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Chapter 5: Fats, Oils and Other Lipids Presentation created by Jill Goode Englett, University of Alabama and Ellen Brennan, San Antonio College Lipids Organic compounds which do not dissolve in water but do dissolve in fat solvents Classes of lipids • Triglycerides • Sterols • Phospholipids © 2010 Pearson Education, Inc. Lipids Basic functions in the body • Fats - Store and provide energy (9 kcal per gram) - Provide insulation - Provide structure • Cholesterol - Cell membrane structure - Used to make steroid hormones, bile, and provitamin D • Phospholipids - Help transport fat-soluble nutrients in the blood - Cell membrane structure © 2010 Pearson Education, Inc. Fatty Acids Building blocks for triglycerides and phospholipids A chain of carbon and hydrogen atoms with a carboxyl group at the alpha end and a methyl group at the omega end © 2010 Pearson Education, Inc. Figure 5.1 Fatty Acids Higher ratio of carbon and hydrogen to oxygen than in carbohydrates and protein 20 different fatty acids with varied length, saturation, and shape Different structures impart different characteristics © 2010 Pearson Education, Inc. Fatty Acids Vary in Length Short-chain fatty acids • Two to four carbons • Liquid at room temperature Medium-chain fatty acids • Six to ten carbons Long-chain fatty acids • 12 or more carbons • Most common type of fatty acid in foods © 2010 Pearson Education, Inc. Fatty Acids Vary in Degree of Saturation Saturated fatty acids • All the carbons on the fatty acid are bound to hydrogen • Usually more solid at room temperature • Higher melting point • More stable © 2010 Pearson Education, Inc. Fatty Acids Vary in Saturation Unsaturated fatty acids • Some carbons form a double bond with each other instead of binding to hydrogen • Monounsaturated fatty acid (MUFA) - Has one carbon to carbon (C=C) double bond • Polyunsaturated fatty acid (PUFA) - Has two or more carbon to carbon (C=C)double bonds • More liquid at room temperature • Lower melting point • Less stable © 2010 Pearson Education, Inc. Saturated and Monounsaturated Fatty Acids © 2010 Pearson Education, Inc. Saturated and Unsaturated Fatty Acids Help Shape Foods Figure 5.3 Fatty Acids Differ in Double-Bond Location The location of the first double bond in unsaturated fatty acids affects the naming and characteristics of the unsaturated fatty acids Omega-3 fatty acid • First double bond is between the third and fourth carbon from the omega end • Example: alpha-linolenic acid (ALA) - One of the two essential fatty acids © 2010 Pearson Education, Inc. The Essential Fatty Acids: Omega-3 and Omega-6 Figure 5.4 Fatty Acids Differ in Double-Bond Location Omega-6 fatty acid • First double bond is between the sixth and seventh carbon from the omega end • Example: linoleic acid - One of the two essential fatty acids © 2010 Pearson Education, Inc. Unsaturated Fatty Acids Vary in Shape Unsaturated fatty acids form two different shapes © 2010 Pearson Education, Inc. Figure 5.5 Fatty Acids and Rancidity Rancidity: spoiling of fats through oxidation • The more double bonds there are, the more susceptible to oxidation and rancidity PUFA > MUFA > Saturated fatty acids Ways to enhance stability of fatty acids and reduce rancidity • Adding antioxidants • Limiting food exposure to oxygen, heat, and light • Hydrogenation (partial or full) © 2010 Pearson Education, Inc. Hydrogenation Adding Hydrogen to an unsaturated fatty acid Hydrogenation: Benefits and Risks Benefits of hydrogenation • Makes food fats more stable, increasing shelf life • Changes the texture of the fat - Oils become more spreadable - Changes the characteristics of baked goods Risks of hydrogenation • Increases amount of trans fatty acids in foods with partially hydrogenated oils - Increases liver production of LDLs - Decreases liver production of HDLs © 2010 Pearson Education, Inc. Trans Fatty Acids Formed During Partial Hydrogenation © 2010 Pearson Education, Inc. Quick Review Fatty acids • Carbon and hydrogen chain, carboxylic acid, methyl group • Basic structural units of triglycerides and phospholipids • Differ in chain length, degree of saturation, shape - Saturated fatty acids: no carbon to carbon double bonds - Monounsaturated fatty acids: one C=C double bond - Polyunsaturated fatty acids: two or more C=C double bonds • Essential fatty acids - Linoleic - Alpha-linolenic acid • Food manufactures hydrogenate or add antioxidants to unsaturated fatty acids to reduce susceptibility to rancidity © 2010 Pearson Education, Inc. Triglycerides Three fatty acids connected to a glycerol backbone © 2010 Pearson Education, Inc. Portion of Figure 5.7 Triglycerides Most common lipid both in foods and in the body Make up about 95% of lipids found in foods Functions • Add texture • Add flavor to foods • Make meats tender • Energy storage in adipose tissue © 2010 Pearson Education, Inc. Caution: High levels in the blood are a risk factor for heart disease Phospholipids Hydrophilic on one end; hydrophobic on the other Make up the phospholipid bilayer in the cell membrane • Lecithin (a.k.a. phosphatidylcholine) - A major phospholipid in the cell membrane - Used as an emulsifier in foods Synthesized by the liver © 2010 Pearson Education, Inc. Portion of Figure 5.8 Phospholipids’ Role in Cell Membranes Figure 5.9 Sterols More complex than phospholipids or triglycerides • Four connecting rings of carbon and hydrogen Do not provide energy Cholesterol is the best known sterol; Not essential in diet • Part of cell membrane structure • Used to make bile, steroid hormones, provitamin D Phytosterols – major plant sterols © 2010 Pearson Education, Inc. Figure 5.11 Quick Review © 2010 Pearson Education, Inc. Figure 5.12 Fats in Food | Fats in Food Quick Review Triglycerides • Found in the body • Stored in the adipose tissue • Major source of energy Phospholipids • An important part of cell membrane structure • Lecithin - Part of cell membrane - Used as an emulsifier in some foods Sterols • Do not contain fatty acids • Do not provide energy © 2010 Pearson Education, Inc. What Happens to the Lipids You Eat? Lipids from foods • Fat, phospholipids, and sterols Emulsified by bile Fats are digested by lipase into • Free fatty acids, glycerol, and monoglycerides © 2010 Pearson Education, Inc. Figure 5.13 Figure 5.13 Figure 5.13 Figure 5.13 Most Fat Is Digested and Absorbed in the Small Intestine Fat tends to cluster in the chyme Fat stimulates the secretion of cholecystokinin (CCK) from the duodenum CCK stimulates the gallbladder to release bile and the pancreas to release pancreatic lipase Bile emulsifies fat, increasing the surface area of the fat droplets The triglycerides in the smaller fat droplets can then be digested by pancreatic lipase © 2010 Pearson Education, Inc. Handling of Sterols and Phospholipids in the Small Intestine Sterols • Not digested • Absorbed intact through intestinal membrane • Those which bind with fiber are not absorbed in small intestine and are excreted in the feces Phospholipids • Digested by phospholipases © 2010 Pearson Education, Inc. Lipid Absorption Short- and medium-chain fatty acids can be absorbed directly into the portal circulation Glycerol and long-chain fatty acids are absorbed from micelles in the intestinal lumen into the intestinal lining cells Once in the intestinal lining cells - Triglycerides are reformed - The triglycerides combine with phospholipids, cholesterol and protein to form chylomicrons © 2010 Pearson Education, Inc. Chylomicrons Facilitate Lipid Absorption Chylomicrons are too large to be absorbed directly into the bloodstream • Absorbed via the lacteal and into the lymph • Lymph later enters blood stream through thoracic duct near the heart © 2010 Pearson Education, Inc. Figure 5.15 Absorption of Dietary Lipids Figure 5.16 Serum Lipoproteins Transport Lipids Through the Blood Serum lipoproteins are composed of differing amounts of fat (TG), cholesterol, phospholipid (PL), and protein • Chylomicrons – mostly dietary fat • Very low-density lipoproteins (VLDLs) – mostly fat made by the liver • Low-density lipoproteins (LDLs) – mostly cholesterol • High-density lipoproteins (HDLs) – mostly protein © 2010 Pearson Education, Inc. The Ratio of Protein to Lipid Determines the Density of the Lipoprotein Figure 5.17 Serum Lipoproteins Transport Lipids Through the Blood Very low-density lipoproteins (VLDLs) are made in the liver and they are mostly triglyceride As the VLDLs deliver triglycerides to the adipose tissue and other cells, they shrink in size and become LDLs LDLs are mostly cholesterol and are sometimes called “bad” cholesterol because they can contribute to plaque formation in arteries. Liver should remove these from the blood. HDLs are made by the liver and are sometimes “good” cholesterol because they can remove deposited cholesterol from plaque © 2010 Pearson Education, Inc. The Roles of VLDL, LDL, and HDL Lipoproteins Figure 5.18 Lipoproteins | Lipoproteins Quick Review Most fats are digested in the small intestine with the help of bile acids and pancreatic lipase Short- and medium-chain fatty acids are absorbed directly into the bloodstream Longer chain fatty acids and other remnants of fat digestion • Packaged in chylomicron lipoprotein carriers • Travel in lymph before entering the bloodstream Lipoproteins are globular shaped transport carriers • Outer shell high in protein and phospholipids • Inner core carries insoluble fat, cholesterol, and other lipids through lymph and bloodstream © 2010 Pearson Education, Inc. Quick Review VLDLs and HDLs are synthesized in the liver VLDLs eventually become LDLs after depositing some fatty acids in the body’s cells LDLs deposit cholesterol in the cells and arterial walls HDLs remove cholesterol from the arteries and deliver it to the liver to be used in the synthesis of bile or excreted in the feces © 2010 Pearson Education, Inc. Functions of Fat Source of energy Preferred storage form of energy in animal body Form body structures Regulate metabolism (eicosanoids) Enhance absorption of fat-soluble vitamins Provide insulation to help regulate body temperature Cushion major organs © 2010 Pearson Education, Inc. Fat Is Used as Energy Fat • Provides concentrated source of kilocalories - 9 kilocalories per gram • Readily available when the body needs energy • Body’s main source of energy throughout the day • Stored in adipose tissue (subcutaneous, intra-abdominal, layered through muscles) © 2010 Pearson Education, Inc. Fat Is Used as Energy Fat • Fat can be synthesized (lipogenesis) in both the liver and the adipose tissue from any source of kcals • Body has an unlimited ability to store excess energy as fat in adipocytes - Fat synthesized in the liver is carried to the adipose tissue for storage on VLDLs - Fat cells have the capacity to enlarge as much as 1,000 times their original size - Body has the ability to produce additional fat cells © 2010 Pearson Education, Inc. Fat Is Used as Energy Preferred source of energy for the heart, liver, and muscles Fat cannot sustain life alone • Some glucose is also needed • Only the glycerol from the fat can be converted to glucose © 2010 Pearson Education, Inc. Fat Helps Insulate and Protect Fat in subcutaneous tissue • Insulates body • Maintains body temperature Fat protects bones and vital organs from trauma • Too much fat eliminates the protective benefit • Too little puts the body at risk © 2010 Pearson Education, Inc. Role of Adipose Tissue in Fat Metabolism Fat synthesis (lipogenesis) • Stimulated by insulin after a meal Fat storage • LPL (lipoprotein lipase) breaks down TG from Chylomicrons and VLDLs to move the glycerol and fatty acids into the cells where TGs are resynthesized Fat breakdown (lipolysis) • HSL (hormone sensitive lipase) breaks down stored TG into fatty acids and glycerol to return to the blood as energy is needed • HSL is activated by glucagon, cortisol, thyroxine, ACTH, growth hormone, epinephrine and norepinephrine © 2010 Pearson Education, Inc. Role of Lipoprotein Lipase © 2010 Pearson Education, Inc. Other Roles of the Adipose Tissue Immune function Inflammation Endocrine • Activates some hormones • Makes adipokines: Peptide hormones produced by the fat cells - Leptin: signals brain to decrease food intake and increase BMR. Levels increase with obesity, but brain becomes resistant to the signal. - Adiponectin: in normal amounts this hormone has antiinflammatory and possibly anti-diabetic functions. Levels decrease with obesity, and high levels can cause some autoimmune diseases © 2010 Pearson Education, Inc. Fat Cells (Adipoctyes): © 2010 Pearson Education, Inc. Essential Fatty Acids: Cell Membrane Structure Linoleic acid • Essential fatty acid of the omega-6 family • Can be elongated and converted to arachidonic acid (20C) Alpha-linolenic acid Essential fatty acid of the omega-3 family Can be elongated and converted to - eicosapentaenoic acid (EPA), 20C - EPA can be elongated to docosahexaenoic acid (DHA), 22C • Needed for healthy cell membranes • Especially concentrated in brain, eye, and other nervous tissue © 2010 Pearson Education, Inc. Essential Fatty Acids: Eicosanoids EPA and arachidonic acid are used to manufacture eicosanoids Eicosanoids are hormone-like substances • Prostaglandins, thromboxanes, and leukotrienes • Help regulate the immune system, blood clotting, inflammation, smooth muscle contraction, and blood pressure © 2010 Pearson Education, Inc. Quick Review Fat • An energy-dense source of fuel • Cushions and protects bones, organs, and nerves • Helps maintain body temperature • Provides essential fatty acids • Is needed for the absorption of fat-soluble vitamins and carotenoids Essential fatty acids are precursors to Arachidonic acid, EPA and DHA which manufacture • Regulate the immune system • Prostaglandins • Regulate blood clotting • Thromboxanes • Regulate inflammation • Leukotrienes • Regulate blood pressure © 2010 Pearson Education, Inc. Quick Review Essential functions of cholesterol • Is part of cell membrane • Is needed to make - Provitamin D - Bile acid - Steroid hormones © 2010 Pearson Education, Inc. How Much Fat Do We Need Each Day? Acceptable Macronutrient Distribution (AMDR) Range • 20–35% of daily kilocalories from fat For heart health • Consume no more than 10% of total kilocalories from saturated fat • Limit trans fats to < 1% of total kcals © 2010 Pearson Education, Inc. © 2010 Pearson Education, Inc. Best Food Sources of Fat Sources of unsaturated fats © 2010 Pearson Education, Inc. Figure 5.20 Food Sources of DHA and EPA Figure 5.21 Facts About Fats, Oils, and Cholesterol High intake of trans fats and saturated fats increases risk of • Cardiovascular disease • Stroke • Cancer Substituting or replacing trans fats and saturated fats with MUFA and PUFA can lower risk © 2010 Pearson Education, Inc. Foods Containing Trans Fat Hydrogenated fats are used by many commercial food producers to • Provide rich texture • Increase shelf live • Decrease rancidity Some trans fats are naturally occurring During the partial hydrogenation process additional trans fats form © 2010 Pearson Education, Inc. Trans Fatty Acids Formed During Partial Hydrogenation © 2010 Pearson Education, Inc. Major Food Sources of Trans Fat for American Adults Figure 5.23 Trans Fats Trans fat may actually be worse for heart health than saturated fats • Raise LDL cholesterol • Lower HDL cholesterol FDA requires trans fat to be listed on food labels in the Nutrition Facts panel Must also look at the ingredient label for partially hydrogenated fatty acids to identify if there are any trans fatty acids in a processed food The food industry is working to find replacements for trans fats in foods © 2010 Pearson Education, Inc. Where’s the Saturated Fat in Foods? Figure 5.22 Dietary Cholesterol Is Not Essential The liver synthesizes cholesterol needed by the body • Liver synthesizes ~900 mg/d • Liver decreases synthesis based on dietary intake to some extent • Any extra source of calories can be converted to cholesterol by the liver, greatest effect from - saturated fatty acids - trans fatty acids To reduce the risk of cardiovascular disease, dietary cholesterol intake should be limited to < 300 mg/day © 2010 Pearson Education, Inc. Food Sources of Cholesterol and Plant Sterols Cholesterol comes from animal foods only Phytosterols and stanols are plant sterols • Lower LDL levels by competing with cholesterol for absorption • Are found in soybean oil, many fruits, vegetables, legumes, sesame seeds, nuts, cereals, and other plant foods • Some food manufacturers are fortifying foods with them to help lower cholesterol © 2010 Pearson Education, Inc. Which MyPlate Food Groups Contain Fat? © 2010 Pearson Education, Inc. Quick Review Dietary lipids are an important part of a healthy diet, especially essential fatty acids Saturated fat, trans fats, and cholesterol intake should be limited Dietary fat intake per day • Should range from 20 to 35% of total kilocalories • 5–10% of kilocalories from linoleic acid • 0.6–1.2% of kilocalories from alpha linolenic acid • Limit saturated fat intake to < 10% of total fat intake • Limit trans fat intake to < 1% of total fat intake • Limit cholesterol intake to < 300 mg © 2010 Pearson Education, Inc. Quick Review Lean meat and poultry, fish, low-fat or nonfat dairy products and limited amounts of nuts and cheese • Best sources of essential fatty acids • Limit intake of saturated and trans fats Commercially prepared baked goods and snack items • Are high in kilocalories • Are high in saturated and trans fats • Should be consumed rarely Use vegetable oils in the place of butter © 2010 Pearson Education, Inc. Quick Review Trans fats are made by heating oil and adding hydrogen gas to saturate some of the carbons of the fatty acids Trans fats raise LDL cholesterol and lower HDL cholesterol Trans fats are found in many commercially prepared foods and must be listed on the food label Other oils are being tested to replace trans fats in foods Cholesterol is found in animal foods Phytosterols are found in vegetable oils, nuts, legumes, whole grains, fruits, and vegetables © 2010 Pearson Education, Inc. Fat Substitutes Designed to provide the creamy properties of fat for fewer kilocalories Fall into three categories • Carbohydrate-based: Majority of fat substitutes • Protein-based: Provide a creamy texture in the mouth • Fat-based: Give physical attributes of fat for fewer kilocalories Overconsumption of kilocalories from regular, low-fat, or fat-free products can lead to weight gain © 2010 Pearson Education, Inc. Quick Review Fat substitutes provide the properties of fat for fewer kilocalories and grams of fat Fat substitutes can be carbohydrate based, protein based, or fat based Some substitutes such as olestra work by passing unabsorbed through the GI tract Reduced-fat and fat-free foods still contain kilocalories and should be eaten in limited amounts © 2010 Pearson Education, Inc. What Is Heart Disease and What Factors Increase Risk? Cardiovascular disease is the number-one killer of adults in the United States Fat and Cholesterol Accumulate in the arteries © 2010 Pearson Education, Inc. Arteries narrow Blood flow is impeded Decrease oxygen and nutrients • Not enough oxygen to the heart • CHEST PAIN Atherosclerosis Figure 5.24 Emerging risk factors • C-reactive protein (CRP) • Homocysteine • Chlamydia pneumoniae • Lp(a) protein • Metabolic Syndrome Quick Review Heart disease is the leading cause of death in the United States It develops when atherosclerosis causes narrowing of the coronary arteries and decreased flow of oxygen and nutrients to the heart Elevated LDLs are a major risk factor Uncontrollable risk factors include age, gender, family history, and type 1 diabetes Controllable risk factors include type 2 diabetes, high blood pressure, smoking, physical inactivity, excess weight, low HDLs, elevated LDLs HDLs can be raised by losing weight, regular exercise, and quitting smoking Metabolic Syndrome is a group of risk factors © 2010 Pearson Education, Inc. Recommended Serum Lipid Levels Total serum cholesterol should not exceed 200mg/dl HDL cholesterol should be 40 mg/dl or greater in men HDL cholesterol should be 55 mg/dl or greater in women LDL cholesterol should be below 100 mg/dl Serum triglycerides should be below 150 mg/dl © 2010 Pearson Education, Inc. Lowering LDLs and Increasing HDLs Consume less saturated and trans fats Avoid excessive Calorie intake Consume less cholesterol Make smart, informed food choices • Avoid or consume processed food in moderation • Eat at least two servings of fish per week • Consume more plant © 2010 Pearson Education, Inc. foods • Consume antioxidants and phytochemicals • Garlic may help lower cholesterol • Flavonoids may help prevent LDLs from oxidizing Exercise Alcohol, in moderate amounts, can reduce the risk of heart disease Healthy Fats in Foods http://www.hsph.harvard.edu/nutritionsource/questions /omega-3/index.html © 2010 Pearson Education, Inc. Lipid Information on Label © 2010 Pearson Education, Inc. Putting It All Together For optimal long-term health a diet should include a proper balance of all nutrients including fat There are different types of lipids, some essential and others not required from foods Goal • Consume mostly unsaturated fats • Limit amount of saturated and trans fats A plant-based diet plentiful in whole grains, fruits, and vegetables, with some low-fat dairy and lean meats, poultry, fish, and vegetable oil will be high in fiber and lower in saturated fats, trans fats, and dietary cholesterol © 2010 Pearson Education, Inc. Any Questions? © 2010 Pearson Education, Inc.