The Macronutrients - Lipids Chapter 1

Lipids  Lipid is a general term for a heterogeneous group of compounds. Oils, fats, waxes, and related compounds Simple lipids Compound lipids Derived lipids

Lipids Functions  Provide energy  Protect vital organs  Provide insulation from the cold  Transport the fat-soluble vitamins A, D, E, and K

Lipids  Simple lipids Neutral fats – consist primarily of triacylglycerols Triglycerides Major storage form of fat in adipose cells

Triglycerides C,H,O Composed of 3 fatty acids (FA) Glycerol molecule TG vary in the type of FA and their bonding pattern FA vary in the number and arrangement of double bonds Usually even number C

Acetic Acid

Triglyceride

Fatty Acids  Saturated fatty acids  Single covalent bonds between carbon atoms  Covalent bonds share electrons  All of the remaining bonds attach to hydrogen.

Fatty Acids  Unsaturated fatty acids  One or more double bonds along the main carbon chain. Monounsaturated fatty acid - one double bond. Polyunsaturated fatty acid - two or more double bonds.

Fatty Acids Stearic acid, an 18-carbon saturated fatty acid

Fatty Acids Oleic acid, an 18-carbon monounsaturated fatty acid

Lipids Stability Oxygen exposure causes spoilage-rancid PUFA’s spoil more easily Increase saturation Hydrogenation Prolongs shelf life – prevents oxidation Alters texture – liquids → solids

Hydrogenation

Trans-Fatty Acids Changed from cis to trans configuration and act like saturated fats in the body Partial hydrogenation Higher melting point

Trans-Fatty Acids

Dietary Lipids Typical daily intake (< 30% total kcals) Should consist of: 65% animal lipids 35% vegetable lipids <10% saturated Little or no trans fat

Essential Fatty Acids Double bonds Omega number Position of first double bond Omega-3 FA – 3 rd position Linolenic acid Omega-6 FA – 6 th position Linoleic acid Body can only make double bonds after the 9th carbon from the omega end

Linolenic Acid – omega-3

Fatty Acids-omega-6 Linoleic acid, an 18-carbon polyunsaturated fatty acid

Essential Fatty Acids Functions Immune function, Vision Cell membrane, and Production of hormone-like compounds

Essential Fatty Acids Omega-3 Omega 6 Alpha-linolenic acid Linolenic acid DHA EPA Arachidonic Acid (docosahexanoic (eicosapentaenoic acid) acid)

Essential Fatty Acids DHA, EPA Decrease blood clotting Care must be taking when supplementing DHA, EPA when on anticoagulant medication Or when having surgery Reduce heart attacks Fish oils have an anti-arrhythmic effect on myocardial tissue. Decrease inflammation, pain

Compound Lipids Phospholipids Built on a glycerol backbone One or more FA Phosphorus group Nitrogenous base Found in body, cell structures Synthesized by the body as needed liver Not needed in diet, not essential

Compound Lipids Phospholipids Contain polar head groups Hydrophilic head (protein) Hydrophobic tail (two FA chains) Allows for movement of fat soluble substances Vitamins Hormones

Phospholipids

Compound Lipids Phospholipids Lecithin - 5% of lipids in diet Eggs Liver Soybeans Wheat germ Peanuts

Compound Lipids  Glycolipids:  Fatty acid bound with carbohydrate and nitrogen  Essential part of cell membranes

Glycolipids

Compound Lipids  Lipoproteins:  Proteins joined with triacylglycerols or phospholipids  Primary method of lipid transport

High, Low-Density Lipoprotein Cholesterol 5 types of lipoproteins exist Based on gravitational density Chylomicrons, VLDL, IDL, LDL and HDL Chylomicrons – fat droplets Long chain triacylglycerols Phospholipids Free fatty acids A,D,E,K

Chylomicron

Compound Lipids Lipoproteins Very low density lipoprotein (VLDL) Formed in liver 95% fat (60% triacylglycerol) Transports triacylglycerols to muscle, adipose Oxidation of VLDL and uptake of triglycerides into cell (lipoprotein lipase)

Compound Lipids Lipoproteins Low density lipoprotein (LDL) Contain less lipid than VLDL Carry most of the cholesterol (60-80%) Great attraction to cells of arterial walls

Cholesterol Lipoproteins High density lipoproteins Scavenger Reverse transport of cholesterol Delivers cholesterol to liver Bile Excretion through intestinal tract

Cholesterol Exogenous Dietary cholesterol (300 mg) Endogenous Cellular synthesis (70% in liver) 0.5 to 2.0 g/day Sufficient for body’s needs