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Chapter 6: Lipids. Properties of Lipids. Do not readily dissolve in water Fats are solid at room temperature Oils are liquid at room temperature. Functions of Lipids. Provide energy Satiety Flavor and mouth feel Insulation Protect internal organs Transport fat-soluble vitamins
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Properties of Lipids Do not readily dissolve in water Fats are solid at room temperature Oils are liquid at room temperature
Functions of Lipids • Provide energy • Satiety • Flavor and mouth feel • Insulation • Protect internal organs • Transport fat-soluble vitamins • Efficient storage of energy • 80% lipid, 20% protein and water
Triglycerides Triglycerides are the main form of lipids in food and body (storage) Energy dense (9 kcal /g)
Triglycerides Glycerol + 3 FA’s Triglyceride + 3 H20 H H--C--OH H--C--OH H--C--OH H O HO-C-R O HO-C-R O HO-C-R H O H--C--O--C-- O H--C--O--C-- O H--C--O--C-- H R + H2O + R + H20 R + H20
Structure Esterification Joining 3 fatty acids to a glycerol unit De-esterification Release of fatty acids-results in free fatty acids Diglyceride Loss of one fatty acid Monoglyceride Loss of two fatty acids
Structure of Fatty Acids • Fatty acids • Function is dependent on: • Length • Degree of saturation • Location of double bonds • Configuration/Shape • Glycerol backbone
Fatty Acid Chain Length • Long chain FA: > 12 Carbons • Predominant in food (meats, fish) • Medium chain FA: 6 - 10 Carbons • Account for ~4-10% of all FA • Short chain FA: < 6 Carbons • Found in dairy products
Location of Double Bonds • Omega System • Double bond closest to omega (methyl) end • Omega: refers to the last carbon (methyl group) • Omega 6 vs Omega 3 fatty acids • Delta (alpha) System • Uses the carboxyl end and indicates location for all double bonds
Fatty Acid Structure omega end alpha end H H H H H H H H H H H H H H H H H O H-C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C-C-OH H H H H H H H H H H H H H H H H H
Configuration/Shape cis versus trans
Saturated Fatty Acids • Fatty acids with no double bonds • Solid at room temperature • Animal fats: • Dairy: cheeses, ice cream, whole milk • Meat: beef, pork, lamb, • Plant/tropical oils (cottonseed, coconut) • Stearic, lauric, myristic, palmitic
Trans Fatty Acids risk for heart disease • Essentially a saturated fat • Raise LDL • Lower HDL • Intake has increased dramatically • Found in margarine, cookies, potato chips, snack chips, onion rings • Current intake is~3% of total kcals
Hydrogenation of Fatty Acids Process used to solidify an oil Addition of hydrogen to an unsaturated fatty acid (eliminating the double bond—making it into a saturated fatty acid) Trans fatty acids are a by product of hydrogenation How can we limit intake of these?
Food Labels • % Daily Value on Nutrition Facts label is sum of trans and saturated fatty acids • Quantity of trans fatty acids • “Trans fat free” has no more than 0.5 g each of trans or saturated fat • Read the food label and look for hydrogenated or partially hydrogenated oils, or trans fatty acids
Monounsaturated Fatty Acids One double bond Oleic acid (Omega 9) Olive oil, canola oil, nuts Rate of CHD low in Mediterranean countries where diet is rich in olive oil Diet high in MUFA equivalent to low-fat diet in ↓ LDL-C, but does not ↓ HDL-C
Polyunsaturated Fatty Acids • 2 or more double bonds • Provides essential fatty acids (EFAs) • Omega 3 • Omega 6 • Properties differ between these EFAs
Essential Fatty Acids • Polyunsaturated fatty acids • Body can only make double bonds after the 9th carbon from the omega end • Needed for • immune function • vision • cell membranes • production of hormone-like compounds
Essential Fatty Acid Needs Adequate Intake Approximately 2-4 Tablespoons daily Deficiency Unlikely Toxicity No upper level set 32
Omega-3 Fatty Acids Linolenic acid (α-linolenic acid) Forms eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) Metabolized to form eicosanoids
Omega-3 Fatty Acids • Consumption of large amounts of omega-3 fatty acids decreases the ability of blood to clot • May: • Prevent stroke and heart attacks caused by clots (thrombosis) • Reduce risk of stroke caused by blood clots • Help some chronic inflammatory conditions • Asthma, rheumatoid arthritis, psoriasis
Omega-3 Fatty Acids • Recommend intake of ~2 servings of fish/wk • Shellfish • Cold water/fatty fish (salmon, mackerel, sardines, tuna) • Consumption of canola or olive oil vs. other plant oils • Flaxseed oil • 2 tbsp per day • Fish oil capsules • 900 mg per day • Avoid: if have a history of bleeding disorder, on blood thinners
Omega-6 Fatty Acids • Linoleic acid • Forms arachidonic acid • Metabolized to eicosanoids • Found in vegetable oils • Corn, sunflower, safflower, soybean oils, nuts, seeds, wheat germ • Only need ~ 1 tablespoon a day
Eicosanoids • A group of hormone-like compounds • By-pass the blood stream and work in the area of origin • Regulators of: • Blood pressure • Clotting • Immune responses • Inflammatory responses • Stomach secretions • Prostaglandins, thromboxanes, leukotrienes, prostacyclins, lipoxins
Eicosanoids Have Different Effects • Omega-3 eicosanoids, DHA, EPA • ↓ blood clotting • ↓ inflammatory responses • Reduce heart attack • Excess may cause hemorrhagic stroke • Omega-6 eicosanoids; Arachidonic acid • ↑blood clotting • ↑ inflammatory responses • Eicosanoids have different effects on different tissues
American Heart Association Recommendations Total fat: <30% of total calories Saturated fat: <10% of total calories Monounsaturated fat: 10% of total calories Polyunsaturated fat: 10% of total calories Cholesterol: <300 mg/day
Phospholipids Hydrophobic and Hydrophillic Ends Functions Component of cell membranes Eicosanoid synthesis Emulsifier Allows fats/lipids to be dispersed in water Bile acids Sources Synthesized by the body as needed Built on a glycerol backbone At least one fatty acid replaced with phosphorus compound Food: egg yolks (lecithin), wheat germ and peanuts
Emulsifier Hydrophilic end (attracts water) Hydrophobic end (attracts lipid)
Sterols Multi-ringed structure, most known is cholesterol Functions Bile acids, cell membranes Precursor of steroid hormones, sex hormones, adrenal hormones, Vitamin D Sources Synthesized by the liver Food: animal origin
Lipid Digestion • Mouth • Lingual lipase (inactive until reaches stomach) • Stomach • Gastric lipase (digests primarily SCFAs) • Muscular contractions mix fat with digestive enzymes • Fats generally remain in stomach 2-4 hours
Lipid Digestion • Small intestine • Cholecystokinin (CCK) and Secretin • Released due to presence of fat in duodenum • CCK stimulates release of • Pancreatic lipase • Bile (to help emulsify fat) • Secretin stimulates release of • Bicarbonate • Raises pH for activation of lipases
Bile • Composed of bile acids, bile pigments, phospholipids (lecithin) • Synthesized from cholesterol in the liver • Function is to emulsify fat • Allows fat to be suspended in watery digestive juices • Large fat globules broken down to smaller ones, surface area for lipase action increases • Micelles are formed