Nutri Sci 332: Lipids

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Fatty Acids

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-most common form of lipid in the body
-4-24 carbons, even numbers, 18 C's are most common in foods
-methyl group = omega end
-carboxyl group = alpha end
-not very oxidized so they have a lot of energy and burn well

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Saturated Fatty Acids

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all carbons filled with hydrogens
-C18:0 = 18 C's, no double bonds
-tend to be solid at room temp
-Long chain (>12 C's) solid
-Medium (6-10 C's) can be either
-Short (<6 C's) can be liquids (dairy fats, coconut and palm oils)

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Unsaturated Fatty Acids

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presence of double bonds between carbons (each lacks 2 H's)
-MUFA
-PUFA
-tend to be liquid at room temp

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MUFA

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Monounsaturated Fatty Acid
-single double bond
-canola oil, olive oil, margarine
-high MUFA in diet leads to less heart disease
-mediterranean diet

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PUFA

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Polyunsaturated Fatty Acid
-more than one double bond
-corn, soybean, sunflower, safflower oils

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Fatty Acid Nomenclature

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C=C double bonds are designated as the distance from the methyl group (omega group)
-Oleic acid (C18:1) = omega-9 fatty acid with the first double bond 9 C's away from the methyl end

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4 Most Common Fatty Acids

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1. Stearic Acid (C18:0)
2. Oleic Acid (C18:1)
3. Linoleic Acid (C18:2) => omega-6
4. Alpha-linolenic Acid (C18:3) => omega-3

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Omega Fatty Acids

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Needed for:
-cell membranes
-immune function
-vision
-eicosanoid production and various structural molecules

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Eicosanoids

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made from omega 3 and 6 FA's
-released from cells and act locally, unlike hormones
-20 C polyunsat. FAs
-act as hormone that regulates blood pressure, clotting, immune response, inflammatory response and gastrointestinal secretions

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Triglycerides

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most prominent in our bodies and in nature
-fats (solid) and oils (liquids)
-glycerol + 3 FAs
-provide energy
-energy storage
-insulation and protection
-transport fat-soluble vitamins
-lipases break them down in order to be digested

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Arachidonic acid

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precursor to group 2 series eicosanoids
-inhibited by aspirin and group 3 series

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Group 2 Series Eicosanoids

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-tend to promote vesoconstriction and blood clotting (thromboxane)
-from linoleic acid and arachidonic acid

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Docosahexanoic acid

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DHA
-precursor to Eicosapentanoic acid (EPA) --> group 3 series
-can eat these in fish oil, much more direct way to get omega 3

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Eicosapentanoic acid

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EPA
-precursor to group 3 series
-can eat these in fish oil, much more direct way to get omega 3

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Group 3 Series Eicosanoids

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-tend to promote vessel dilation
-inhibits group 2 series
-synthesized from alpha-linolenic acd

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Linoleic Acid

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-omega-6
-any oil
-used to make group 1 and 2 eicosanoids
-Thromboxan A2 (TXA2)
-1 tblsp of plant oil/day is enough to meet needs

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Thromboxane A2

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TXA2
-made from platelets
-stimulates blood clotting and vasoconstriction
-important during hemorrhage
-may be dangerous in heart disease

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Heart Attack

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-If interior vessel becomes damaged, white blood cells are called in to oxidize lipids which forms a plaque and slows blood flow to an artery

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Alpha-linolenic acid

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-omega-3
-used to make group 3 eicosanoids
-EPA and DHA
-reduce risk of heart disease
-abuse may lead to hemorraghic stroke (bleed to death)
-rich in fatty fish, canola, and soybean oil
-eating those is more effective because it is more direct than alpha-linolenic

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Essential FA Deficiency

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-flaking and itchy skin
-diarrhea
-reduced wound healing
-anemia - low RBC count but high turnover (quick turnovers = more effected).

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Lipase

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enzyme that de-esterifies (hydrolyzes) trigylcerides into free fatty acids, monoglycerides, and glycerol so that they can cross cell membranes

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Phospholipids

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-composted of glycerol and 3 FA's, one containing a phosphorous, and sometimes nitrogen
-emlusifiers (form micelles)
-make up cell membrane
-phospholipid metabolism is important in regulating cell function

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Phosphatidyl choline

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-lecithins
-most common phospholipids
-egg yolk, peanuts

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Micelles

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-phospholipids + triglycerides + water
-essential in lipid digestion and the formation of lipoprotein particles.
-also used in food preparation and cooking

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Cholesterol

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-obtained ONLY from animal sources
-recommend 300mg/day (we consume 200-400)
-corticosteroids (glucocoritcoide)
-sex hormones
-Vitamin D hormone
-bile acids
-cell membranes

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Lipoproteins

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-serve as transport vehicles for TGs in lymph and blood

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Aplipoproteins

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-clusters of lipids associated with proteins
-specific proteins attached to the lipoprotein shell that act to regulate enzymes, facilitate lipid transfer, and direct binding to cell surface receptors

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Chylomicron

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-a lipoprotein that transports diet derived lipids from the small intestine to the lymphatics and then onto the blood
-delivers diet derived lipids to tissues for use and storage

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VLDL

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-created in the liver from dietary and newly synthesized lipids
-carries newly synthesized lipids and cholesterol to tissues
-when it loses TGs --> LDL

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LDL

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-derived from VLDL as cells remove TGs
-composed mainly of cholesterol
-internalized by a receptor pathway mostly in the liver and some other cells
-supplies cholesterol for growth and development of tissues
-alternatively may be scavenged by WBCs which attach to blood vessels and oxidize the lipds forming plaques

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HDL

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-synthesized in the liver and the intestine
-picks up cholesterol from dying cells and transfers it to other lipoproteins and deposits it in the liver for excretion
-ratio of total cholesterol:HDL should be <4:1

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Lipoprotein Lipase

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-enzyme attached to the wall of blood vessels that acts to hydrolyze TGs yielding glycerol and free fatty acids and thereby delivers lipids to surrounding tissues (adipose and muscle)
-recognized by certain apolipoproteins
-activated by insulin
-allows transfer of TG into cell membrane by de-esterification

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Fed State

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-clearance of blood lipids (10-14 hours)
-lipoprotein lipase is insulin sensitive and acts on chylomicrons and VLDL
-lipids are delivered to muscle and adipose

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Fasting State

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-hormone sensitive lipase is activated in adipose tissue by glucagone, norepenephrine
-TG breakdown and mobilization of glycerol and FFAs
-FFAs from adipose are delivered to liver and muscle via albumin

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Glucagone

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made in the pancreas and activates hormone sensitive lipase in adipose tissue
-moves fat out of fat storage

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RI for Cholesterol

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total < 200mg
HDL > 40mg
LDL < 130mg
TG < 200mg

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Hydrogenations of unsaturated FAs

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-FAs with double bonds become oxidized when bonds break and become rancid
-unsaturated vegetable oil --> add H under pressure --> hydrogenated (crisco)
-trans form takes on properties of saturated fat

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Rancidity

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-caused by the oxidation of double bonds caused by oxygen, metals, sunlight
-most likely to occur in foods high in polyunsaturated fats, packaged fried food, fatty foods with large surface areas
-Prevented: BHA, BHT, vitamin E

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Emulsifiers

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-Lecithins
-Monoacylglycerol
-Polysorbate 60

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RI for Fat

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-no RDA for fat
-AI = 20-35% of total energy
-Total fat < 65g
-Saturated fat < 20g
-Cholesterol < 300mg

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Fat Replacements

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-water, starch derivatives and gum
-protein-derived fat replacement (Dairy-Lo)
-Engineered Fats (Olestra)

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Olestra

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derived from carbohydrate of fatty acid chains