The Lipids: Triglycerides, Phospholipids, and Sterols

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The Lipids Triglycerides, Phospholipids, and
Sterols

• Chapter 5

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Introduction

• Poor health from fat consumption is seen when a
  person consumes either
• Too much fat
• Too little fat
• Too much of some kinds of fat
• Lipids Fat
• Family of lipids
• Triglycerides (TG) (fats oils)
• Phospholipids
• Sterols

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Chemists View of Fatty Acids and Triglycerides

• Lipids
• TG, Phosolipids, and sterols
• Composed of C, H, and O
• Have more C H supply more E per gram
• Most are TG w/ glycerol backbones and three fatty
  acids (f.a.)

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Chemists View of Fatty Acids and Triglycerides

• F.A. vary in C chain lengths, degree of
  unsaturation, and of double bonds (d.b.)
• Trans-fatty acids

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Chemists View of Fatty Acids and Triglycerides

• Preview of lipids
• Triglycerides glycerol and 3 fatty acids
• Fatty acids even number of carbons
• 4-24Cs 18C most common in foods
• Saturated or unsaturated
• Mono or polyunsaturated

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Chemists View of Fatty Acids and Triglycerides

• Fatty acids
• Organic acid
• Methyl group (CH3) at one end acid group (COOH)
  at other
• Usually even number of Cs
• Saturation

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Chemists View of Fatty Acids and Triglycerides

• Unsaturated
• Monounsaturated f.a.
• Lack 2H atoms have 1 d.b.
• When most of the f.a.s are monounsat its called a
  monounsaturated fat
• Polyunsaturated f.a.s (PUFA)
• Lack 4 or more Hs have at least 2 or more d.b.
• When most of the f.a.s are polyunsaturated its
  called a polyunsaturated fat

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Chemists View of Fatty Acids

• Location of d.b.
• Nearest the methyl end of the carbon chain
• Assigned an Omega number
• Omega- 3-polyunsat f.a.
• Linolenic acid are essential f.a.
• Soybean and canola oils, flaxseed, walnuts
• Omega- 6-polyunsat f.a.
• Linoleic acids are essential f.a.
• Vegetable, i.e. sunflower, safflower, corn, and
  soy bean oils
• Monounsaturated fatty acids
• Omega-9 groups
• Oleic acid most predominate in diet
• Olive, canola oils

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Chemists View of Fatty Acids and Triglycerides

• Triglycerides
• Three fatty acids attached to Glycerol backbone
• Formed via series of condensation reactions
• Usually contain mixture of fatty acids

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Chemists View of Fatty Acids and Triglycerides
pg 137
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Chemists View of Fatty Acids and Triglycerides

• Degree of unsaturation
• Firmness
• Polyunsaturated fats
• Saturated fats
• Length of carbon chain
• Stability
• Sat fat is more resistant to oxidation
• monounsat fat is slightly less susceptible to
  spoilage
• Polyunsat fat spoils most readily
• Protection from rancidity

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Chemists View of Fatty Acids and Triglycerides

• Degree of unsaturation
• Hydrogenation
• Trans-fatty acids

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Chemists View of Fatty Acids and Triglycerides
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Chemists View of Fatty Acids and Triglycerides
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Chemists View of Phospholipids and Sterols

• Phospholipids
• Contain glycerol, 2 f.a. and a phosphate group
  with a molecule of choline
• Solubility in fat and water
• Emulsifiers in food industry
• Roles

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Chemists View of Phospholipids and Sterols

• Sterols
• Food sources
• Cholesterol
• Plant sterols
• Roles of sterols
• Starting material for bile acids, sex hormones,
  adrenal hormones, and vit. D
• Structural component of cell membranes
• Liver produces 800-1500mg cholesterol per day
• Atherosclerosis

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Lipid Digestion

• Fats are hydrophobic
• Tend to separate from watery fluids in GI tract
• Digestive enzymes are hydrophilic
• Goal of fat digestion
• Dismantle triglycerides for body to absorb and use

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Lipid Digestion

• Mouth
• Lingual lipase released by salivary glands
• Stomach
• Strong muscle contractions disperse fat into
  smaller droplets
• Fat then exposed to Gastric lipase

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Lipid Digestion

• Small intestine
• Cholecystokinin (CCK)
• Pancreatic and intestinal enzymes
• Phospholipids are hydrolyzed
• Sterols are absorbed
• Bile routes
• Enterohepatic circulation
• Soluble fibers are effective
• in trapping some bile and
• excreting it from the body thru the large
  intestine

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Emulsification of Fat by Bile
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Hydrolysis of a Triglyceride
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Enterohepatic Circulation of Bile
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Lipid Absorption

• Directly into bloodstream
• Glycerol and short- medium-chain fatty acids
  diffuse and are re-absorbed directly into the
  bloodstream
• Lymphatic system
• Larger molecules, Monoglycerides and long-chain
  f.a.s, form micelles that get reabsorbed, and are
  reformed into new triglycerides. With protein
  they are transported by chylomicrons
• When packaged with protein its then transported
  so that cells all over body may select needed
  lipids

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Lipid Transport

• Lipid transport is made possible by a group of
  vehicles known as lipoproteins
• Four main types of lipoproteins
• Chylomicrons
• Very-low-density lipoproteins (VLDL)
• Low-density lipoproteins (LDL)
• High-density lipoproteins (HDL)

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Health implications

• High LDL is associated with higher risk of heart
  attack and is known as a bad cholesterol
• High HDL seems to have a protective effect and is
  known as good cholesterol
• Factors that lower LDL and raise HDL
• Genes influence lipopro activity

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Role of Triglycerides

• Provide the cells with energy
• 9 kcalories per gram
• Adipose tissue
• Virtually unlimited ability to store fat energy
  in body
• Secretes hormones
• Skin insulation, shock absorption, cell
  membranes, and cell signaling pathways

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Essential Fatty Acids

• Linoleic acid Omega-6 fatty acid
• Linolenic acid Omega-3 fatty acid
• EPA DHA-important for eyes, brain, and heart
• Fatty acid deficiencies
• Rare in US and Canada
• Occur in infants and children with fat-free or
  low-fat diets

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A Preview of Lipid Metabolism

• Adipose cells store fat after meals
• Lipoprotein lipase
• Triglycerides reassembled inside adipose cells
• Using fat for energy
• Hormone-sensitive lipase inside the adipose cells
  hydrolyzes TG when needed for E
• During fasting the body metabolizes fat, but
  requires CHO and pro for complete fat breakdown
• Ketone bodies can be made from fat fragments

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Health Effects of Lipids

• Heart disease
• Elevated blood cholesterol
• Saturated fat
• Dietary choices
• Trans-fats
• Dietary cholesterol

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Health Effects of Lipids

• Heart disease
• Monounsaturated fats
• Replace saturated and trans fats
• Reduces blood cholesterol
• Dietary sources
• Omega-3 fats
• Benefits
• Dietary sources
• Omega-6 to omega-3 ratio

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Health Effects of Lipids

• Cancer
• Promotion rather than initiation of cancer
• Dietary fat and cancer risk
• Obesity
• Cutting fat from diet reduces kcalories

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Recommended Intakes of Fat

• DRI and Dietary Guidelines
• Diet low in saturated and trans fat
• Diet low in cholesterol
• 20 to 35 percent of daily energy from fat
• AI set for linoleic and linolenic acids
• Daily Values (DV) on food labels
• Saturated fat and cholesterol
• Risk of insufficient fat intake

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From Guidelines to Groceries

• Very lean and lean options of meat and meat
  alternative products
• Fat-free and low-fat milk products
• Wide variety of vegetables, fruits, and whole
  grains
• Avoid invisible fat from high-fat cheese, baked
  fried goods
• Choose wisely from many available food products

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From Guidelines to Groceries

• Fat replacers
• Ingredients derived from CHO, pro, or fat
• Replace fat in foods
• Artificial fats offer sensory and cooking
  qualities but no kcalories.
• Research on olestra supports its safety but it
  decreases the absorption of fat-soluble vits and
  may cause digestive distress in some
• Read food labels
• Total fat, saturated fat, trans fat, and
  cholesterol
• Compare products
• Daily Value vs. kcalories from fat