Chapter 5 the lipids
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Chapter 5 The Lipids:. Triglycerides Phospholipids Sterols. Objectives for Chapter 5. Discuss synthesis, structures, classification, function and metabolism of lipids Identify the dietary sources of the different types of lipids Discuss the role of lipoprotein in transport of lipids

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Chapter 5 the lipids

Chapter 5The Lipids:




Objectives for chapter 5
Objectives for Chapter 5

Discuss synthesis, structures, classification, function and metabolism of lipids

Identify the dietary sources of the different types of lipids

Discuss the role of lipoprotein in transport of lipids

Describe the relationship of lipids to chronic diseases

List current dietary recommendations for lipids and how to implement them.


  • Lipids are a class of nutrients that includes:

    • Triglycerides (fats and oils)

    • Phospholipids

    • Sterols.

  • Composed of carbon, hydrogen, and oxygen.

  • Lipids are hydrophobic (insoluble in water)

  • Include fat soluble vitamins (ADEK)

  • Provides 9 kcal per gram


  • TG (fats and oils) – composed of 3 fatty acids attached to a glycerol

    • Fatty acid - is a chain of carbon atoms with hydrogen attached that has an acid group (COOH) at one end and a methyl group (CH3) at the other end

    • Glycerol is an alcohol composed of a three carbon chain

Methyl end

Acid end

Fig. 5-1, p. 140


  • Fats are lipids that are solid at room temperature (70 degrees)

  • Oils are lipids that are liquid at room temperature (70 degrees)

  • TGs are 95% of dietary fats

  • Roles of TGs

    • Energy reserve when stored

    • Insulation

    • Shock protection

    • Use carbohydrate and protein efficiently

  • Fatty acids
    Fatty Acids

    • Fatty acids Fatty acids vary in carbon chain lengths, degree of unsaturation, and number of double bonds.

      • Length of the carbon chain

        • Long-chain fatty acids are found primarily in meat, fish, and vegetable oils.

        • Medium- and short-chain fatty acids are found in dairy products.

      • Degree of Saturation- Saturation affects the physical characteristics of the fat and its storage properties

        • Saturated fatty acids carry the maximum possible number of hydrogen atoms.

    Saturated vs unsaturated
    Saturated vs. Unsaturated

    • Saturated - When most of the fatty acids are saturated it is called a saturated fat.

    Stearic acid, an 18-carbon saturated fatty acid

    Saturated vs unsaturated1
    Saturated vs. Unsaturated

    • Unsaturated – Unsaturated fatty acids are missing at least 2 hydrogen atoms and have at least one double bond. There are 2 types

      • Monounsaturated fatty acid (MUFA)

    Oleic acid, an 18-carbon monounsaturated fatty acid

    Saturated vs unsaturated2
    Saturated vs. Unsaturated

    • Polyunsaturated fatty acids (PUFA)

      • lack four or more hydrogen atoms and have at least two or more double bonds.

      • Linoleic and linolenic acid - Essential Fatty Acids (EFAs)

      • When most of the fatty acids in a lipid are polyunsaturated it is called a polyunsaturated fat.

    Linoleic acid, an 18-carbon polyunsaturated fatty acid

    Saturated vs unsaturated3
    Saturated vs. Unsaturated

    • Locations of the double bonds

      • Omega3 - linolenic acid - the first double bond is located at the third carbon from the methyl side

      • Omega 6 - linoleic acid - the first double bond is located at the sixth carbon from the methyl side

    Linoleic acid, an 18-carbon polyunsaturated fatty acid

    Fatty acids1
    Fatty Acids

    Degree of unsaturation

    • Firmness

      • Saturated fats - solid at room temperature. Mostly from animal sources

      • Polyunsaturated fats - liquid at room temperature. Found in vegetable oil except, cocoa butter, palm oil, palm kernel oil, and coconut oil

    • Stability

      • Saturated fat is more resistant to oxidation.

      • Monounsaturated fat is less susceptible to spoilage.

      • Polyunsaturated fat spoils most readily.

    Essential fatty acids
    Essential Fatty Acids

    Essential Fatty Acids

    • Linoleic Acid - Omega-6 Family and 18 carbon

      • They are PUFA,

      • Can make arachidonic acid—a conditionally essential fatty acid with 20 carbons and 4 double bonds

      • Supplied by vegetable oils and meats

    Essential fatty acids1
    Essential Fatty Acids

    • Linolenic Acid and 18 Omega-3 Family

      • EPA - eicosapentaenoic acid, 20 carbon, 5 double bonds

      • DHA - docosahexaenoic acid, 22 carbons and 6 double bonds

        • important for eyes, brain development, and heart disease.

    • Eicosanoids – omega 3 & 6

      • Made from arachidonic acid and EPA

      • Like hormones but have different effects on different cells

      • Include prostaglandins, thromboxanes, and leukotrienes

    • Essential fatty acid deficiencies are rare in the US but my occur in children fed low fat or fat free diet

    Fatty acids2
    Fatty Acids

    Hydrogenation –

    • Hydrogen atoms are added to monounsaturated or polyunsaturated fats

    • Act more like saturated fats

    • resistant to oxidation

    • Prolong shelf life

    • Becomes solid at room temperature

  • Trans-Fatty Acids vs. Cis

    • Naturally, most double bonds are cis, hydrogen next to the double bonds are on the same side.

    • Trans, hydrogens on opposite side of the carbon.

    • Trans fatty acids behave like saturated fat in the body.

  • Cis- and Trans-Fatty Acids Compared

    Major food sources of trans fat for american adults
    Major Food Sources of Trans Fat for American Adults



    • contain glycerol, 2 FAs and a phosphate group with a choline.

    • A well-known phospholipid is lecithin, made by the liver

      • Food sources of lecithin include eggs, liver, soybeans, wheat germ and peanuts.

    • Soluble in both water and fat

    • Roles of phospholipids

      • Transport lipids and FSV through Plasma membrane

      • Used as emulsifiers in food industry


    • Sterols

      • cholesterol, vit D, testorone

      • Multiple-ring structure.

      • Found in plant and animal foods

      • Cholesterol is found in animal foods only - meat, eggs, fish, poultry and dairy products


    • Roles of sterols

      • Needed to make bile acids, sex hormones, adrenal hormones and vitamin D

      • Component of cell membranes

      • Liver produces 800-1500mg of cholesterol daily

      • Cholesterol forms deposits in the artery wall causing artherosclerosis.

    Fat digestion
    Fat Digestion

    • Mouth –

      • hard fat begin to melt as they reach body temperature

      • salivary glands - lingual lipase digests short and medium chain fatty acids found in milk.

    • Stomach—

      • Lingual lipase breaks down triglycerides to produce diglycerides and fatty acids

      • gastric lipase breaks down a small amount of fat.

      • Little fat digestion takes place in the stomach.

    Fat digestion1
    Fat Digestion

    • Small Intestine –

      • most of the digestion takes place in the small intestine.

      • Cholecystokinin (CCK) signals gallbladder to release bile.

      • Pancreatic and intestinal enzymes breaks lipids to monoglycerides and fatty acids.

      • Phospholipids are broken down as well.

      • Sterols are absorbed intact as is.

      • Bile is reabsorbed in the small intestine

    • Colon or large intestine

      • Soluble fibers traps some bile and excreting it from the body through the large intestine.

    Lipid absorption
    Lipid Absorption

    • Lipid Absorption

      • Glycerol and short and medium-chain fatty acids diffuse and are absorbed directly into the bloodstream.

      • Monoglycerides and long-chain fatty acids form micelles, are absorbed, and are reformed into new triglycerides.

      • With protein they are transported by chylomicrons





    Long-chain fatty acids


    Large lipids such as monoglycerides and long-chain fatty acids combine with bile, forming micelles that are sufficiently water soluble to penetrate the watery solution that bathes the absorptive cells. There the lipid contents of the micelles diffuse into the cells.

    Lipid transport
    Lipid Transport

    • Lipid transport is made possible by a group of vehicles known as lipoproteins. There 4 lipoproteins

      • Chylomicrons

        • Largest of the lipoproteins

        • Least dense

        • Get smaller as triglyceride portion is removed by the cells

      • VLDL (Very-Low-Density Lipoproteins)

        • Composed primarily of triglycerides

        • Made by the liver

        • Transport lipids to the tissues

        • Get smaller and more dense as triglyceride portion is removed

    Lipid transport1
    Lipid Transport

    3. LDL (Low-Density Lipoproteins)

    • Composed primarily of cholesterol

    • Transport lipids to the tissues

      4. HDL (High-Density Lipoproteins)

    • Composed primarily of protein

    • Transport cholesterol from the cells to the liver

    Lipid transport2
    Lipid Transport

    • Health Implications

      • High LDL is associated with higher risk of heart attack and is known as “bad” cholesterol.

      • High HDL seems to have a protective effect and is known as “good” cholesterol

    Storing fat

    Storing Fat as Fat

    Adipose tissue readily stores fat.

    Provides twice the energy as carbohydrate and protein

    1 lb of body fat = 3,500 cal

    Lipoprotein lipase (LPL) breaks triglycerides as they pass, directs the parts into the cells to be used for energy or storage.

    Using Fat for Energy

    Fat supplies 60% of the body’s ongoing energy needs.

    lipase inside the adipose cells hydrolyzes triglycerides when needed for energy.

    Fasting metabolizes fat but needs carbohydrate and protein for complete breakdown.

    Ketone bodies

    Storing Fat

    Health effects of lipids
    Health Effects of Lipids

    • Normal blood lipid profile

      • Total cholesterol  200 mg/dL

      • LDL cholesterol  100 mg/dL

      • HDL cholesterol  60 mg/dL

      • Triglycerides  150 mg/dL

    • Atherosclerosis - Cholesterol accumulates in the arteries

    • saturated fats raise LDL

    • Trans fat increase LDL cholesterol and decrease HDL cholesterol

    • Cholesterol has less effect on blood cholesterol than saturated fat and trans fat.

    Health effects of lipids1
    Health Effects of Lipids

    • Increasing dietary MUFA & PUFA is the most effective way to prevent heart disease.

    • omega-3 fats help to reduce risk of heart disease and stroke

    • Balance omega-6 and omega-3 intakes

    • Cancer - Fat does not initiate cancer development but may be a promoter once cancer has developed

    • Obesity- consequence of high fat diet

    Recommended intakes of fat
    Recommended Intakes of Fat

    • DRI and the 2005 Dietary Guidelines recommends fat at 20-35 % of energy intake.

    • FDA - 10% of energy intake from saturated, 30% of energy intake total fat

    • 2005 Dietary Guidelines - choose a diet low in saturated fat and cholesterol and moderate in total fat.

    Recommended intakes of fats
    Recommended Intakes of Fats

    • Recommended Intakes of Fat

      • Daily Values

        • 65 g fat based on 30% of 2000-kcal diet

        • 20 g saturated fat based on 10% of 2000-kcal diet

        • 300 mg cholesterol

      • USDA Food Guide considers saturated fats discretionary kcalories.

      • Too little fat can be detrimental to health.

    Recommended intakes of fat1
    Recommended Intakes of Fat

    • Linoleic acid AI

      • 5% - 10% of energy intake

    • Linolenic acid AI

      • 0.6 - 1.2% of energy intake

    Reducing fat in your diet
    Reducing Fat In Your Diet

    • Cook with olive oil

    • Nibble on nuts

    • Feast on fatty fish, high in omega 3

      • But beware of mercury

    • Limit Fatty Meats, Milk Products, and Tropical Oils

    • Limit hydrogenated foods

    Reducing fat in your diet1
    Reducing Fat in Your Diet

    • Fat replacers

      • Artificial, ingredients derived from carbohydrate, protein or fat.

      • Replace fat in foods, but no added kcalories

      • Olestra is safe but it deceases absorption of fat-soluble vitamins and may cause diarrhea.

    • Limit Fatty Meats, Milk Products, and Tropical Oils

    • Limit Hydrogenated Foods

    • Adopt the Mediterranean diet

      • Focus on whole grains, potatoes, and pasta, vegetables and legumes, low fat cheeses, yogurt, fruits, fish and seafood, poultry, a few eggs and little meat


    Extra credit 5 points:

    Go to the supermarket and compile a list of 10 foods that contain hydrogenated fat in the ingredient list and document the amount of trans fat listed on the nutrition fact panel