2- What foods are good sources of EPA and DHA? Please type your answers now.

Transcription

1 2- What foods are good sources of EPA and DHA? Please type your answers now.

2 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).

3 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.

4 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.

5 Essential Fatty Acids LINOLEIC CH 3 (CH 2 ) 4 CH=CHCH 2 CH=CH(CH 2 ) 7 COOH 18:2 n-6 LINOLENIC CH 3 CH 2 CH=CHCH 2 CH=CHCH 2 CH=CH(CH 2 ) 7 COOH 18:3 n-3 EICOSOPENTAENOIC ACID- (EPA) CH 3 CH 2 CH=CHCH 2 CH=CHCH 2 CH=CHCH 2 CH=CHCH 2 CH=CH(CH 2 ) 3 COOH 20:5 n-3 DOCOSOHEXAENOIC ACID (DHA)

6 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!

7 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

8 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!

9 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)

10 The red balls for the CO2H groups represents the glycerol portion of the triglyceride

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

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15 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!

16 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

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

19 Melting Points of Unsaturated fatty acids are LOWER!

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21 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 H H O C C CH 2 CH 2 CH 2 C CH 2 CH CH 2 CH CH CH 2 CH 2 CH 2 CH 2 CH 3 Palmitoleic acid O

22 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

23 Conclusion Complex lipids contain long-chain carboxylic acids called fatty acids. These fatty acids have 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

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25 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)

26 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.

27 The physical state of of a triacylglycerol at at room temperature provides a clue to to the the degree of of unsaturation in in its its fatty acids. Oils are liquids at room temperature because they contain a large proportion of unsaturated fatty acids. Both fats and oils are insoluble in water. Tristearin (a fat) contains only saturated fatty acids (stearic acid) and would be a solid at room temperature.

28 LEARNING CHECK

29 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?

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

33 You are probably now asking. So what is all the fuss about trans fats?

34 What are Trans Fatty Acids?

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37 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

38 Saturated and Trans Fats: Comparing Butter and Margarine Butter Margarine spread Squeeze margarine Grams of fat in 1 tablespoon Saturated fat Trans fat Other fats SOURCE: Food an Drug Administration

39 Total, Saturated, and Trans Fat Content of Selected Foods Total fat grams per serving Other fats Trans fat Saturated fat 0 French fries Doughnut Pound cake Potato chips Candy bar Milk (whole) SOURCE: Food an Drug Administration

40 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

41 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

42 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.

43 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

44 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

45 Recommended Fat Intake Men Women Adequate daily intake of fat: Linoleic acid 17 grams 12 grams Alpha-linolenic acid 1.6 grams 1.1 grams = about 3 4 teaspoons of vegetable oil Acceptable Macronutrient Distribution Range = 20 35% of total daily calories as fat

46 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).

47 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