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DNT 200NUTRITION FOR HEALTH

SCIENCES

LIPIDS

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DNT 200NUTRITION FOR HEALTH

SCIENCES

Everything I want is either illegal, immoral, or fatteningAlexander Woollcott

American Writer, 1887 - 1943

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LIPIDS

DEFINITION

Lipids are a family of compounds that include triglycerides (fats and oils), phospholipids (e.g. lecithin), and sterols (e.g. cholesterol)

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LIPIDS

TRIGLYCERIDESAre the chief form of fat in the diet and the major

storage form of fat in the body• Over 90% of the fats we eat are triglycerides• Are composed of three fatty acids attached to

glycerol• Can be simple (where the three fatty acids are the

same) or mixed (where at least one of the fatty acids are different)

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LIPIDS

TRIGLYCERIDES

Glycerol -- An organic alcohol composed of a three carbon chain with a hydroxyl group on each of its three carbons

HydroxylGroup

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LIPIDS

TRIGLYCERIDES

Fatty Acid -- an organic compound composed of a carbon chain with hydrogens attached; has an acid group at one end and a methyl group at the other end

Acid GroupMethylGroup

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LIPIDS

TRIGLYCERIDES

A Mixed Triglyceride

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LIPIDS

FATTY ACIDSDiffer from one another by:• Chain length

– Affects the way the fat is absorbed• Short (less than 6 carbons) and medium (6-10

carbons) chain fatty acids are absorbed directly into the blood

• Long chain fatty acids are made into triglycerides in the intestinal cells, assembled into chylomicrons which are transported through the lymphatic system to the blood

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LIPIDS

FATTY ACIDSDiffer from one another by:• Degree of saturation

– A saturated fatty acid’s chain is filled to capacity with hydrogen

– A monounsaturated fatty acid contains one double bond

– A polyunsaturated fatty acid contains more than one double bond

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LIPIDS

FATTY ACIDSDiffer from one another by:• Degree of saturation

Saturated and unsaturated fatty acids

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LIPIDS

FATTY ACIDS• Whether a fat is soft or hard depends on which

fatty acids are incorporated into it– Fats with shorter fatty acids are softer and melt more

readily• Humans as well as animals can synthesize fatty

acids• Within limits the type of fat eaten will determine

the types of triglycerides made• Saturated fats tend to raise blood cholesterol;

monounsaturated and polyunsaturated fats tend to lower blood cholesterol

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LIPIDS

FATTY ACIDSHydrogenation

Hydrogenation -- a chemical process by which hydrogens are added to unsaturated or polyunsaturated fats to reduce the number of double bonds making them more saturated (solid) and more resistant to oxidation (rancidity)

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LIPIDS

FATTY ACIDSConfiguration

Cis Bonds • Hydrogens on either side of the double

bond on the carbon chain are either both “up” or both “down” such that both are on the same side of the molecule

• Are typical of the configuration in natural foods (except in milk and butter, which contain trans bonds)

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LIPIDS

FATTY ACIDSConfiguration

Trans Bonds • Hydrogens are on opposite sides of the double bond,

that is one “up” and one “down” across from each other• Are not essential• Provide no known health benefit• Their safety is questioned

– Trans fatty acids raise LDL and lower HDL at least to the same extent that saturated fatty acids do

– Trans fatty acids may be carcinogenic– Are now seen to be more damaging than saturated fats

• Will have to be listed on labels by 2005

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LIPIDS

FATTY ACIDSConfiguration

Cis and trans bonds

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LIPIDS

FATTY ACIDSConfiguration

Trans Bonds (continued)• Are more stable than cis bonds • During hydrogenation, some of hydrogen atoms

shift around some double bonds, changing them to trans bonds

• Using oil for frying causes some of the cis bonds to convert to trans bonds -- if the oil is constantly re-used more of the cis bonds are changed to trans until significant numbers of fatty acids with trans bonds build up

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LIPIDSFATTY ACIDS

Configuration

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LIPIDS

FATTY ACIDSSpecial Cases

Omega 3 Fatty Acids • First double bond is three carbons

from the methyl end of the fatty acid• Abundant in plant and fish oils• Deficiencies unlikely but may lead to

neurological and visual problems• Primary representative is Linolenic

Acid• Beneficial in lowering blood

cholesterol and preventing heart disease

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LIPIDS

FATTY ACIDSSpecial Cases

Linolenic Acid • An essential fatty acid with 18 carbons and

three double bonds (humans cannot synthesize)

• Is a polyunsaturated fatty acid

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LIPIDSFATTY ACIDS

Special CasesLinolenic Acid • Abundant in fats and oils (canola, soybean,

walnut, wheat germ, margarine and shortening made from canola and soybean oil), nuts and seeds, and soybeans

Linolenic Acid

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LIPIDS

Dietary Reference Intake Value

Linolenic Acid

AI• Males over 14 -- 1.6 grams• Females over 14 -- 1.1 grams (except pregnant and

lactating)

2002 Data

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LIPIDS

FATTY ACIDSSpecial Cases

Omega 6 Fatty Acids • First double bond is six carbons from the methyl

end of the fatty acid

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LIPIDS

FATTY ACIDSSpecial Cases

Omega 6 Fatty Acids• Abundant in meats and seeds of plants (and the

oils produced by these seeds)• Important in stimulating skin and hair growth,

regulating metabolism, promoting the transport of fatty acids from the liver to the tissues, and maintaining reproductive performance -- also implicating cancer development in some animals

• Primary representative is Linoleic Acid

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LIPIDS

FATTY ACIDSSpecial Cases

Linoleic Acid

• An essential fatty acid with 18 carbons and two

double bonds (humans cannot synthesize)

• Is a polyunsaturated fatty acid

• Common in vegetable oils

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LIPIDS

FATTY ACIDSSpecial Cases

Linoleic Acid

Linoleic Acid

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LIPIDS

Dietary Reference Intake Value

Linoleic Acid

AI• Males 19 - 50 -- 17 grams• Females 19 - 50 -- 12 grams (except pregnant and

lactating• Males over 50 -- 14 grams• Females over 50 -- 11 grams

2002 Data

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LIPIDSComparison of Dietary Fats

O-3

O-3

O-3

O-3

O-3

O-3

O-6Coconut oil

Polyunsaturated fatsMonounsaturated fatsSaturated fats

Animal fats and the tropical oils of coconut and palm are mostly saturated

O-6O-6

Omega-6Omega-6

ButterBeef tallowPalm oilLard

Some vegetable oils, such as olive and canola, are rich in monounsaturated fatty acids

O-6

Many vegetable oils are rich in polyunsaturated fatty acids

Omega-6Safflower oil

Omega-6

Olive oilCanola oilPeanut oil

Omega-3Omega-6

Sunflower oilCorn oilSoybean oilCottonseed oil

Omega-6Omega-6

Omega-6Omega-6 O-3

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LIPIDS

PHOSPHOLIPIDSPhospholipids -- Compounds similar to

triglycerides but with choline (a B-Vitamin) (or similar compound) and a phosphorus containing acid in place of one of the fatty acids

• Most have a backbone of glycerol• Contains nitrogen as well as phosphorus• Together with sterols, make up only 5% of

the lipids in the diet• Are soluble in both water and fat

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LIPIDS

PHOSPHOLIPIDS

• Functions– Are major parts of cell membranes– Act as emulsifying agents (keeps other fats in

solution in the blood and body fluids)

• Can be made by the body -- not essential

• Example -- lecithin (an emulsifier found in egg yolks and soybeans)

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LIPIDS

PHOSPHOLIPIDS

Lecithin

PhosphateGroup

Choline

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LIPIDS

STEROLSSterols -- A compound composed of carbon,

hydrogen, and oxygen atoms arranged in rings like those of cholesterol with any of a variety of side chains attached

• Can be made by the body in the liver -- raw material comes from glucose or saturated fatty acids

• Examples -- Cholesterol, Vitamin D, Testosterone (sex hormone)

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LIPIDS

STEROLS

Cholesterol

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LIPIDS

STEROLSCholesterol

• Is the “most famous” sterol• Performs structural and metabolic functions

in the cells• Made in the liver• After manufacture

– May be made into bile– May be deposited in the body’s cells– May accumulate in the arteries

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LIPIDS

STEROLSCholesterol (continued)

Cholesterol Transport• Cholesterol leaves the liver packaged with other

lipids and protein -- called lipoproteins• Blood carries lipoproteins through all of the

arteries• Tissues can extract the lipids from the lipoproteins• To pass into the cells, lipids must first pass the

artery walls -- some are deposited there

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LIPIDS

Cholesterol in selected foods

0 50 100 150 200 250 300

EggTuna, canned in w ater

Sirloin steak, leanHam, lean

CodChicken breast

Ground beef, leanShrimpButter

Ice creamSw iss cheeseCottage cheeseCheddar cheese

Yogurt, plainYogurt, plain

Milk, 2%Milk

Food

item

Daily Value

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LIPIDS

LIPID TRANSPORTWithin the circulatory system there are four main

types of lipoproteins• Chylomicrons

– Made in the intestines– Are the largest and least dense (with the highest percentage

of protein and lowest percentage of fat) of the lipoproteins– Function -- Transport diet-derived fat lipids (mostly

triglycerides) from the intestine to the rest of the body– Cells all over the body remove lipids from the

chylomicrons as they pass by so they get smaller and smaller

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LIPIDS

LIPID TRANSPORTChylomicrons

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LIPIDS

LIPID TRANSPORT• Very Low Density Lipoproteins (VLDL)

– Similar to Chylomicrons but made by different tissues -- made primarily by the liver cells

– Function -- deliver triglycerides to the body’s cells (composed primarily of triglycerides)

– As they loose triglycerides, the VLDL gather cholesterol from other lipoproteins circulating in the bloodstream and eventually become Low Density Lipoproteins (LDL)

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LIPIDS

LIPID TRANSPORT• Low Density Lipoproteins (LDL)

– Made in the liver as VLDL as cells remove triglycerides from them

– Composed primarily of cholesterol– Function -- deliver cholesterol to the body’s

cells– LDL circulates through the body making their

contents available to all the cells– Special LDL receptors in the liver remove LDL

from circulation

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LIPIDS

LIPID TRANSPORT• High Density Lipoproteins (HDL)

– The type of lipoprotein made by the liver and

small intestine

– Function -- pick up excess cholesterol and

phospholipids from the body’s cells and take it

back to the liver (‘reverse’ cholesterol

transport)

– Composed of protein and lipid

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LIPIDS

LIPID TRANSPORT

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LIPIDS

Composition of the lipoproteins

0%

20%

40%

60%

80%

100%

Chylomicrons VLDL LDL HDL

Triglyceride

Phospholipid

Cholesterol

Protein

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LIPIDS

LIPID TRANSPORT

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LIPIDS

LIPID TRANSPORTOther Routes For Cholesterol

Besides being transported in lipoproteins, it can also be transformed into bile by the liver and stored in the gall bladder

• May then be used to emulsify fat and be re-absorbed

• May be trapped by dietary fiber and be excreted

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LIPIDS

LIPID METABOLISMStoring Fat as Fat

• Most cells depend on the special cells of the adipose tissues to take up and store fat

• Lipoprotein lipase (LPL) extracts triglycerides from passing lipoproteins, hydrolyze them, and and pass the components into the cells’ interiors -- there they are re-assembled into triglycerides

• Adipose cells store fat after meals when a heavy traffic of chylomicrons and VLDL loaded with triglycerides pass by

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LIPIDSLIPID METABOLISM

Using Fat As Energy• When cells demand energy, hormone-sensitive lipase

inside the adipose cells responds by dismantling stored triglycerides and releasing the breakdown products (glycerol and fatty acids) directly into the blood

• In the last steps of breakdown, each fat fragment combines with a fragment from the breakdown of glucose before being completely oxidized to carbon dioxide and water

• The body’s fat stores have virtually unlimited capacity• Fat supplies approximately 60% of the body’s on-going

energy needs during rest -- during exercise, an even greater contribution is made

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LIPIDS

FAT IN FOODS

Functions• Provides flavor and aroma• Vitamins A, D, E, and K are soluble in fat• Provides source of energy (9 Calories per gram)• Provides thermal insulation• Waterproofing external surfaces of both plants and

animals• Protects vital organs (padding)

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LIPIDS

FAT IN FOODS

Reducing dietary fat is widely recommended

• Eliminate fat as a seasoning and in cooking• Cut down on intake of red meat• Remove the fat from high fat foods• Substitute high fat foods with specially

manufactured lower fat versions of those foods• Replace high fat foods with natural low fat

alternatives

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LIPIDS

FAT IN FOODS

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LIPIDS

FAT IN FOODS

Health Effects of Fats• Many diseases are linked to excess body fat or

excessive intakes of dietary fat– Obesity– Diabetes– Hypertension– Atherosclerosis (when the arteries that carry blood to

the heart are blocked)

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LIPIDS

FAT IN FOODSHealth Effects of Fats

• Changes people should make– Limit intake of total fat– Limit saturated fat (mostly solid fats) and

cholesterol(found in animal products)• Guidelines

– Total fat should not exceed 30% of the day’s total energy intake

– Saturated fats should contribute less than 10%– Polyunsaturated fats should not exceed 10%– Monounsaturated fats should contribute the remaining

10% or so– Limit cholesterol to no more than 300mg

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LIPIDS

Dietary Reference Intake Value

Adults over 18 -- AI not determined

Saturated fat and cholesterol• Provide no beneficial role in preventing chronic diseases• Are not required at any level in the diet• Should be kept as low as possible while maintaining a

nutritionally adequate diet

2002 Data

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LIPIDS

FAT IN FOODSSources of Dietary Fat

• Butter, margarine, shortening, oils

• Red Meats

• Avocado, bacon, olives

• Fried foods

• Luncheon and other prepared meats

• Salad dressings

• Milk

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LIPIDSFAT REPLACERS

Evaluated and regulated by the FDACHO Based• Derived from cereals, grains, plants• Is the oldest and largest group of fat replacers• Examples

– Oatrim• Identified as hydrolyzed oat flour on labels• Behaves like shortening• Provides 1 Calorie per gram

– Z-Trim,• Is purified insoluble fiber• Made from seed hulls of oats, soybeans, peas,

and rice or bran from corn or wheat• Provides zero Calories

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LIPIDS

FAT REPLACERSProtein Based• Derived from milk, eggs, whey, or vegetable proteins which are

cooked and blended into uniform microscopic spheres similar to fat particles in foods

• Are perceived as being creamy and slippery, simulating the mouth feel of fats

• Cannot be used for frying but can be used un cooked or baked applications such as cheesecake, pastries, pizza, cheese sauces and cream soups

• Examples -- isolated soy protein, microparticulated protein, and modified whey protein

• Provides 4 Calories per gram -- if fully absorbed

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LIPIDSFAT REPLACERS

Fat Based• Modified Fats

– Are triglycerides that are tailored for specific functional properties by altering the selection and configuration of fatty acids on the glyceride molecule

– Examples• Caprenin• Galatrim• Salatrim

• Synthetic Fats (Olestra)– Also known as sucrose polyester– Made from sucrose and edible vegetable oils– Configuration does not occur in nature

• Replaces the glycerol molecule with sucrose• Attaches 6,7, or 8 fatty acids• With this may fatty acids, digestive enzymes cannot get access to break

off the fatty acid side chains• Intact Olestra molecule is too large to be absorbed, remains undigested,

and adds no fat or Calories to food