Lipids
Background
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Don’t readily dissolve in water
Three classes: triglycerides, phospholipids, and sterols
Each composed of fatty acids
Fatty Acids
 Composed of long chain of carbons with hydrogen atoms bonded to each carbon
 At one end (alpha end) is an acid (carboxyl group)
 At other end (omega end) is a methyl group
 May be saturated (containing no double bonds) or unsaturated (contain double
bond)
 Saturated fatty acids are linear and melt at higher temps
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palmitic acid, and stearic acid most common
 Unsaturated fatty acids have a kinked shape and melt at lower temps
 MUFAs – one double bond
 Oleic acid most common (found in olive oil)
 PUFAs – two or more double bonds
 Linoleic acid
 Linolenic acid
 Arachidonic acid (ARA)
 Cis and trans (unsaturated) fatty acids
 Cis configuration, liquid at room temp
 Trans configuration, result of partial hydrogenation,
semisolid to solid at room temp, increases shelf life
 FDA test results
 Trans fatty acids raise LDL levels and may lower
HDL levels – causing increased risk to coronary
heart disease – nearly equivalent to saturated fatty
acids
 Therefore, CIS fats are better!
Essential Fatty Acids
 Fatty acids that must be supplied by the diet to maintain health
 Alpha-linolenic acid (omega-3 fatty acid) and linoleic acid (omega-6 fatty acid)
have been identified as essential fatty acids
 They have important roles in immune function and vision, help form cell
membranes, and produce hormone-like compounds called eicosanoids
 The body has no means to produce double bonds between any carbon
atoms from the first to the ninth carbon
 Alpha-linolenic acid and linoleic acid are precursors to eicosanoids
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Alpha-linolenic acid is used to derive
Linoleic acid is used to derive
 Arachidonic acid
 Sources: salmon, sardines, tuna, canola or soybean oil, walnuts,
and flax seeds
Eicosanoids: Used to synthesize
 Prostaglandins (inflammatory response)
 Prostacyclins (inflammatory response)
 Thromboxanes (clotting)
 Lipoxins (inflammation)
Triglycerides
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Composed of glycerol and three fatty acids
Fatty acids are bonded to glycerol by esterification
Deesterification of a triglyceride produces di and monoglycerides
Enzymes in small intestine breakdown triglycerides into free fatty acids and
monoglycerides which are absorbed
Free fatty acids and monoglycerides undergo reesterification and produce triglycerides
that the body needs
Triglycerides in diet and stored in adipose cells provide energy (9 kcal/g)
Principle lipid stored
Insulate the body under skin
Aids in the transportation of fat-soluble vitamins (A, D, E, K)
Phospholipids
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Composed of glycerol, two fatty acids, and phosphorus-containing compound
Example of various phospholipids are lecithins which aid in fat digestion by acting as an
emulsifier
Main component of cell membranes
Sterols
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Multi-ringed structure that doesn’t look like other lipids but yet doesn’t dissolve in water
Cholesterol is a principle example
Cholesterol
 Used to synthesize some hormones
 Precursor to bile acids used in fat digestion
 Essential component to cell membranes
 Made by the body and is consumed in the diet
Fat Digestion and Absorption
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Little or no digestions occurs until fats are in the small intestine
Lecithins and Bile acids (from liver) and enzymes (lipases) from the pancreas digest fats
Monoglycerides and free fatty acids are absorbed through the intestinal membrane
Short and medium chained fatty acids are shuttle into the circulatory system
Long chained fatty acid and monoglycerides are recombined to make triglycerides
In cells of the intestine, triglycerides aggregate and are combined with cholesterol,
protein, and phospholipids to form chylomicrons (lipoprotein particle)
Chylomicrons exit cell via exocytosis, then taken up by lacteals (lymphatic system) in
enterocytes, triglyceride, cholesterol, proteins are combined to form chylomicrons
Fat Transportation
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Chylomicrons are lipoprotein particles surrounded by a thin layer of phospholipids,
cholesterol, and protein
 Thin layer allows for transport in water-based blood
 Once in blood, triglycerides in chylomicron are broken down by the enzyme,
lipoprotein lipase, which is located in blood vessel walls
 Fatty acids and glycerol are released into bloodstream and taken up by body cells
 Remnants of the chylomicron are brought to liver
VLDL – very low density lipoproteins – lipoprotein created in the liver that carries
cholesterol and lipids newly synthesized by the liver
 Once in blood, triglycerides in VLDL are broken down by the enzyme,
lipoprotein lipase, which is located in blood vessel walls
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Because fats are less dense than water, VLDL becomes much heavier and
proportionately denser as triglycerides are released
 The denser VLDL is then termed LDL
 Most LDL is taken up by receptors on liver cells but some LDL can be taken up
by body cells and blood vessel cells
 Blood vessels cell prevent (by oxidizing) LDL to reenter the blood stream –
cholesterol builds up in the cells as well as inner blood vessel walls and over time
forms plaque
HDL – high density lipoproteins – higher proportion of protein – produced by intestine
and liver
 Picks up cholesterol from dead or dying cells and donates the cholesterol to
lipoproteins for transport back to the liver
 It may also block oxidation of LDL
 Therefore HDL slows the development of cardiovascular disease
Fat Replacements/Substitutes
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Water – addition of water, product contains less fat per serving
Carbohydrate based (cellulose, Z-trim, Maltrin, Stellar, and Oatrim) – bind water and
thicken product to give the “feel” of fat
Protein based (Simplesse) – protein globules give food the “feel” of fat
Fat based (Olestra and Salatrim) – linking fatty acids with sucrose
Cardiovascular Disease
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Atherosclerosis
Myocardial Infarction
Cerebrovascular accident
Hypertension
Hyperlipidemia
Familial Hypercholesteremia
Chapter Objectives
After reading chapter six - A student should be able to...
1. List and discuss the three classes of fats in the human body
2. Discuss the difference between an omega end and an alpha end of a fatty acid
3. Describe the structural difference between a mono-unsaturated fatty acid (MUFA) and a
poly-unsaturated fatty acid (PUFA)
4. Discuss the structural and dietary difference between a cis and trans fatty acid
5. Describe why omega-3 and omega-6 fatty acids are considered essential fatty acids
6. Be able to identify various types of essential fatty acids
7. Define what eicosanoids are and their various functions
8. Discuss the structure and reesterification/deesterification of triglycerides
9. Discuss the structure and function of phospholipids and sterols
10. Describe the process of fat digestion and absorption
11. Define: lipases, lecithins, chylomicrons, lacteals, LDL, VLDL, HDL
12. Describe the structure and functions of HDL, LDL, and VLDL
13. Discuss why diets higher in HDL are better than diets high in LDL?
14. List and describe the various types of fat replacement strategies
15. List and discuss various disease related to high dietary fat