What Are Lipids? Chapter 5 Lipids: Not Just Fat BIOL 103 SP2017 EssenBal nutrients Provide energy Help transport fat- soluble nutrients throughout the body Contribute greatly to the flavor and texture of food Lipids Include Triglycerides (most abundant lipids) In body: stored in adipose Bssue In food: fats and oils Phospholipids (~2% of dietary lipids) Plant and animal origin Body can make them Soluble in fat and water Sterols (very, very small % of lipids) Most well known: Cholesterol Fa\y Acids Are Key Building Blocks Fa\y acid Determines whether a fat is or at room temperature Basic structure: (-COOH); (-CH 3 ) 1
Fa\y Acids Are Key Building Blocks Chain length Fa\y acids differ in chain Lengths vary from 4 to 24 carbons Grouped as short- chain, medium- chain, and long- chain Fa\y Acids Are Key Building Blocks Chain Length Shorter fa\y acids remain at room temperature and even with refrigerabon Shorter fa\y acids also are more - soluble Fa\y Acids Are Key Building Blocks SaturaBon Saturated fa.y acids All bonds between carbons Unsaturated fa.y acids One or more carbon bonds is a bond 1. Monounsaturated fa.y acid (MUFA) 2. Polyunsaturated fa.y acid (PUFA) Fats with more double bonds are generally more 2
Saturated vs. Unsaturated Fat Fa\y Acids Are Key Building Blocks Cis vs. trans Unsaturated fa\y acids can vary in shape Cis fa.y acids Chain is Occur naturally Trans fa.y acids Chain is straighter Produced by Saturated vs. Unsaturated/Cis vs. Unsatruated/Trans Fats 3
Trans Fat In health, trans fa\y acids are known to raise LDL ( bad ) cholesterol, and lower HDL ( good cholesterol ), promote systemic inflammabon, and increase triglycerides in your blood. History and how it is made: In Europe (1910): needed a cheaper bu\er subsbtute for soldiers In US (1960s): People wanted to eat a healthier and cheaper bu\er à food scienbsts decided to hydrogenate vegetable oil to solidify them What are the posibve and negabve consequences of hydrogenabng a fat? OxidaBon causes food to spoil and damage body Bssues Pros Cons 1. Longer shelf life 2. Improved texture and taste 1. More saturated fat 2. Creates trans fat Fa\y Acids are Key Building Blocks NonessenBal and essenbal fa\y acids 1. NonessenBal fa.y acids Can be made in the body Not essenbal to have in your diet Fa\y Acids Are Key Building Blocks EssenBal and NonessenBal Fa\y Acids 2. EssenBal fa.y acids Must come from food Cannot be made by the body Two families: Omega- 3 (alpha- linolenic acid) Omega- 6 (linoleic acid) Pre- cursors to eicosanoids 4
Structure Glycerol + 3 fa\y acids Most fa\y acids exist as part of triglyceride molecules Triglycerides Triglycerides Apple vs. Pear FuncBons 1. Energy source: 9 kcal/g 2. Energy reserve: form of stored energy in adipose Bssue 3. InsulaBon and protecbon: 1. Visceral fat 2. Subcutaneous fat 4. Carrier of fat- soluble nutrients 5. Sensory qualibes (flavor, odor, texture) in food 5
Triglycerides in Food Found in a variety of fats and oils Classified by their most prevalent type Saturated fa\y acids: foods and tropical oils Polyunsaturated fa\y acids: plant or animal based Omega- 3: soybean, flaxseed oils; salmon, tuna Omega- 6: seeds, nuts, corn oil, meat, poultry, eggs Phospholipids Structure Glycerol + two fa\y acids + phosphate group CompaBble with both fat and water: ideal emulsifier Keep fat suspended in water Keep oil and water mixed Phospholipids FuncBons 1. Perfect element for cell membranes Able to communicate with watery environments of blood and cell fluids SelecBvely allow both fa\y and water- soluble substances into the cell Store fa\y acids temporarily 6
Phospholipids FuncBons 2. Role in Fat DigesBon and Transport Mouth and Stomach Break fats into Bny parbcles for digesbon IntesBne ConBnue emulsifying fat Blood Coat the surface of the lipoproteins that carry lipid parbcles to their desbnabons in the body Phospholipids FuncBons Emulsifiers ( ) in the human body Lecithin is a phospholipid with choline Role: Forms which are used to emulsify fats during digesbons Phospholipids FuncBons Phospholipids in Food Emulsifier (lecithin) in food industry Lecithin is a blend of phospholipids with different nitrogen- containing compounds FuncBon: Used as an emulsifier to combine two ingredients that don t ordinarily mix, such as oil and water (e.g. salad dressing) Can be used in high- fat powered products (e.g. dry milk, coffee creamers, milk replacers) helps mix fa\y compounds with water Soy Lecithin: creaminess, longer shelf life, soqeners, anb- sbckiness Occur naturally in plants and animals, but in much smaller amounts than triglycerides Abundant in egg yolks, liver, soybeans, peanuts Not a dietary essenbal (since our body can make it) 7
A category of lipids that include cholesterol Structural characterisbcs: MulBple ring structure Contain no fa\y acids Sterols Sterols Cholesterol funcbons: 1. Structural component of cell membranes 2. Precursor to other substances Examples: Vitamin D, Sterol Hormones, bile salts Cholesterol synthesis in Sterols in food Found in animal and plant foods Does Plant Sterols Help Reduce Blood Cholesterol? 8
Lipid DigesBon and AbsorpBon DigesBon of Triglycerides and Phospholipids Mouth Chewing and lingual lipase Stomach Breaks triglycerides via gastric lipase down to diglycerides and free fa\y acids Small intesbne Bile and pancreabc lipase emulsify and break down the fats for absorpbon IntesBnal cells absorb glycerol and short- chain fa\y acids into the bloodstream Lipid DigesBon and AbsorpBon Lipid DigesBon Small IntesBne (cont.) Bile salts form micelles (water- soluble globules with a fa\y core) to carry long chain fa\y acids to the microvilli Bile salts return to the to be used again Enterohepa1c Circula1on 9
Lipid AbsorpBon To travel in the bloodstream, lipids are packaged into carriers Lipoprotein leave the intesbnal cell as Deliver dietary lipids from intesbnes to cells and liver Chylomicron goes to lymph system (lacteals) à bloodstream TransportaBon of Lipids in the Body Lipids packaged into lipoprotein carriers in order to travel in the bloodstream Lipoproteins differ by size, density, and the composibon of their lipid cores: VLDL IDL LDL HDL Lipids in the Body 1. Very- low- density lipoproteins (VLDL): Deliver to cells 2. Intermediate- density lipoproteins (IDL) Returns to liver and is converted to LDL 3. Low- density lipoproteins (LDL) Deliver to cells, which body uses to synthesize membranes, hormones, etc. Returns to liver aqerwards 4. High- density lipoproteins (HDL) Pick up cholesterol for removal or recycling 10
Lipoprotein Pathway Summary OpBmal Levels of Cholesterol RecommendaBons for Fat Intake Recommended intake Reduce saturated fat, trans fat, and cholesterol Total fat: 20 35% of calories Less than 10% of calories from saturated fat 2010 Guidelines: Less than 300 mg per day of cholesterol RecommendaBons for Fat Intake EssenBal fa\y acid requirements Linoleic acid/omega- 6 fa\y acids should provide about 2% of calories Requirements for omega 3 fa\y acid is less well known Omega- 6 and omega- 3 balance RaBo of omega- 6 to omega- 3 fa\y acids Why would it be bad to consume too much omega 3 fa\y acids? 11
RecommendaBons for Fat Intake Role of fat replacers Different types of composibon Olestra: Sucrose + fa\y acids IndigesBble provides no calories Reduces absorpbon of fat- soluble vitamins 1. Heart disease/cardiovascular Diseae Leading cause of death in US (1 death/ minute) Major risk factors: High blood cholesterol Smoking High blood pressure 2. Obesity Determined by excessive accumulabon of body fat leading to a body weight in relabon to height that is significantly greater than some accepted standard. High- fat diets promote weight gain Significant within the U.S. populabon 34.9% of American adults 17% of American children and adolescents 12
3. Metabolic syndrome Affects ¼ of American adults Cluster of at least three symptoms: Excess abdominal fat High blood glucose High serum triglycerides Low HDL cholesterol High blood pressure 4. Cancer Results from complex mix of lifestyle, hereditary, and environmental factors Role of nutribon and diet complex Evidence suggests 30-40% are due to poor food choices and physical inacbvity Some dietary factors act as promoters, while others serve a protecbve role Cancer Dietary and lifestyle factors for reducing cancer risk Maintain a healthful weight Adopt a physically acbve lifestyle Consume a healthy diet Limit alcohol consumpbon Reducing heart disease risk AHA diet and lifestyle recommendabons Consume an overall healthy diet Aim for a healthy body weight Aim for a desirable lipid profile Aim for normal blood pressure Aim for normal blood glucose levels Be physically acbve Avoid use of and exposure to tobacco products 13
Reducing heart disease risk AHA recommendabons Balance calorie intake and physical acbvity to achieve or maintain a healthy body weight Consume a diet rich in fruits and vegetables Choose whole- grain, high- fiber foods Consume fish, especially oily fish, at least twice a week Limit your intake of saturated and trans fat and cholesterol Reducing heart disease risk AHA recommendabons (cont.) Minimize your intake of beverages and foods with added sugars Choose and prepare foods with li\le of no salt If you consume alcohol, do so in moderabon Follow the AHA recommendabons when eabng outside of the home Puvng It All Together Healthy People 2020 objecbves target reducing deaths from heart disease and stroke and reducing the number of adults with high blood cholesterol levels 14