2- What foods are good sources of EPA and DHA?

• Please type your answers now.

• Foods that are good sources of EPA and DHA include fish such as salmon, albacore tuna, sardines, lake trout, and mackerel.

• (Some texts give the following mnemonic for remembering the recommended fish as SMASH: Salmon, Mackerel, Anchovies, Sardines, and Herring.)

• All of these fish contain high levels of the two omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

• The reason for this dietary recommendation was research that supported the idea that omega-3 fatty acids reduce the risk of cardiovascular disease by decreasing blood clot formation, blood triglyceride levels, and growth of atherosclerotic plaque…….

• with consequent improvement of arterial health and decrease in blood pressure and the risk of sudden death and heart arrythmias.

• We can understand why this should be so since it is known that EPA is a precursor for the synthesis of prostacyclin, which inhibits clumping of platelets and thus reduces clot formation.

• Note also that DHA is one of the major fatty acids in the phospholipids of sperm and brain cells, as well as in the retina.

• It has also been shown to reduce triglyceride levels by an as yet understood mechanism.

• Note also that linolenic acid is an essential fatty acid which seems to reduce the incidence of cardiovascular disease

• However, it is not clear whether it acts alone or because it is the precursor of DHA and EPA.

Essential Fatty AcidsLINOLEIC CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH

18:2 n-6

LINOLENIC CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH

18:3 n-3

EICOSOPENTAENOIC ACID- (EPA)

CH3CH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)3COOH

20:5 n-3

DOCOSOHEXAENOIC ACID – (DHA)

• 3- What do you predict the physical state would be of a triglyceride with three unsaturated fatty acid tails?  Explain your reasoning.

• Please type your answers now.

• REMEMBER! Think structure & bonding!

• The physical state of a triglyceride with three unsaturated fatty acid tails would be an OIL!

• Complex lipids that contain mainly unsaturated fatty acids are liquids (oils) at room temperature.

• But why? • Let us develop this a bit

NOTE WELL!!• Structure is a function of BONDING!• Bonding influences the STRUCTURE

STABILITY, SHAPE & CHARGE of molecules!• Bonding therefore influences the CHEMICAL

AND PHYSICAL BEHAVIOR of molecules.• Bonding affects the interaction of molecules.• BONDING IS EVERYTHING!

Structure• Stearic acid: a typical saturated fatty acid

with 18 carbons in the chain

• Oleic acid: a typical unsaturated fatty acid with 18 carbons in the chain (double bonds tend to be at C9 counting from COOH end)

• The red balls for the CO2H groups represents the

glycerol portion of the triglyceride

Note the kink as a result of the double bond in the unsaturated fatty acid

Saturated fatty acids- Molecular structure• Saturated fatty acids have all single bonds and

have a maximized number of hydrogens attached to the carbons

• Saturated fatty acids are linear and inflexible, because they are more tightly stacked!

Unsaturated fatty acids Molecular structure

• Unsaturated fatty acids usually have more than one double bond.

• A double bond introduces a kink in the molecular structure of unsaturated fatty acids.

• Kinks - prevent stacking – lend flexibility

Note melting point, number of carbon atoms (chain length) and number of kinks (double bonds)

Melting Points of Unsaturated fatty acids are LOWER!

• An unsaturated fatty acid has one or more carbon-carbon double bonds in the chain

• The first double bond is usually at the ninth carbon

• The double bonds are not conjugated and are usually cis

• cis double bonds result in a bent chain and lower melting point

CO

OCH2CH2

C CCH2

CH2

CH2

CH2

CH2

CH2

HH

CH2

CH2

CH2

CH2CH3

Palmitoleic acid

This table clearly indicates the decrease in melting point with increased unsaturation of the fatty acid

• The notation 14:0 means 14 carbons and 0 double bonds in the molecule (saturated). The notation 18:2 means 18 carbons in the molecule and 2 double bonds

Conclusion• Complex lipids contain long-chain carboxylic acids called

fatty acids. These fatty acids have 10-24 carbon atoms in the carbon chain.

• Saturated fatty acids contain no carbon-carbon double or triple bonds, and thus saturated fats pack tightly. (A disadvantage of this is that tightly packed, saturated fats clog arteries as atherosclerosis).

• Unsaturated fatty acids contain one (monounsaturated) or more double bonds (polyunsaturated).

• Because of these double bonds, polyunsaturated fats do not pack well – its like building a wall with bricks vs. irregular-shaped objects

• Remember! Polyunsaturated fats have more than one double bond. This leads to kinks.

• Kinks - prevent stacking and lend flexibility

Fatty Acid Properties• Melting point of fatty acids increases with increasing carbon

number (i.e increasing size)• Melting point of a saturated fatty acid is higher than an

unsaturated fatty acid with the same number of carbons• Typical saturated fatty acids are tightly packed together• cis double bonds prevent good alignment of molecules in

unsaturated fatty acids leading to poor packing• Double bonds lower melting point relative to saturated acid.• Melting point of unsaturated fatty acid are lower than that

of a saturated fatty acid of the same carbon number (size)

• As in the case for saturated fatty acids, the melting points of unsaturated fatty acids increase with increasing hydrocarbon chain length.

• The melting points of unsaturated fatty acids are lower than those of the corresponding saturated fatty acid with the same number of carbon atoms.

• Also, as the number of double bonds in the chain increases, the melting points decrease.

• The melting point of a saturated fatty acid is greater than that of an unsaturated fatty acid of the same chain length, because saturated fatty acid chains tend to be fully extended and to stack in a regular structure, thereby causing increased intermolecular attraction.

• Introduction of a cis double bond into the hydrocarbon chain produces a rigid 30 degree bend.

• Such “kinked” molecules cannot stack in an organized arrangement and thus have lower intermolecular attractions and lower melting points.

The physical state of a triacylglycerol at room temperature provides a clue to the degree of unsaturation in its fatty acids.

The physical state of a triacylglycerol at room temperature provides a clue to the degree of unsaturation in its fatty acids.

Tristearin (a fat) contains only saturated fatty acids (stearic acid) and would be a solid at

room temperature.

Oils are liquids at room temperature because they contain a large proportion of unsaturated fatty acids. Both fats and oils are insoluble in water.

LEARNING CHECK

• Now you can see why there is such a big fuss about DEEP SEA FISH OILS in the diet!

• So what’s the fuss about good fats and bad fats?

• What’s the fuss about saturated fats and unsaturated fats in our diets?

Its best to use fats with low melting points! i.e Unsaturated fats.

• You are probably now asking…….• “So what is all the fuss about trans fats?”

What are Trans Fatty Acids?

• Trans fatty acids are formed when vegetable oil is hydrogenated (for solidification).

• Trans fatty acids are – found in:

• fried foods, • commercial baked goods (donuts, cookies,

crackers), • processed foods, • margarines

Saturated and Trans Fats: Comparing Butter and Margarine

0 5 10 15Grams of fat in 1

tablespoon

Squeezemargarine

Margarinespread

Butter

Saturated fatTrans fatOther fats

SOURCE: Food an Drug Administration

Total, Saturated, and Trans Fat Content of Selected Foods

05

1015202530

Total

fat g

rams p

er se

rving

Frenchfries

Doughnut Pound cake Potatochips

Candy bar Milk(whole)

Other fatsTrans fatSaturated fat

SOURCE: Food an Drug Administration

• When plants and animals build fatty acids they make the cis forms. BUT

• Food manufacturers found that foods like chips with the trans form have a longer “shelf life”

• Natural cis fatty acids tend to turn rancid and spoil

• However, although natural cis fatty acids turn rancid and spoil, it is the cis form is used by the body.

• The process of hydrogenation, in which hydrogens are added to unsaturated fats, produces a mixture of saturated fatty acids and standard and trans forms of unsaturated fatty acids

• Trans fatty acids have an atypical shape that affects their chemical activity

• Consequently, when the trans form is eaten in foods the body tries to use it for the same functions BUT whereas the cis form is flexible, the trans forms are not flexible which causes them to adhere to surfaces

• As a result the trans form can raise LDL levels (BAD Ch) and lower HDL levels ("good cholesterol").

• Therefore……partially hydrogenated (partially hardened) oils in foods should be avoided – because they contain high levels of trans fatty acids.

Fats and Health

• Fats also affect triglyceride levels, inflammation, heart rhythm, blood pressure, and cancer risk

• Best choices = monounsaturated fats and polyunsaturated omega-3 fats

• Limit intake of saturated and trans fats

Fats and Health• Fats affect blood cholesterol levels

– Low-density lipoprotein (LDL) = “bad” cholesterol– High-density lipoprotein (HDL) = “good” cholesterol– Saturated and trans fats raise levels of LDL; trans

fats also lower levels of HDL– Unsaturated fats lower levels of LDL

Recommended Fat Intake

• Adequate daily intake of fat:

= about 3–4 teaspoons of vegetable oil• Acceptable Macronutrient Distribution Range

= 20–35% of total daily calories as fat

Men Women

Linoleic acid 17 grams 12 grams

Alpha-linolenic acid 1.6 grams 1.1 grams

Fats should comprise no more than 30% of the caloric intake.

1 Saturated fats should make up less than 10% of caloric intake.

2.The essential fatty acids (EFAs) are linoleic acid (9,1 2-octadecadienoic acid, an (0-6 fatty acid) and linolenic acid (9,12,1 5-octadecatrienoic acid, an (0-3 fattyacid).

Tips for Reducing Dietary Fats

• Use non-fat or low-fat dairy products and other products

• Use low-fat cooking methods– Bake, roast, steam, broil, stir fry, microwave

• Seldom have fried foods• Choose lean cuts of meat, trim fat