Lipids 1 (2014)_Stream[Compatibility Mode]

151.232 2014 (Lipids 1) 1

Lipids

151.232Dr Cheryl Gammon

2014

IFNHH, AlbanyMassey University

Lipids 1Learning outcomes:

By the end of this session you should be able to: Define the functions of lipids in the human body and

in food Differentiate between different types of lipids

according to their chemical structure, classification and food sources

Describe the digestion, absorption, transport and metabolism of lipids

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IntroductionFat plays critical role in health and functioning of human body: Source of energy (37kJ/g / 9kcal/g) Insulates body from temperature extremes Cushion vital organs to protect from mechanical

shock Carriers of fat soluble vitamins A, D, E, K Important structural component of cell membranes Play role in cell signaling Precursors for synthesis of hormones and other

important physiological mediators

Introduction (cont)

In food, lipids contribute to aroma, flavour, textureHowever, over-consumption associated with chronic disease (CHD, obesity, cancer)Focus over last decades to decrease dietary fat intakeIs less fat better?

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Introduction (cont)Recent research has shown that very low fat diets will not necessarily chronic disease.Very low-fat diets (60%E) possible adverse effects

Introduction (cont)Different types of fatty acids or fatty food sources different physiological effects.Risk for chronic disease depend on quality rather than quantify of dietary fat.E.g. replacing saturated fatty acids (SFA) with unsaturated fatty acids more effective in CHD risk than by total fat intake.

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LipidsTriglycerides (triacylglycerols) Fats and oils (95%) Human body (99%)

Phospholipids

Sterols

Copyright 2005 Wadsworth Group, a division of Thomson Learning

White Adipose TissueWhite (yellow) adipose tissue (WAT)Stores triacylglycerols.Storage stimulated by insulin / reported by leptin.Catecholamines (adrenaline, noradrenaline) and glucagon:

activate lipolysis FFAs bloodUsed for energy by other tissues (mainly muscle tissue).Number and sites of adipocytes dependent on genetic predisposition and feeding habits.

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White adipose tissue

Brown Adipose tissue (BAT)Metabolically highly active and different from WAT.Regulated by catecholamines and adrenergic (sympathetic) nerves via adrenoreceptors.Especially active in hibernating animals and human babies.Essential to body temperature maintenance in small mammals.In humans and other large mammals, BAT mostly disappears after infancy.Exposure to cold or excess food energy intake (cafeteria diet) leads to fatty acid catabolism (oxidation of fatty acids).BAT produces heat (uncoupling proteins) instead of ATP and gives significant rise in body temperature.

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Brown adipose tissue

Transgenic Mice expressing human Uncoupling Protein 3 (UCP3).

Mice ate 15 - 54% more than controlsFat-tissue mass 44 - 57% less than controls.Cholesterol levels 70% loweri.e. able to eat more than normal but still weigh less due to increased fat metabolism.

UCP-3 is one possible drug target for obesity research. no side effects from the increased UCP3 greater insulin sensitivity

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Triglyceridesglycerol + 3 fatty acids triglyceride + H2OProperties depends on constituent fatty acids

Fatty Acids


Saturated (Stearic acid 18:0)

Simplified structure

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Fatty AcidsLengthSaturated vs unsaturatedLocation of double bonds (omega number)Configuration of double bonds (shape)


Fatty AcidsLength of carbon chain Short chain (14 carbons) (most common in diet)

Shorter more soluble in water

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Fatty AcidsDegree of saturation Saturated fatty acid Monounsaturated fatty acid Polyunsaturated fatty acid

An impossible chemical structure

Monounsaturated (Oleic acid 18:1)

Polyunsaturated (Linoleic acid 18:2)

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Degree of saturation affects firmness of food products at room temperature

Fatty AcidsLocation of double bonds Omega number

Omega-3 fatty acidOmega-6 fatty acid


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Polyunsaturated fatty acids

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Dietary sources of SFA

Animal products (butter, meat, poultry, full-fat dairy products, plant oils (coconut, palm, palm kernel)

Palm kernel vs palm: Palm kernel - 82% SFA Palm - 50% SFA,

50% UFA (MUFA)

MUFA:Olives, olive oil, canola, nuts, avocado, rice bran oil (43%)

PUFA:N-6 (linoleic acid): sunflower oil, PUFA margarine, soybean, nuts, corn oil, cotonseed oil, rice bran oil (39%), grapeseed oil, sunflower seeds, pumpkin seeds, etc. Gamma-linolenic acid: evening primrose, borage, blackcurrant seed oilN-3: plant sources (ALA) = soybean, canola, flaxseed (linseed), walnuts, Chia seedsFish sources (EPA, DHA) = mackerel, pilchards, salmon, sardines, herring, kipper, farmed kingfish, snapper, grey mullet, kahawai, Jack mackerel, squid, mussels, eelMarine algae (rich source of DHA)

n-3 fortified products = eggs, milk, spreads, bread

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Fatty acid composition of some fats & oils

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Other sources: fish oil and algal oil supplements

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Characteristics of fats in food

Degree of unsaturation Firmness at room

temp (liquid/solid) Stability

Oxidation Antioxidants Hydrogenation



Hydrogenation

Chemical process of adding H to unsat. FA to make it more solid and stable

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Trans fatty acids

Food manufacturers rarely use total hydrogenation and fat is partially hydrogenated yielding trans fatty acidsE.g. shortening, margarine

Small amounts of trans fats also found in animal products due to bio-hydrogenationUnsaturated health benefits lostAssociated with CHD risk important to decrease / eliminate from food supply


Trans fatty acids

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Food sources of trans FADeep-fried foods (vegetable shortenings)Cakes, cookies, doughnuts, pastry, crackers, snack chipsMargarine / spreadsMeat and dairy products (via bio hydrogenation)In NZ: 0.6%E (WHO recommendation 85% intakes below 1% 75% from ruminant foods High consumers (>1%): greatest contribution from

pastry products, creamy style pasta dishes, cheese, popcorn, doughnuts, take away fish products

Alternatives to hydrogenation

Edible fats suitable for use by food industry need to be solid or semi-solid at room temperature. People demand optimal taste, flavor, texture, shelf-stability, convenience, novelty as well as healthy products.Two possibilities: Interesterification Blending of natural saturated fatty acids

with unsaturated fatty acids

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Alternatives to hydrogenationInteresterification = randomisation of the fatty acid positional distribution along the glycerol backbone of the TG molecule

1) 31% C16:0

2) 9% C16:0

3) 31% C16:0

1) 23% C16:0

2) 25% C16:0

3) 23% C16:0

Palm oil Inter-esterified palm oil

Interesterification

No trans fatty acids introducedFatty acid composition stays the same. IE modify melting and crystallisation properties of fats & oils mixtures - resulting in desired functional properties. Process already chosen as route of choice for some food manufacturers. Trans-free spreads in NZ

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Palm-stearin

Palmkernel oil

Coconut oil

Fully hydrogenated oils (high in C18:0)

Soy bean oil

Sunflower oil

Corn oil

Solid fat Liquid oil

+

IE

Blending: Blending of unsaturated fat sources with

natural SFA rich oils such as palm oil.

Phospholipids


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PhospholipidsSimilar to TG but contain phosphorousWater soluble head & fat-soluble tailComponent of cell membranes. Regulates transport of substances in & out of cellsServe as emulsifiers (allow fat & water to mix and travel in and out of cells)Lecithin often used as emulsifier in foodEgg yolks, peanuts, soybeansBody manufactures. Thus not essential.


CholesterolAnimal productsRoles of cholesterol Bile acids Sex hormones

(estrogen & testosterone)

Adrenal hormones Vitamin D Structural component

of cell membrane Body makes own

cholesterol.Copyright 2005 Wadsworth Group, a division of Thomson Learning

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Cell membrane function depends upon maintenance of their lipid composition

Less fluid at lower temperature cholesterol opposes

Fluidity depends upon contentof unsaturated FAs

Plant sterols

Naturally occurring in plants (vegetable oils, seeds, nuts)Not well absorbedFunctional food Decrease blood

cholesterol

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Dietary fat Triglycerides(Fatty acids)

Saturated fatty acids

UnsaturatedFatty acids

Trans Monounsaturated Polyunsaturated

Omega-3 Omega-6

= + Sterols Phospholipids+95% 5%

Fat DigestionMouthMelting when body temp reachedLingual lipase

Small role in adultsActive role in infants (digest short & medium-chain fatty acids in milk)Little lipid digestion


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Fat DigestionStomachChurning and mixing fat with water

and acidGastric lipase (primarily on SCFA)Little lipid digestion


Fat DigestionSmall intestine (most of the digestion)Cholecystokinin (CCK) causes

gallbladder to contract and releaseBile - emulsification


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Fat Digestion


Bile = bile salts made from cholesterol + lecithin + other phospholipids + electrolytes (Na, K, Cl, Ca)

Fat Digestion


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Fat DigestionHydrolysisTriglycerides monoglycerides +

2 free fatty acids

Phospholipids lyso-phospholipid + 1 free fatty acid

Cholesterolesters free cholesterol + 1 free fatty acid


Pancreatic+ intestinal lipase

Phospholipase

CE-hydrolyse

Fat Digestion


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Fat DigestionOverview


Fat DigestionEnterohepatic circulationHow viscous fiber decrease cholesterol


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Copyright 2005 Wadsworth Group a division of Thomson Learning

Lipid Transport to tissueLipoproteins hydrophobic lipid core, lipophilic/protein surface4 major classes (categorised by function & density)ChylomicronsVLDL = very-low-density lipoproteins LDL = low-density lipoproteinsHDL = high-density lipoproteins


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Lipid Transport

Apolipoproteins

Important role in lipid metabolism: Ligand for chylomicron & LDL-receptor (apoE,

apoB100) Activator of enzymes (lipases) (apoA-I, apoC-II) Give structure (apoA-II) Mediates lipoprotein formation (apoB48, apoB100)

Apolipoprotein profile genetically determinedGenetic variants may result in specific metabolic disorders (e.g. APOE polymorphisms)

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Receptor mediated uptake of cholesterol and cellular cholesterol homeostasis

Cholesterol LDL-R synthesis HMGCoA reductase cholesterol synthesis Activation of ACAT storage of excess CE

HMGCoA: Hydroxymethyl-glutaryl-CoA; ACAT: Acyl CoA:cholesterol acyltransferase

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Reference values for lipid profiles

TC

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Micelle

Bile

Dietary cholesterol

Chrystals

Faeces

Plant sterols

Plant Sterols: Mechanism of action (continue) Consequences for cholesterol metabolism

LDL-receptors:* uptake from circulation* serum TC & LDLC

Liver compensate: cholesterol synthesis(HMG-CoA reductase)* LDL-receptors

Reduced absorption:Lower liver [cholesterol]

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Regulation of fat storage & oxidation

FA circulate in blood in form of NEFA bound to albumin As TG in lipoproteins Ketone bodies (prolonged starvation)

Storing of fat Fat is stored as TG Provides 37kJ/g Unlimited capacity unlike glycogen stores LPL (on surface of adipose cells) hydrolyse TG in

lipoproteins to fatty acids & glycerol and passes into cells.

In cell TG are again formed for storage. Adipose cells always stores fat after meals. Later

released when needed (fasting).

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Making fat from CHO or protein Excess CHO & protein can be stored as fat FA can be made from CHO and amino acids

not vice versa FA preferred fuel for oxidation whenever

circulating concentrations are high (fasting) and glucose is spared.

Making fat from fat: Body simply absorbs the parts and puts them

together again in storage. Requires very little energy. To convert CHO to fat requires more energy.

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Using fat as energy Fat supplies 60% of bodys ongoing energy needs

during rest. During prolonged exercise or extended periods of

food deprivation greater supply of energy. FA stored as TG in adipose tissue mobilised by

action of hormone sensitive lipase (HSL). HSL hydrolyse stored TG into FA & glycerol and

release in circulation. Oxidation regulated by availability of FA and rate of

utilisation which in turn is dictated by insulin:glucagon

Fasting /exercise - insulin - HSL (break down of TG in adipose tissue) - NEFA in circulation.Ingestion of food - insulin - LPL, HSL -lipolysis, esterification of FA in adipose tissue (TG).

TG in chylomicron/VLDL

Fatty acids + glycerol

LPL

TG

Fat cell

Fatty acids + glycerol

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Lipids 1 (2014)_Stream[Compatibility Mode]