Nutrition

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Chapter 6: Lipids

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Properties of Lipids

  • Do not readily dissolve in water

  • Fats are solid at room temperature

  • Oils are liquid at room temperature

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Functions of Lipids

  • Provide energy
  • Satiety
  • Flavor and mouth feel
  • Insulation
  • Protect internal organs
  • Transport fat-soluble vitamins
  • Efficient storage of energy
  • 80% lipid, 20% protein and water

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Triglycerides

  • Triglycerides are the main form of lipids in food and body (storage)

  • Energy dense (9 kcal /g)

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Triglycerides

Glycerol + 3 FA’s Triglyceride + 3 H20

H

H--C--OH

H--C--OH

H--C--OH

H

O

HO-C-R

O

HO-C-R

O

HO-C-R

+

H O

H--C--O--C--

O

H--C--O--C--

O

H--C--O--C--

H

R + H2O

R + H20

R + H20

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Text art 06_02

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Structure

  • Esterification
  • Joining 3 fatty acids to a glycerol unit
  • De-esterification
  • Release of fatty acids-results in free fatty acids
  • Diglyceride
  • Loss of one fatty acid
  • Monoglyceride
  • Loss of two fatty acids

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Structure of Fatty Acids

  • Fatty acids
  • Function is dependent on:
  • Length
  • Degree of saturation
  • Location of double bonds
  • Configuration/Shape

  • Glycerol backbone

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Fatty Acid Chain Length

  • Long chain FA: > 12 Carbons
  • Predominant in food (meats, fish)

  • Medium chain FA: 6 - 10 Carbons
  • Account for ~4-10% of all FA

  • Short chain FA: < 6 Carbons
  • Found in dairy products

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Saturated Fatty Acid

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Monounsaturated Fatty Acid

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Polyunsaturated Fatty Acid

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Location of Double Bonds

  • Omega System
  • Double bond closest to omega (methyl) end
  • Omega: refers to the last carbon (methyl group)
  • Omega 6 vs Omega 3 fatty acids

  • Delta (alpha) System
  • Uses the carboxyl end and indicates location for all double bonds

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Fatty Acid Structure

omega end alpha end

H H H H H H H H H H H H H H H H H O

H-C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C-C-OH

H H H H H H H H H H H H H H H H H

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Fatty Acid Nomenclature

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Configuration/Shape

  • cis versus trans

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Common Fatty Acids

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NAME

STRUCTURE

PROPERTIES

Acetic acid

2:0

Formed from glucose and amino acid degradation

Propionic acid

3:0

Formed from odd-chain fatty acids and branched-chain amino acids

Butyric acid

4:0

Found in cows’ milk and butter

Decanoic acid

10:0

Major fatty acid in milk triglycerides

Palmitic acid

16:0

End product of fatty acid synthesis in most tissues

Stearic acid

18:0

Major fatty acid in gangliosides

Oleic acid

18:1 (∆9)

Lowers plasma LDL when substituted for saturated fatty acids

Linoleic acid

18:2 (∆9,12)

Essential fatty acid and precursor of Arachidonic acid

Linolenic acid

18:3 (∆9,12,15)

Essential fatty acid

Arachidonic acid

20:4 (∆5,8,11,14)

Precursor of most eicosanoids

Saturated Fatty Acids

  • Fatty acids with no double bonds
  • Solid at room temperature
  • Animal fats:
  • Dairy: cheeses, ice cream, whole milk
  • Meat: beef, pork, lamb,
  • Plant/tropical oils (cottonseed, coconut)

  • Stearic, lauric, myristic, palmitic

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Saturated Fatty Acid

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Trans Fatty Acids

  • Essentially a saturated fat

  • Raise LDL
  • Lower HDL

  • Intake has increased dramatically
  • Found in margarine, cookies, potato chips, snack chips, onion rings

  • Current intake is~3% of total kcals

risk for heart disease

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Hydrogenation of Fatty Acids

  • Process used to solidify an oil

  • Addition of hydrogen to an unsaturated fatty acid (eliminating the double bond—making it into a saturated fatty acid)

  • Trans fatty acids are a by product of hydrogenation

  • How can we limit intake of these?

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Figure 06_07

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Trans Fatty Acid

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Food Labels

  • % Daily Value on Nutrition Facts label is sum of trans and saturated fatty acids

  • Quantity of trans fatty acids

  • “Trans fat free” has no more than 0.5 g each of trans or saturated fat

Read the food label and look for hydrogenated or partially hydrogenated oils, or trans fatty acids

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Trans Fatty Acids

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Monounsaturated Fatty Acids

  • One double bond
  • Oleic acid (Omega 9)
  • Olive oil, canola oil, nuts

  • Rate of CHD low in Mediterranean countries where diet is rich in olive oil

  • Diet high in MUFA equivalent to low-fat diet in ↓ LDL-C, but does not ↓ HDL-C

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Monounsaturated Fatty Acid

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Polyunsaturated Fatty Acids

  • 2 or more double bonds

  • Provides essential fatty acids (EFAs)
  • Omega 3
  • Omega 6

  • Properties differ between these EFAs

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Polyunsaturated Fatty Acid

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Figure 06_11

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Essential Fatty Acids

Polyunsaturated fatty acids

Body can only make double bonds after the 9th carbon from the omega end

Needed for

  • immune function
  • vision
  • cell membranes
  • production of hormone-like compounds

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Essential Fatty Acid Needs

  • Adequate Intake
  • Approximately 2-4 Tablespoons daily
  • Deficiency
  • Unlikely
  • Toxicity
  • No upper level set

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Omega-3 Fatty Acids

  • Linolenic acid (α-linolenic acid)

  • Forms eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)

  • Metabolized to form eicosanoids

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Omega-3 Fatty Acids

  • Consumption of large amounts of omega-3 fatty acids decreases the ability of blood to clot

  • May:
  • Prevent stroke and heart attacks caused by clots (thrombosis)
  • Reduce risk of stroke caused by blood clots
  • Help some chronic inflammatory conditions
  • Asthma, rheumatoid arthritis, psoriasis

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Omega-3 Fatty Acids

Recommend intake of ~2 servings of fish/wk

  • Shellfish

  • Cold water/fatty fish (salmon, mackerel, sardines, tuna)

  • Consumption of canola or olive oil vs. other plant oils

  • Flaxseed oil
  • 2 tbsp per day

  • Fish oil capsules
  • 900 mg per day
  • Avoid: if have a history of bleeding
    disorder, on blood thinners

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Omega-6 Fatty Acids

  • Linoleic acid

  • Forms arachidonic acid

  • Metabolized to eicosanoids

  • Found in vegetable oils
  • Corn, sunflower, safflower, soybean oils, nuts, seeds, wheat germ

  • Only need ~ 1 tablespoon a day

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Eicosanoids

  • A group of hormone-like compounds

  • By-pass the blood stream and work in the area of origin

  • Regulators of:
  • Blood pressure
  • Clotting
  • Immune responses
  • Inflammatory responses
  • Stomach secretions

  • Prostaglandins, thromboxanes, leukotrienes, prostacyclins, lipoxins

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Eicosanoids Have Different Effects

  • Omega-3 eicosanoids, DHA, EPA
  • ↓ blood clotting
  • ↓ inflammatory responses
  • Reduce heart attack
  • Excess may cause hemorrhagic stroke

  • Omega-6 eicosanoids; Arachidonic acid
  • ↑blood clotting
  • ↑ inflammatory responses

  • Eicosanoids have different effects on different tissues

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American Heart Association
Recommendations

  • Total fat: <30% of total calories

  • Saturated fat: <10% of total calories

  • Monounsaturated fat: 10% of total calories

  • Polyunsaturated fat: 10% of total calories

  • Cholesterol: <300 mg/day

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Phospholipids

  • Hydrophobic and Hydrophillic Ends

  • Functions
  • Component of cell membranes
  • Eicosanoid synthesis
  • Emulsifier
  • Allows fats/lipids to be dispersed in water
  • Bile acids

  • Sources
  • Synthesized by the body as needed
  • Built on a glycerol backbone
  • At least one fatty acid replaced with phosphorus compound
  • Food: egg yolks (lecithin), wheat germ and peanuts

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Emulsifier

Hydrophilic end (attracts water)

Hydrophobic end (attracts lipid)

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Sterols

  • Multi-ringed structure, most known is cholesterol
  • Functions
  • Bile acids, cell membranes
  • Precursor of steroid hormones, sex hormones, adrenal hormones, Vitamin D
  • Sources
  • Synthesized by the liver
  • Food: animal origin

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Lipid Digestion

  • Mouth
  • Lingual lipase (inactive until reaches stomach)

  • Stomach
  • Gastric lipase (digests primarily SCFAs)
  • Muscular contractions mix fat with digestive enzymes
  • Fats generally remain in stomach 2-4 hours

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Lipid Digestion

  • Small intestine
  • Cholecystokinin (CCK) and Secretin
  • Released due to presence of fat in duodenum

  • CCK stimulates release of
  • Pancreatic lipase
  • Bile (to help emulsify fat)
  • Secretin stimulates release of
  • Bicarbonate
  • Raises pH for activation of lipases

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Bile

  • Composed of bile acids, bile pigments, phospholipids (lecithin)

  • Synthesized from cholesterol in the liver

  • Function is to emulsify fat
  • Allows fat to be suspended in watery digestive juices
  • Large fat globules broken down to smaller ones, surface area for lipase action increases
  • Micelles are formed

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Bile

  • Once used for emulsification, can go through 1 of 2 routes:

  • Reabsorbed in small intestine and recycled
  • Binds to fiber in large intestine and excreted
  • This is how fiber (in particular soluble fiber) helps lower blood cholesterol levels

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Enterohepatic Circulation

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End Products of Lipid Digestion

  • Glycerol
  • Fatty acids
  • Cholesterol
  • Lecithin

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Lipid Absorption

  • Micelles
  • Emulsified fat droplets
  • Absorbed across intestinal mucosal cells by diffusion

  • Distal duodenum, jejunum

  • End products of dietary lipid digestion
  • Repackaged into chylomicrons
  • Released into lymph system

  • Bile salts absorbed in the ileum
  • Returned to liver via portal vein to be reused
  • “Enterohepatic circulation”

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Emulsification

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Lipid Transport

  • Water (blood) and oil (fat) are incompatible
  • Unique system of fat transportation needed for lipids to travel in bloodstream

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Lipid Transport

  • Lipoproteins
  • Transport lipids through bloodstream
  • Composed of:
  • Triglycerides, protein, phospholipids, cholesterol

  • 4 different types
  • Chylomicrons
  • VLDL (Very-low density lipoprotein)
  • LDL (Low density lipoprotein)
  • HDL (High density lipoprotein)

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Lipoprotein

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Chylomicrons

  • Large in size
  • Triglyceride–rich (80-90% TG)
  • Transport dietary (exogenous) fat to cells
  • High blood concentrations following a meal

  • Transported via lymph system, enter bloodstream at thoracic duct

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Chylomicrons

  • Lipoprotein lipase (LPL) breaks down TGs in chylos

  • Fatty acids are absorbed by cells (muscle, adipose, etc.)

  • Chylomicron remnants removed by the liver, broken down, and repackaged into VLDL
  • At this point, fats are considered ENDOGENOUS

  • 2-10 hours to clear from bloodstream

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Dietary Fat Absorption

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Very-Low Density Lipoproteins

  • Triglyceride-rich (55-65%)

  • Transports endogenous fats to cells
  • Lipids synthesized in liver

  • Released from liver into bloodstream

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Very-Low Density Lipoproteins

  • Lipoprotein lipase (LPL) breaks down TGs in VLDL

  • Fatty acids are absorbed by cells (muscle, adipose, etc.)

  • VLDL remnants are removed by liver, broken down, and repackaged into LDL

  • 10-12 hours to clear from bloodstream

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Low Density Lipoproteins

  • Cholesterol-rich (45%)

  • Transports cholesterol synthesized by liver

  • Removed from bloodstream via receptors (or scavenger pathway)
  • Receptors down-regulated with high saturated/trans fatty acid diet

  • 2-3 days to clear from bloodstream

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Low Density Lipoproteins

Optimal <100 mg/dl

Factors that raise LDL

  • High saturated fat diet
  • Diet high in trans fatty acids
  • Low fiber diet
  • Sedentary lifestyle

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High Density Lipoproteins

  • Protein rich (45-50%)
  • Synthesized by liver and intestine
  • Picks up cholesterol from dying cells and other sources
  • Transfer cholesterol to other lipoproteins for transport to liver for excretion
  • HDL can also transfer directly back to the liver

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Benefits of High HDL

  • Removes cholesterol from blood
  • May block oxidation of LDL
  • Reduces risk of heart disease
  • Pre-menopausal women have higher HDL

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High Density Lipoproteins

Desirable >60 mg/dl

Factors that raise HDL

Low saturated fat diet

Replacing saturated fats with Mono - unsaturated fats

Exercise

45 minutes 4 times a week

Losing excess weight, if overweight

Moderate amount of alcohol

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Lipoproteins

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Composition of Lipoproteins

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Metabolism of Lipids

  • Fatty acids, monoglycerides and other lipids taken up by tissue cells

  • Can be used in 1 of 4 ways:
  • Immediate source of energy
  • Energy storage (adipose)
  • Incorporation into cell membranes
  • Used as raw material for synthesis of essential compounds (cholesterol)

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Lipids as an Energy Source

  • Hormone sensitive lipase (HSL)
  • Enzyme found in liver and adipose tissue

  • Key enzyme for lipolysis of stored fat

  • Insulin inhibits HSL (inhibits lipolysis)
  • Glucagon activates HSL (leads to lipolysis)

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Lipids as Stored Energy

  • Unlimited capacity for fat storage

  • Lipoprotein lipase (LPL)
  • Located in adipose and muscle cells
  • Facilitates uptake of FA from blood
  • Excess energy intake
  •  LPL synthesis
  •  fat stored in adipose

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Health Implications of Fat

  • Cardiovascular disease
  • Major cause of morbidity and mortality in US
  • >500,000 people die every year
  • ~1.5 million Americans have a heart attack every year

  • Obesity
  • Fat is a concentrated source of calories
  • Abdominal fat associated with  risk for DM and HTN

  • Cancer
  • High fat diet associated with certain forms of cancer

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Heart Disease

  • Cardiovascular Disease (CVD)
  • Disease of the heart and blood vessels

  • Coronary Heart Disease (CHD)
  • Damage that occurs when blood vessels carrying blood to the heart (the coronary arteries) become narrow and occluded
  • Leading cause of death in US
  • Myocardial infarction (MI)
  • Accounts for ~50% of CVD deaths
  • Major underlying cause is atherosclerosis

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Development of CHD

  • When blood flow via coronary arteries is interrupted

  • Heart attack (myocardial infarction) may result leading to
  • Irreversible damage to heart muscle
  • Irregular heart beat or stopped heartbeat
  • 25% of people do not survive their 1st MI

  • Cerebrovascular accident (CVA) or stroke
  • When blood flow to part of brain is interrupted causing part of brain to die

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Myocardial Infarction (MI)

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Signs of a Heart Attack

  • Intense, prolonged chest pain
  • Shortness of breath
  • Sweating
  • Nausea and vomiting
  • Dizziness
  • Weakness
  • Jaw, neck, shoulder pain
  • Irregular heartbeat

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Risk Factors for Heart Disease

Modifiable

  • Smoking
  • Hyperlipidemia
  • Total Chol >200 mg/dL
  • Low HDL-C <35 mg/dL
  • Hight LDL-C
  • Obesity
  • HTN
  • Physical Inactivity
  • Diabetes Mellitus

Non-Modifiable

  • Age
  • Male >45
  • Female >55
  • Male gender
  • Family history of CHD

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Other Risk Factors

  • Serum Homocysteine
  • Amino acid
  • High level in blood associated with increased risk of MI
  • Causes damage to blood vessel wall

  • Reduce blood level by:
  • Increasing folate, B6 and B12 intake
  • Fruits, vegetables, etc.

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Other Risk Factors

  • C-Reactive Protein (CRP)
  • Acute phase protein that increases during systemic inflammation
  • Levels in blood increase during inflammation
  • Biochemical marker for CVD

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National Heart Lung and Blood Institute, Adult Treatment Panel III Guidelines for CHD (2001)

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Reduce Your Risk
(Primary Prevention)

  • ↓ dietary saturated fat, trans fatty acid, and cholesterol
  • ↑ MUFA and PUFA to recommended amounts
  • ↑ dietary fiber
  • Maintain healthy weight
  • Don’t smoke
  • Alcohol in moderation
  • Folate intake
  • Low glycemic index load

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Secondary Prevention
(After a Heart Attack)

  • Primary prevention techniques
  • Medication
  • Megadoses of vitamin E (400-800 IU/day)

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Therapeutic Lifestyle Changes

  • Total Fat 25-35% of total kcals
  • SFA <7% of total kcals
  • MUFA Up to 20% “ “
  • PUFA Up to 10% “ “
  • CHO 50-60% of “ “
  • Protein 10-20% of “ “
  • Cholesterol <200 mg/d
  • Fiber 20-30 g/d

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Therapeutic Lifestyle Changes

  • Other recommendations:
  • Plant stanols/sterols
  • 2 g/d
  • Kcals
  • To maintain optimal weight, prevent weight gain
  • Physical activity
  • Expend at least 200 kcal/d

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Medical Therapy

  • Statin drugs
  • Lipitor, Zocor, Mevacor, etc.
  • Successful in reducing blood cholesterol

  • Benecol and Take Control
  • Plant stanol ester
  • Cholesterol-lowering effect
  • Compete with cholesterol in the micelle and reduce absorption of dietary cholesterol

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Medical Therapy

  • Surgical Intervention
  • Angioplasty
  • Coronary Artery Bypass Graft (CABG)

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Angioplasty

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Stent placement

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CABG surgery

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NAME STRUCTURE PROPERTIES

Acetic acid 2:0 Formed from glucose and amino acid degradation

Propionic acid 3:0 Formed from odd-chain fatty acids and branched-

chain amino acids

Butyric acid 4:0 Found in cows’ milk and butter

Decanoic acid 10:0 Major fatty acid in milk triglycerides

Palmitic acid 16:0 End product of fatty acid synthesis in most tissues

Stearic acid 18:0 Major fatty acid in gangliosides

Oleic acid 18:1 (∆9) Lowers plasma LDL when substituted for

saturated fatty acids

Linoleic acid 18:2 (∆9,12) Essential fatty acid and precursor of Arachidonic

acid

Linolenic acid 18:3 (∆9,12,15) Essential fatty acid

Arachidonic acid 20:4 (∆5,8,11,14) Precursor of most eicosanoids

LDL Cholesterol

<100 Optimal

100-129 Near optimal

130-159 Borderline high

160-189 High

>190 Very high

Total Cholesterol

<200 Desirable

200-239 Borderline high

>240 High

HDL Cholesterol

<40 Low

>60 High