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

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

atomsCovalent 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

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 – 3rd position

• Linolenic acid

• Omega-6 FA – 6th 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