have the same effect as those produced by hydrogenating vegetable oils
The Food and Drug Administration (FDA) has proposed that the amount of trans fatty acids in a food be included in the Nutrition Facts panel

55. Ingredients: enriched wheat flour, corn syrup, whole oats, raspberry preserves, sugar, partially hydrogenated soybean and/or cottonseed oil, glycerin, maltodextrin, honey, dextrose, natural and artificial flavors, nonfat dry milk, sodium alginate, wheat bran, modified corn starch, salt, cellulose gum, potassium bicarbonate, lecithin, citric acid, xanthan gum, calcium phosphate, malic acid, whey protein concentrate, red #40, blue #1.

56. Other Dietary Considerations
Homocysteine – high levels of this amino acid may promote atherosclerosis, excessive blood clotting, or blood vessel rigidity
Omega-3 Fatty Acids
Soluble Fiber
Antioxidants – clean up free-radicals (Vitamin E, Vitamin C, etc)
Other Phytochemicals – isoflavones and lignans