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Ch. 6 Fats & other Lipids

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lipids
-hydrophobic
-they lack polar bonds & are not charged
-they don't mix with water
-less dense than water
-ex. fats, steroids, waxes
Lipids 3 categories: foods & human body
1. triglycerides
2. phospholipids
3. sterols
lipids include:
1. fatty acids (bldg block of triglycerides
2. triglycerides
3. phospholipids
4. cholesterols
fatty acids
-contain a hydrocarbon chain & hydrogen atoms with a methyl group at one end & an acid group at the other
short chains fatty acids
2-4 carbons
medium chain fatty acids
6-12 carbons
long chain fatty acids
14-24 carbons
saturated
each carbon atom w/in the chain holds 2 hydrogen atoms. only SB
unsaturated
one or more carbon atoms within the chain lack 2 hydrogen atoms, resulting in at least 1 DB
saturated fatty acids in foods: where found, attributes & examples
-most animal fats have a high proportion of saturated fatty acids
-solid at room temp b/c straight saturated hydrocarbon tail can stack well
-ex. butter, lard
unsaturated fatty acids in food: where found, attributes & examples
-most plant oils tend to be low in saturated fatty acids, high in unsaturated fatty acids
-liquid at room temp b/c kinked unsaturated hydrocarbon tail cannot stack well
-ex. corn oil, olive oil
essential polyunsaturated fats (2)
1. Linoleic acid
- omega-6 fatty acid • End-most DB is 6 carbons from the end of the carbon chain
2. Linolenic acid
- omega-3 fatty acid
• End-most double bond DB is 3 carbons from the end of the carbon chain
ex. cold water fish (salmon)
prostaglandins
• essential FA are precursors of prostaglandins
- Hormone-like substances formed from EPA, DHA, and arachidonic acid
• Effects of prostaglandins:
- Stimulate uterine contractions
- Regulate blood pressure
- Promote immune system response
trans fats definition
Unsaturated fats with at least 1 trans double bond rather than the more common cis double bond
trans fats: form & how produced
less common in nature
• Produced by hydrogenation
Unhealthy for you
-straight chain & DB, acting like a saturated fat & worse
cis form
more common in nature Healthy for you
hydrogenation
- Process that adds hydrogen atoms to liquid vegetable oils
- makes it saturated
partial hydrogenation
- Not all double bonds are hydrogenated.
- Natural cis double bonds convert to the unhealthy trans form.
trans fat & health
Used in many processed foods
- High amounts of trans fats in diet increase heart disease risk by raising blood cholesterol levels.
- FDA requires amount of trans fat displayed on Nutrition Facts panel.
triglycerides: composed of & percentage in food & body
- Composed of 3 fatty acids attached to a glycerol "backbone"
• ~95% of lipids in the body and foods is in the form of triglycerides.
phospholipid: composed of, where found & main function
- Chemically similar to a triglyceride, 1 fatty acid is replaced by a compound containing phosphorus and nitrogen groups
- Lecithin- main phospholipid in foods, such as egg
yolks, liver, wheat germ, peanut butter, and soy
- Phospholipids form a bilayer in water
• The bulk of all cell's plasma or cell membrane is a phospholipid bilayer with embedded proteins
Phospholipids: emulsifiers
- Phospholipids act as emulsifiers, because they have hydrophobic and hydrophilic regions. need for digestion b/c enzymes can get to fat when emulsified
- Hydrophobic region
• Attracts lipids and avoids water
- Hydrophilic region
• Attracts water and avoids lipids
steroids & sterols: general form & examples
- Have skeletons of four fused carbon rings.
• Cholesterol, testosterone, estrogen
steroids: general form & examples
• Steroids are very different from fats in structure and function
- The carbon skeleton is bent to form four fused rings - Example: sex hormones
sterols: general form & examples
- Large molecules consisting of interconnected rings of carbon atoms with side chains of carbon, hydrogen, and oxygen attached
-Cholesterol
• is found in all animal cell membranes
• is nonessential
• forms plaques that cause atherosclerosis
- Cholesterol serves as the raw material for
•Bile
• vitamin D
• Steroid hormones including the sex hormones
cholesterol: description, where found, functions & uses
1. Cholesterol is a sterol, a compound that is more complex than most other lipids.
• is found in all animal cell membranes
• is nonessential
• forms plaques that cause atherosclerosis
2. Cholesterol serves as the raw material for
•Bile
• vitamin D
• Steroid hormones including the sex hormones
Waxes
- Long-chain fatty acid bonds with a long-chain alcohol - "like a triglyceride on steroids"
• High melting point
• Waterproof
• Resistent to digestion & degradation
bile
- made in the liver and stored in the GB
- Bile contains bile salts that aid in lipid digestion.
- Without bile, lipids clump together in large fat globules.
- bile emulsifies fat
what happens to lipids in your body?
In the duodenum, pancreatic lipase digests triglycerides, forming primarily:
- Monoglycerides - Free fatty acids (other final products = glycerol, cholesterol, phospholipid fragments)
Lipid digestion & absorption steps-small intestine (5)
1. large fat droplets enter sm. intestine after meals
2. bile salts emulsify fats into smaller particles
3. lipase (from pancreas) breaks down fat into FA & monoglycerides
4. monoglycerides & FA are absorbed thru villi & then re-form triglcerides
5. triglycerides combine with cholesterol, protein & phospholipids to form chylomicrons
Overall Lipid digestion & absorption steps (5)
1. Stomach — minor fat digestion occurs
2. Liver — produces bile that helps emulsify fat
3. Pancreas — secretes lipase into small intestine
4. Small intestine — main site for lipid digestion & absorption. once absorbed, long-chain FA are packaged for transport thru the lymph & bloodstream.
5. Anus — less than 5% of undigested fat is excreted in feces
lipoproteins
-water-soluble structures that transport lipids thru the bloodstream.
-The just-eaten fat travels in the bloodstream as CHYLOMICRONS.
- Body tissues can extract whatever fat they need from chylomicrons.
- The remnants are then picked up by the liver, which dismantles them and reuses their parts.
Very-low-density lipoproteins (VLDL)
- carry triglycerides and other lipids made in the liver to the body cells for their use.
• VLDL primarily carries triglycerides. if in the liver will increase cholesterol
- High levels may contribute to atherosclerosis
Low-density lipoproteins (LDL)
- transport cholesterol and other lipids to the tissues. LDL are made from VLDL after they have donated many of their triglycerides to body cells.
- LDL commonly called "bad" cholesterol
• Conveys cholesterol TO the tissues/cells
• May become oxidized (sticky) LDL and contribute to atherosclerotic plaque
- larger, lighter, and richer in cholesterol. Deliver cholesterol and triglycerides from the liver to the tissues.
- LDL - Less healthy
High-density lipoproteins (HDL)
-are critical in the process of carrying cholesterol for disposal.
HDL commonly called "good " cholesterol
• Transports cholesterol from tissues and to the liver (to make bile) where it can be eliminated. away from plaque build up
- smaller, denser, and packaged with more protein. HDL scavenge excess cholesterol and phospholipids from the tissues for disposal.
- HDL = Healthy
recycling bile salts
Enterohepatic Circulation
- After bile salts are used to aid lipid digestion, the salts are absorbed in the ileum and return to liver for the production of new bile.
- Soluble fibers and plant sterols/stanols interfere with bile and cholesterol absorption. (good thing not returned to liver, so liver must use cholesterol to make new bile salts)
Note: Some synthetic margarine spreads contain plant sterols or stanols.
usefulness of fats in the body (5)
1. - chief storage form of Energy. provides most energy for body's work.
• the C-H covalent bond stores much energy - just as in the hydrocarbons of gasoline
• 9 Calories per gram
2. -Cushion of internal organs
3. -Insulation in the skin, thanks to internal fat in the skin
4. adipose tissues = secretes hormones, stores fat
5. part of cell membranes
using triglycerides for energy
• Adipose cells can break down triglycerides into fatty acid and glycerol molecules before releasing them into blood stream.
• Liver can convert glycerol to glucose, another energy source.
• Triglycerides provide 9 kcal/g (carbohydrate & protein provide 4 kcal/g) a lot of energy from a little bit of fat
How Can I Use My Stored Fat For Energy?
- When low on fuel, the body draws on its stored fat for energy.
- Fat cells respond to the call for energy by dismantling stored fat molecules and releasing fat components into the bloodstream.
- Upon receiving these components, cells break them down further into fragments. Each fragment is combined with a fragment derived from glucose, and the energy-releasing process continues, liberating energy, carbon dioxide, and water.
- Without glucose (carbs), fat is incompletely broken down to ketones
Lipids acceptable range & US dietary guidelines
20-35%
U.S. Dietary Guidelines 2005
- 20 to 35% of total calories
- < 10% of calories from saturated fats
- < 300 mg cholesterol daily
- Avoid foods with trans fatty acids
Lipids & Health: Cardiovascular disease (CVD)
CVD: diseases of the heart and blood vessels
Most common forms of CVD are:
• Heart disease ("coronary artery disease")
• Stroke
1 in 3 adult Americans have some form of CVD. - -
-Responsible for ~ 36 % of deaths in the U.S.
artherosclerosis: what is it & what can result
— disease in which lipid- containing plaques build up inside arteries
Plaque forms in an artery when something irritates the lining of the artery wall.
• Plaque narrows arteries, interfering with circulation. • Plaque may also result in the formation of a fixed clot— a thrombus.
embolus formation
A thrombus (blood clot) that breaks away and travels through the blood is an embolus.
- If an embolus lodges in the heart, it can cause a heart attack (myocardial infarction).
- If an embolus lodges in the brain and deprives brain cells of oxygen and nutrients, a stroke results.
arteriosclerosis
- Condition that results from atherosclerosis -
- Characterized by loss of arterial flexibility/stiff
- Commonly referred to as "hardening of the arteries"
- Contributes to hypertension
hypertension
- Chronic condition characterized by abnormally high BP levels
- May cause hardened arteries to tear or burst
genetics & CVD
• Genetics (family history) cannot be modified.
- Genes may:
• code for physical conditions that increase risk hypertension and diabetes.
• influence way circulatory and immune systems respond to diet.
• Some day genetic testing may be available to determine markers for CVD.
Modifiable risk factors
• Smoking
• Hypertension*
• Diabetes*
• Excess body fat*
• Elevated blood cholesterol (LDL)* • Physical inactivity
*Influenced by diet
lipoproteins & atherosclerosis
- Transport lipids in the blood
- Play major role in atherosclerosis development
- Carry different types of lipids and can influence plaque formation differently
lipoprotein profile
Blood test that determines total cholesterol, HDL & LDL cholesterol, and triglyceride levels
desirable levels of lipoproteins
• Total Cholesterol < 200
• LDL Cholesterol < 100
• HDL Cholesterol 40-60
• Triglycerides < 150
* 40-60 for men, 50-60 for women
High-sensitivity C-reactive protein (hs-CRP)
•Protein produced primarily by liver in response to infection and inflammation
•Marker for CVD and hypertension
- marker for inflammation (including arteries)
Note: A "marker" is an early physiological warning sign that can be measured.
Coronary calcium: definition & causes
-consists of specks of calcium (tiny calcifications) in arteries of the heart.
-Associated with: smoking, excess body fat, high blood pressure, LDL cholesterol.
reduce risk of atherosclerosis: dietary (SF, TF, Cholesterol, monounsaturated, polyunsaturated)
• Impact of dietary fat & cholesterol on blood lipids:
- Saturated fats increase LDL and HDL - Trans fats increase LDL but lower HDL - Cholesterol increases LDL
-Monounsaturated fats lower LDL but not HDL
- Polyunsaturated fats lower LDL and lower HDL in some people.
dietary recommendations: Limits on fats
Limit:
- Saturated fats to <7% of total kcal
- Trans fats to <1% of total kcal
- Total fat to 35% or less of total kcal
-Choose unsaturated fats (esp. monounsaturated) to replace saturated and trans fats.
Omega-3 FA: sources, action & results
Sources: Fatty fish, canola oil, walnuts, and flaxseed
Actions: Reduces inflammation, blood clotting, and blood pressure
May reduce risk of heart disease
Omega-6 FA: sources, action & results
• Sources: Animal fats and vegetable oils
• Actions: Increases inflammation and blood clotting
• May also reduce risk of heart disease
food selection & preparation: reduce dietary fat (7)
Strategies to reduce dietary fat include:
- Reduce intake of fried foods
- Purchase lean cuts of meat and trim visible fat.
- Replace some fatty foods with reduced-fat or fat-free alternatives.
- Replace high-fat sandwich meats with nut butter
- Choose low-fat snack foods.
- Use less salad dressing on salads.
- any oil heated to high temp changes to "trans"
fat replacers/substitutes
Saturated fat replacers were developed to meet consumer requests for lower fat foods.
- Oatrim, Simplesse & Olean
other dietary modifications (5)
• Increase soluble fiber intake (helps eliminate bile so liver has to make more cholesterol)
• Reduce intake of refined carbohydrates
• Monitor alcohol intake
- A small amount can raise HDL but increase blood triglyceride levels and blood pressure
• Lose excess body fat
• Follow the Mediterranean Diet Pyramid
what if lifestyle changes don't work
People who cannot lower blood cholesterol levels after lifestyle modifications may need prescription drugs such as:
Statins — class of medications that interfere with liver's metabolism of cholesterol
"Zetia©" — inhibits intestinal absorption of cholesterol
ethanol
- Simple 2-carbon compound
- Formed from the fermentation by yeast of glucose
- In beer, wine, vodka, whiskey, sake, koumiss, and kefir
alcohol production
Alcohol production requires: • Microbes (e.g., yeast)
• Warm conditions
• A source of simple sugar
Typical sugar sources for common beverages are grains, fruits, and potatoes.
• Koumis is made from mare's milk. • Kefir is from camel's milk.
how body process alcohol
• Alcohol requires no digestion.
- Rapidly absorbed in the mouth, esophagus, stomach, and small intestine
•Detoxification: begins in stomach where alcohol dehydrogenase metabolizes ~20% of alcohol consumed.
- Most alcohol is absorbed in small intestine.
- Travels to the liver where it is metabolized.
main source of fat
processed vegetable oil in fast & commercially prepared foods
Main pathway for alcohol metabolism (2)
1. At low doses, enzymes convert alcohol to acetaldehyde and then to acetyl CoA.
2. Acetyl CoA can be metabolized to provide energy or used to form fatty acids.
2nd pathway for alcohol metabolism
1. At high doses, the liver's ability to metabolize alcohol using the dehydrogenase pathway is overwhelmed.
- Under these conditions, the microsomal ethanol oxidizing system (MEOS) is used.
- MEOS wastes energy as the heat produced dissipates into the environment.
factors that influence alcohol metabolism (2)
1. Gender
- Men have more gastric alcohol dehydrogenase
- men have larger livers that can metabolize more alcohol at a time
2. Prior drinking history
- Regular drinkers develop tolerance.
- Level of alcohol-detoxifying liver enzymes increase.
- As tolerance increases, alcohol dependence (alcoholism) is likely to occur.
classifying drinkers (6)
abstainer = none or fewer than 12 drinks/year
light = 1-13 drinks/month
moderate = 4-14 drinks/week
heavy = 3 or more drinks a day
binge (male) - 5 or more drinks/occasion
binge (female) = 4 or more drinks/occasion
alcohol abuse & dependence
• People who abuse alcohol drink to the extent that it harms their mental and physical health as well as their relationships.
• About 17% of men and 8% of women become dependent on alcohol at some point in their lives.
alcohol abuse (3)
Drinker:
- has control over alcohol intake
- does not have a powerful craving for alcohol
- does not experience withdrawal symptoms
alcohol dependence (3)
Drinker:
- has uncontrollable need to drink
- is unable to limit alcohol consumption
- suffers withdrawal symptoms and develops tolerance
alcohol and health
Effects vary from person to person due to:
- Differences in overall health/brain shrinks
- Drinking habits
- Genetic backgrounds
Alcohol affects every cell in the body, and excesses can do damage to every organ system
alcohol & GI tract (3)
-Alcohol irritates lining of the GI tract.
-Contributes to ulcers of the esophagus and stomach.
-Chronic alcohol contributes to alcohol pancreatitis
alcohol & the brain (3)
-Effects on the CNS appear within a few minutes after consumption.
-Acts as a depressant, slowing transmission of messages between nerve cells.
-Effects on the brain vary and depend on blood alcohol concentration (BAC)
alcohol & the liver (4)
-Excessive amounts of alcohol are converted to fatty acids in the liver (acetyl CoA).
-Fatty liver - condition is reversible, if the person avoids alcohol.
-Continued alcohol consumption results in fat buildup in liver
• destroys liver cells and results in scar tissue
-Liver cirrhosis - irreversible hardening of the liver
alcohol & cardiovascular system & cancer
1. Cardiovascular system
-Excess consumption can damage heart muscle and elevate blood pressure.
2. Cancer
-Chronic drinkers are more likely to develop cancers of oral cavity, esophagus, stomach, liver, pancreas, and colon/rectum.
alcohol & drug interactions (2)
• Prescription and over-the-counter medications may amplify effects of alcohol.
• Alcohol may interact with certain drugs, causing serious side effects.
effect of alcohol & nutritional status
• Moderate alcohol stimulates appetite.
• Excessive alcohol:
- inhibits appetite
- decrease intake of nutrient-dense foods
-interferes w/body's utilization of certain vitamins, minerals & fat
alcohol & body water
• Alcohol is not a "thirst quencher."
• It is a diuretic that suppresses the production of antidiuretic hormone (ADH).
- As a result, kidneys excrete more urine, which is mostly water, and certain minerals and vitamins.
- more water than normal leaves the body
fetal alcohol syndrome (2)
-Alcohol is toxic to cells, including embryonic cells.
-Infants born with fetal alcohol syndrome have physical deformities and experience developmental delays.
health benefits of alcohol (2)
1. Light to moderate alcohol intakes
- Raise HDL cholesterol
- Reduce blood levels of fibrinogen
Decrease platelet stickiness (blood thinner)
2. Controversy over the health benefits of alcohol
- Benefits of drinking red wine and beer rather than white wine and liquor
• Alcohol itself or the antioxidants and certain vitamins in beer and red wines may provide health benefits.
alcohol & physical performance
• American College of Sports Medicine recommendations:
- Athletes should learn about alcohol's effects on health.
- Avoid excessive alcohol during the 48 hrs before an event.
- After exercise, avoid alcohol until body is rehydrated