Lipids in human nutrition

LFN 1232Prof. Chandrani Liyanage

Fat isA heterogeneous mixture of lipidsPredominantly triglycerides (95%), and phospholipids(small proportion), glycolipids and sterolsStored mainly as triglycerides in fat stores and esters of fatty acids (saturated & unsaturated) and glycerolImportant in providing insulation against cold

Principal dietary sources of fatDairy productsCooking oils and fats Margarine, butter and other fatsMeatShell fishEggsBiscuitsCakes and sweet meatsPastries and other snacksNuts and some grains

Many foods contain structural fats, phospholipids and glycolipids, cholesterol and plant sterolsEggs contain saturated and monounsaturated fatty acids, lipoprotein, triglycerols, cholesterol and phospholipidsBrain as a food provides animal sphingolipidsDairy products contain milk fat globule membranesGreen leafy veg contain galactolipidsCereals, grains, vegetables and fruits contain membrane lipids

Fatty acidsAre chains of hydrocarbons with the carboxyl (acid) functional group (COOH) at one end of the chain and a methyl group (CH3) at the opposite endDetermine the characteristics or the properties of the fatAre different - in their length of the carbon chain saturation liquid or solid state at room temp stability and spoilage

Length of the carbon chainShort chains are more solubleShort chains are more easily broken downShort chains are less denseShort chains oxidize more easily (become rancid)Shortest chain found in Butyric acid (in butter) with 4 carbonsFatty acids have even number of carbons (from 4-26) most are 14-18

SaturationEach C within the chain has 2 places for bonds with H (C has 4 bonds and 2 are to the adjacent Cs)If each C has 2 H atoms the fatty acid is saturatedIf 2 C atoms are double bonded to each other it is mono unsaturated having less H atomsIf more than 2 C atoms are unsaturated the fatty acid is poly unsaturatedMost plant fats are unsaturated but fats of tropical plants are saturatedFish oils are unsaturated, animal fats are saturated

Saturated fatty acids Have straight chain structures with an even number of C atomsNumber of C atoms can be 2-30 or more in naturally occurring lipidsUnsaturated fatty acidsContain double bondsHave nutritional and biological importanceRemoval of double bonds results in ethylenic double bonds which are unsaturatedTwo types, cis (hydrogens on the same side)or trans (hydrogens on opposite)

Monounsaturated only one double bondPolyunsaturated two or more double bondsUnsaturated fats with one or more cis double bonds are more common in natural lipids than are transPolyunsaturated fats are susceptible to oxidation but are protected by natural antioxidants (vit E)

Liquid or solid stateShort chain and unsaturated fatty acids are liquid at room temp. The molecules are less dense when they are smaller. The double bonds distort the molecules so that they dont fit togetherSaturated chains are solid (dense) because the fatty acid chains fit together better

Stability and spoilageUnsaturated fats - oxidize more readily, - they have shorter shelf life, - spoilage is quicker, - more easily absorbed

How to deal with spoilage?Important in food industryBy using antioxidants such as butyrate hydroxytolulene, butyrate hydroxyanisole,, propyl gallate, Vit C and Vit AThrough hydrogenation a chemical process that adds H to fatty acid chain - vegetable oils are hydrogenated especially shortenings and margarine to make them solid - hydrogenation forms Trans fatty acids that may not be effectively used by the body

ContdTrans fatty acids have similar effects of saturated fats in the body. Therefore, intake has to be restricted. Partially hydrogenated is a term used in many snacks and margarinesHydrogenation raises the temp. Oil will smoke and oil smoke affects structure producing harmful by products. This accumulates when fats are reused in cooking. Therefore, more refined and less polyunsaturated fats are better for cookingHydrogenation is not always necessary, saturated hard fat can be mixed with unsaturated fat to obtain desired hardness. But this process does not prevent oxidation

ContdRefrigeration to retard oxidation in cold temp.May cause crystallization of fat molecules that affects the texture of foods prepared with fats

Essential fatty acidsOf the 40 different fatty acids, 2 are essential and need to include those 2 in our diets (at least 3% should be of essential)Majority of fatty acids can be converted to fatty acids needed by the bodySome fatty acids interconversions require Vit B6Eczematous dermatitis can occur due to poor intake of essential fatty acids, commonly seen in childrenTwo groups of poly unsaturated fats are essential, omega-3 and omega-6 .

Omega () fatty acidsLinolenic (-6) with 18 Cs and 2 double bondsArachidonic (-6) 20 Cs and 4 double bondsLinolenic (-3) 18 Cs and 3 double bondsEicosopentaenoic (EPA) (-3) 20 Cs and 5 double bondsDocosahexanoic (DHA) 22 Cs and 6 double bonds

Linolenic ( -3) and linoleic ( -6) Are not converted or manufactured these long chain fatty acids from other fatty foods. Therefore, best to have reserves of the specific fatty acids needed.Fairly common in plant oilsEPA and DHA are common in cold water fatty fishLinolenic acid is found in seed oils (walnut,l inseed or flax)

Why important?Essential fatty acids and their longer chain molecular products are necessary for maintenance of growth, good health and reproduction, permeability of the biological membranes to water sugars and metal ions, eicosanoid synthesisAll EFAs are poly unsaturated fats , but all polyunsaturated fats are not essentialEFA activity depends on the presence of a cis-9, cis-12 methylene-interruped double bond system

Our diets are typically high in omega-6 fatty acids but low in omega-3 fatty acids. Therefore, increasing the intake of omega-3 fatty acids may help to - lower serum cholesterol and triglycerides - Raise HDL levels - Reduce arthrosclerosis - lower cancer risks - Reduce inflammatory responses, arthritis pains

Other lipidsPhospholipids - - are modified triglycerides and major component of all membrane cells. Cell membranes are structured from a phospholipid bilayer. Most common phospholipid is lecithin in which molecule choline is attached to the phosphate portion. Choline is also a component of the neurotransmitter chemical , acetylcholine. - are useful emulsifiers particularly in food products - are composed of a glycerol molecule with 2 fatty acids attached by ester bonds and a highly polar phosphate containing cpd attached to the 3rd C. - are not essential nutrients. Can be manufactured by the liver from any fats eaten - All non-processed foods have phospholipids as a part of the cell structure. - Ingested phospholipids are digested to glycerol, fatty acids and phosphate cpds.