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