Fats

What Are Fats/Lipids? Organic substances that are relatively insoluble in water and soluble in organic solvents

Usefulness of Fats in the Body Energy stores Padding Insulation Cell membranes Raw materials

Usefulness of Fats in Food Essential nutrient Energy Carriers Taste & smell Satiety Texture

Major Lipid Classes Triglycerides Fatty acids Phospholipids Sterols

Triglycerides Structure –Glycerol molecule –3 fatty acids (FA’s) Most fatty acids in body and in food are found in form of triglycerides Function –Energy production 9 kcal/g FA’s used to produce ketones –Insulation, padding, essential fatty acids

The Structure of a Triglyceride

Structure of Fatty Acids Fatty acid consists of: Chain of carbon atoms –Most common FA’s have 18 carbons Carboxylic acid group Methyl group

Structure & Classification of Fatty Acids Classification based on structure –Saturated (no double bonds) –Unsaturated Monounsaturated (1 double bond) Polyunsaturated (multiple double bonds) Structure Affects: –Physical & Chemical properties –Physiologic functions

Common Names

Trans Fatty Acids Shape of molecule related to position of hydrogen Cis configuration most common in nature Trans double bond results from process of hydrogenation Physical & physiologic properties

The Essential Fatty Acids:  Linoleic Acid –Omega-6 fatty acid –Can be made into arachidonic acid  Linolenic Acid –Omega-3 fatty acid EPA & DHA are omega-3 FA’s found in fish and human breast milk  Body cannot produce, must come from diet

©2001 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license. Omega-3 and Omega-6 Fatty Acids Compared

Functions of the Essential Fatty Acids Used to make eicosanoids –Eicosanoids = hormone-like Muscle relaxation/contraction Blood vessel dilation/constriction Blood clotting Immune response – fever, inflammation, pain Structure of cell membranes Gene regulation Skin – protect against water loss

Ratio of Fatty Acids in Selected Foods

Significant Food Sources of Fatty Acids Saturated – meat, pork, dairy products Trans - shortening, margarine, crackers, pastries, bakery products, “hydrogenated oil” Polyunsaturated – vegetable oils, nuts Monounsaturated – nuts, seeds, avocados, fish, olives Omega-3’s – oily fish, walnuts, canola oil, flax seed

Phospholipids Major components of cell membranes Play roles in digestion, absorption, transport of lipids, cellular metabolism Structure - Hydrophilic and hydrophobic portions

Phospholipids are Components of Cell Membranes

Sources of Phospholipids Found naturally in most foods Phosphatidylcholine –Common name “lecithin” –Egg yolks –Emulsifier in foods Ex: mayonnaise doesn’t separate like salad dressing

Sterols Large, complex molecules of connected rings of carbons with C, H, & O attached Vitamin D Cholesterol –Component of cell membranes –Makes sex hormones –Makes bile, an emulsifier in digestion

Cholesterol

Sources of Cholesterol in the Body: Synthesis & Diet Cholesterol NOT essential in diet, body makes Food – only in animal sources Diet + genetics influences cholesterol synthesis Saturated FA’s impact cholesterol production most significantly

Foods with Cholesterol

Digestion of Dietary Lipids Mouth & Stomach – lipases begin lipid breakdown Small intestine – main site of digestion –Emulsification by bile –Enzymes cleave FA’s from glycerol –FA’s absorbed by intestinal villi Small FA’s transported to bloodstream Large FA’s reassembled into TG’s and transported by chylomicrons

Chylomicrons –Made by intestines Lipoproteins –Made by liver Function –Transport lipids Chylomicrons & Lipoproteins

Very-Low-Density Lipoproteins (VLDLs) Made by liver Contains large amounts of triglyceride Delivers fatty acids to cells More protein-dense than chylomicrons

Intermediate-Density Lipoproteins (IDL) Lipoprotein that results from loss of fatty acids from VLDL Taken up by liver or remain in circulation Converted to low-density lipoproteins (LDLs)

Low-Density Lipoproteins (LDLs) “Bad” cholesterol Delivers cholesterol to cells Can increase build-up of plaque High levels of LDL associated with increased risk for cardiovascular disease

High-Density Lipoproteins (HDLs) “Good” cholesterol Made by liver Circulates in the blood to collect excess cholesterol from cells Returns cholesterol to liver for excretion in bile Highest protein content

Overview of Lipoproteins

Factors Impacting LDL Levels Increase LDL –SFAs –Trans fatty acids –High cholesterol intake –Lifestyle factors –Genetics Decrease LDL –High-PUFA diet –Ω-3 fatty acids –Dietary fiber –Lifestyle factors –Genetics

Factors Impacting HDL Levels Increase HDL –High MUFA intake –Moderate alcohol consumption –Lifestyle factors – exercise Decrease HDL –Trans fat High carbohydrate intake may decrease HDL, unclear if low-carbohydrate diet offers protection Genetic factors influence HDL

Using Lipids for Energy Lipolysis Stimulated by: –Low levels of insulin during hypoglycemia –Exercise –Physiological stress Utilized aerobically

Storing Lipids as an Energy Reserve Energy excess Insulin stimulates triglyceride storage Lipogenesis (Synthesis of fatty acids & triglycerides)

American Heart Association 2006 Recommendations for CVD Risk Reduction Eat 2 servings of fish high in ω-3 fatty acids/week Cholesterol <300 mg/d SFA < 7 % of kcals/d (U.S. Dietary Guidelines <10%) Trans fat <1% of kcals/d

Choosing a Diet Balanced in Fats Select lean meats –“loin” or “round” cuts of beef, pork Choose low-fat dairy Replace SFA with PUFA and MUFA –Ex: oil instead of butter, nuts instead of chips Eat enough, but not too much, total fat –20-35% kcal from fat (IOM Natl Acad of Sci)