Chapter 5 - LIPIDS Triglycerides, Phospholipids, and Sterols.

Chapter 5 - LIPIDS

Triglycerides, Phospholipids,

and Sterols

TYPES OF LIPIDS

1. Triglycerides

2. Phospholipids

3. Sterols

TRIGLYCERIDES Triglycerides – Fats & Oils

1. Predominate form of fat in foods

and major storage form of fat in the body

2. Structure – composed of 3 fatty

acids + glycerol

Fatty Acids Organic acid (chain of carbons with

hydrogens attached) that has an acid group at one end & a methyl group at the other end

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Fatty Acids & Triglycerides glycerol + 3 fatty acids

triglyceride + H2O

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FATTY ACIDS

Fatty Acids – carbon chains, vary in:1. Length – affects

absorption2. Saturation –chemical

structure; affects cooking & storage properties and health

Length of carbon chain

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Stearic acid – 18-carbon, saturated

Simplified structure

FATTY ACIDSSaturation Saturated fatty acid – carbon chains filled with hydrogen atoms (no C=C double bonds)

1. Saturated fat – triglyceride containing 3 saturated fatty acids, such as animal fats (butter, lard) & tropical oils (palm, coconut)

2. Appear solid at room temperature

FATTY ACIDS Unsaturated fatty acid – carbon chains

lack some hydrogens (>1 C=C double bond)1. Monounsaturated fat – triglyceride

containing fatty acids with 1 double bond; i.e. canola & olive oil

2. Polyunsaturated fat- triglycerides containing a high % of fatty acids with >2 double bonds; i.e. corn, safflower, soybean, sunflower oils and fish; 3.

Appear liquid at room temperature

Oleic acid – 18-carbon, monounsaturated

Linoleic acid – 18-carbon, polyunsaturated

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Fatty Acids Location of double bonds

Omega number – refers to the position of the double bond nearest the methyl (CH3) end of the carbon chain

Omega-3 fatty acid Omega-6 fatty acid

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Omega-3 and Omega-6 Fatty Acids Compared

FATTY ACIDS Hydrogenated – addition of hydrogen to unsaturated fat

1. Makes it more “solid” or firm 2. Effects stability and protects against oxidation; more “shelf- stable”

3. Widely used by food industry in margarine, shortening, peanut butter, baked goods & snack food

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Hydrogenation

Hydrogenation Cis vs. trans-fatty acids In nature, most double bonds are cis meaning that the hydrogens

next to the double bonds are on the same side of the carbon chain

When a fat is partially hydrogenated, some of the double bonds change from cis to trans

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Cis- and Trans-Fatty Acids Compared

PHOSPHOLIPIDS

Phospholipids – similar to triglycerides in structure except only 2 fatty acids + cholinePhospholipids in foods: Lecithin, egg yolks, soybeans, wheat germ, peanuts

Lecithin

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Phospholipids

1. Functions: part of cell membranes and acts as an emulsifier (helps keep fats in solution)

2. Not a dietary essential; made by the liver

Phospholipids

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Sterols

Structure consists of carbon rings

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STEROLS Important part of:

1. Sex hormones – testosterone 2. Vitamin D 3. Bile (aids fat digestion) 4. Adrenal hormones - cortisol 5. Cholesterol – in foods and

made by the liver; dietary sources include egg yolks, liver, meats, dairy products

Fat Digestion Hydrolysis

Triglycerides monoglycerides, fatty acids, glycerol

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Fat Digestion

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Fat Digestion Mouth

Melting Lingual lipase

Stomach Churning and mixing Gastric lipase

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Fat Digestion

Small intestine Pancreatic lipases Intestinal lipases

Small intestine CCK

Bile and emulsification

Emulsification of Fat by Bile

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Fat DigestionOverview

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Lipid Transport Lipoproteins – clusters of lipids and

proteins that are used as transport vehicles for fat Chylomicrons VLDL = very-low-density

lipoproteins LDL = low-density lipoproteins HDL = high-density lipoproteins

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Size & Compositions of Lipoproteins

Functions of Fats

In the body, fats provide: 1. Energy – 9 kcals/gm

A. Supplies 60% of body’s energy needs at rest

B. Stored as adipose tissue2. Insulation & protection3. Cell membrane constituents

Functions of Fats In foods, fats:

1. Provide energy (9 kcal/gm)2. Contribute flavor, aroma, and tenderness3. Provide satiety4. Carry fat-soluble vitamins (A,D,E & K)5. Provide a source of essential fatty acids

Fatty Acids Essential fatty acids – 2 polyunsaturated fatty acids that must be provided in diet

1. Linoleic – omega-6 fatty acid and Linolenic – omega-3 fatty acid2. Founds in plant oils, nuts, seeds, whole

grains and fish3. Play a role in normal growth &

development and may prevent heart disease, hypertension, arthritis & cancer

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Health Effects of Fats Excess fat intake contributes to many diseases including:

1. Obesity2. Diabetes3. Cancer4. Heart disease

How? 1. High fat diets = high kcal diets 2. High saturated fat intake raises blood

cholesterol 3. High fat intakes may promote cancer

Health Effects of Lipids

Risks from trans fats

Risks from cholesterol

Risks from saturated fats

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Saturated Fats in the U.S. Diet

Dietary Cholesterol

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Health Effects of Lipids Benefits from monounsaturated fats

and polyunsaturated fats Benefits from omega-6 and omega-

3 fats

1. May reduce blood cholesterol

& help prevent cancer

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Dietary Recommendations

1. Limit total fat intake to <30% of kcals

Example: If 2000 kcal diet, then2000 x .30 = 600 kcals/9 kcals per

gram = 65 gms of protein2. Limit cholesterol to <300 mg/day3. Saturated & polyunsaturated fats

each <10% of kcals

Cutting Fat Cuts Calories and Saturated Fat

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Dietary Recommendations1. Use all fats in moderation *1 tsp fat = 5 gm = 45 kcals2. Beware of “hidden fats” – added to

convenience foods, processed foods, & in cooking 3. Choose lean meats, skinless poultry,

nonfat dairy products; limit meats to <7 oz./day4. Choose fish 2-3 times/week5. Choose monounsaturated fats – canola, olive,

peanut, or sesame oils; avoid hydrogenated oils6. Limit egg yolks to 3-4/week

Heart-Healthy Choices

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Comparing Butter & Margarine Labels Comparing Butter & Margarine Labels

Fat Substitutes Types:

1. Carbohydrate based – i.e. Oatrim & Z-Trim; made from plant fibers

2. Protein based – i.e. Simplesse; made from egg white or milk protein

3. Fat based – i.e. Olestra; made from sucrose & fatty acids; passes through body undigested

Fat Substitutes

B. Do they work?1. Potential health benefits – promote

weight loss and lower blood lipids2. But like sugar substitutes, many people

just eat more instead of replacing fat3. Side effects possible with Olestra4. Use in moderation