Chapter 5 The Lipids:

1
Chapter 5The Lipids

• Triglycerides
• Phospholipids
• Sterols

2
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.

3
Lipids

• 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

4
Triglycerides

• 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

5

Methyl end
Acid end
Fig. 5-1, p. 140
6
TG
7
Triglycerides

• 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

8
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.

9
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
10
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
11
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
12
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
13
Omega-3 and Omega-6 Fatty Acids Compared
14
Saturated and Unsaturated Fatty Acids Help Shape
Foods
15
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.

16
(No Transcript)
17
Essential Fatty Acids

• Essential Fatty Acids
• Linoleic Acid - Omega-6 Family and 18 carbon
• They are PUFA,
• Can make arachidonic acida conditionally
  essential fatty acid with 20 carbons and 4 double
  bonds
• Supplied by vegetable oils and meats

18
(No Transcript)
19
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

20
Essential Fatty Acids
21
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.

22
Cis- and Trans-Fatty Acids Compared
23
Major Food Sources of Trans Fat for American
Adults
24
Phospholipids

• Phospholipids
• 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

25
Phospholipids
26
Sterols

• 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

27
Sterols
28
Sterols

• 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.

29
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.

30
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.

31
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

32

Monoglyceride
Micelle
Protein
Triglyceride
Long-chain fatty acids
Chylomicron
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.
33
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

34
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

35
Chylomicrons One Type of Lipoprotein
36
The Various Types of Lipoproteins and Their
Composition
37
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

38
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 bodys 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

39
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.

40
Atherosclerosis
41
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

42
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.

43
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.

44
Recommended Intakes of Fat

• Linoleic acid AI
• 5 - 10 of energy intake
• Linolenic acid AI
• 0.6 - 1.2 of energy intake

45
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

46
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

47
Homework

• 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