The Lipids Triglycerides Phospholipids and Sterols Chapter 5 Lecture 2 Dr Alisha Rovner University of Delaware Nutrition Concepts NTDT200 Fall 2013 Lecture Objectives Recognize the chemistry of fatty acids and triglycerides and differences between saturated and unsaturated fats Describe the chemistry food sources and roles of phospholipids and sterols Summarize fat digestion absorption and transport Lecture Objectives Explain the relationships among saturated fat trans fat and cholesterol and chronic diseases noting recommendations Explain the relationships between monounsaturated and polyunsaturated fats and health noting recommendations Lipid Review Family of compounds that include Triglycerides Phosopholipids Sterols Characterized by their insolubility in water Review of Triglycerides Glycerol backbone with 3 fatty acids Predominant lipids in both food and in the body Fatty acids vary in the length of their carbon chains their degrees of unsaturation and the location of their double bonds Important terms to know Fats Oils Fatty acids Saturated fatty acids Unsaturated fatty acids Hydrogenation Trans Fats Phospholipids Unique chemical structure that allow them to be soluble in both fat and water In food industry they are used as emulsifiers eg lecithin In the body they are part of cell membranes help fat soluble substances pass in and out of cells Phospholipids Emulsifiers are substances with both water and fat soluble portions that promote the mixing of oils and fats eg Mayonnaise Without help from emulsifiers fats and water don t mix p136 Phosopholipids Lecithin supplements Claims that it s a major constituent of cell membranes that cell membranes are essential to the integrity of cells therefore people must take a supplement Supplements are NOT necessary because people make all of the lecithin they need not an essential nutrient Large doses can cause GI distress sweating and loss of appetite Sterols Compounds containing a 4 ring carbon structure with any of a variety of side chains attached Sterols in the body include Cholesterol Bile acids Steroid hormones Vitamin D Sterols Cholesterol most familiar sterol Liver makes 800 1500 mg day endogenous Certain foods contain cholesterol exogenous Only animal products contain cholesterol Not inherently evil body needs it Harmful effects in the body occur when it accumulates in the artery walls and contributes to formation of plaque Sterols Fat soluble vitamin D is synthesized from cholesterol Structurally very similar with the exception that cholesterol has a closed ring highlighted in red and vitamin D is open Lipid Digestion Fats are hydrophobic fear of water so there s a challenge in keeping the fats mixed with watery fluids in GI tract Goal of fat digestion is to dismantle triglycerides into smaller molecules monoglycerides fatty acids and glycerol that the body can use Lipid Digestion Mouth Fat digestion starts off slowly here Stomach Churning grinds solids to finer particles mixes chyme and disperses fat into small droplets Gastric lipase hydrolyzes small amount of fat Little fat digestion actually occurs here Lipid Digestion Small intestine When fat enters it triggers release of cholecystokinin CCK to release bile which acts as an emulsifier Fats are fully digested here After bile emulsifies fat it s either reabsorbed or excreted Lipid Absorption The end products of fat digestion are 1 Monoglycerides mostly 2 Fatty acids some 3 Glycerol very little Small molecules short and medium chain fatty acids can move directly into the bloodstream Larger lipids long chain fatty acids combine with bile to form micelles that are water soluble Absorption of Fat Lipid Transport Lipoproteins solve the body s challenge of transporting fats through watery bloodstream Four main types of lipoproteins which can be distinguished by their size and density Chylomicrons Very low density lipoproteins VLDL Low density lipoproteins LDL High density lipoproteins HDL Lipid Transport 4 main types of lipoproteins 1 Chylomicrons transport diet derived lipids from small intestines to the rest of the body 2 Very low density lipoproteins VLDL Lipids made in liver are packaged with proteins and shipped to other parts of body 3 Low density lipoproteins LDL circulates throughout the body and makes their content available to cells of all tissues 4 High density lipoproteins HDL removes cholesterol from the cells Health Implications HDL and LDL Blood cholesterol linked to heart disease is LDL cholesterol bad cholesterol High HDL good cholesterol has protective affect on heart HDL represents cholesterol returning to liver for breakdown and excretion Factors that LDL and or HDL Weight control Consuming mono or poly unsaturated fat rather than saturated fat Soluble dietary fiber Phytochemicals Moderate alcohol consumption Physical activity Desirable blood lipid profiles Blood lipid profiles are blood tests that include total cholesterol triglycerides and various lipoproteins Desirable values Total cholesterol 200 mg dL LDL cholesterol 100 mg dL HDL cholesterol 60 mg dL Triglycerides 150 mg dL Health Effects of Lipids Elevated blood cholesterol major risk for cardiovascular disease CVD Cholesterol accumulates in arteries restricts blood flow and raises blood pressure Blood cholesterol often used to predict a person s likelihood of having a heart attack or stroke Much of the effort to prevent CVD focuses on lowering blood cholesterol Health Effects of Lipids Saturated fats raise LDL cholesterol which increases risk of CVD Major sources of saturated fat in diet are whole milk cream butter cheese ice cream beef tropical oils coconut and palm Simple ways to decrease saturated fat intake are to choose poultry fish fat free milk nonhydrogenated margarines and unsaturated cooking oils Health Effects of Lipids Association between trans fats and CVD Alter blood cholesterol the same way saturated fats do Found in pastries deep fried foods chips Many restaurants and food manufacturers have eliminated or greatly reduced this type of fat Benefits from Mono and Polyunsaturated fats Replacing saturated and trans fats with mono and polyunsaturated fats are most effective dietary strategy in preventing CVD Lower rates of CVD among people in the Mediterranean is often attributed to their liberal use of olive oil Benefits from Omega 3 fats Regular consumption of omega 3 PUFAs Prevent blood clots Protect against irregular heartbeats Lower blood pressure Fatty fishes are among the best
View Full Document
Unlocking...