Transcript BIOL 103 Ch 6 Lipids for Students SS15

Lipids: Not Just Fat
BIOL 103, Chapter 6
Today’s Topics
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What are Lipids?
Fatty Acids are Key Building Blocks
Triglycerides
Phospholipids
Sterols
Lipids Digestion and Absorption
Lipids in the Body
Lipids in the Diet
Lipids and Health
Lipids
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Essential nutrients
Provide energy
Help transport fat-soluble nutrients
Contribute to flavor and texture of food
What are Lipids?
• Lipids include…
– Triglycerides (most abundant lipids)
• In body: stored in adipose tissue
• In food: “fats and oils”
– Phospholipids (~2% of dietary lipids)
• Plant and animal origin
• Body can make them
• Soluble in fat and water
– Sterols (very, very small % of lipids)
• Most well known: Cholesterol
Fatty Acids are Key Building Blocks
• Fatty Acids
– Determine whether a fat is solid or liquid at room
temperature
– Basic structure: (-COOH); (-CH3)
• Chain length
– 2-24 Carbon length
Fatty Acids are Key Building Blocks
• Saturation
– Saturated fatty acids
• All single bonds between carbons
– Unsaturated fatty acids
• One or more carbon bonds is a double bond
1. Monounsaturated fatty acid (MUFA)
2. Polyunsaturated fatty acid (PUFA)
– Fats with more double bonds are generally more
liquidy
Saturated vs. Unsaturated Fatty Acids
Fatty Acids are Key Building Blocks
Cis fatty acids
• Occurs naturally
• Chain is bent
Trans fatty acids
• Produced by hydrogenation
(adds hydrogen to an
unsaturated fatty acids)
• A small portion of trans fat
can occur naturally
• Chain is straighter
Trans Fat
• In health, trans fatty acids are known to raise
LDL (“bad”) cholesterol, and lower HDL (“good
cholesterol”), promote systemic inflammation,
and increase triglycerides in your blood.
• History and how it is made:
– In Europe (1910)
– In US (1960s)
Fatty Acids are Key Building Blocks
• Nonessential and essential fatty acids
1. Nonessential fatty acids
• Can be made in the body
• Not “essential” to have in your diet
Fatty Acids are Key Building Blocks
• Nonessential and
essential fatty acids
(cont.)
2. Essential fatty acids
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Can’t be made in the
body
Must come from food
Omega-3 (alphalinolenic acid) and
omega 6 (linoleic acid)
Used to make
eicosanoids
Triglycerides
• Structure
– Glycerol + 3 Fatty Acids
• Functions
1. Energy source: 9 kcal/g
2. Energy reserve: form of stored energy in adipose
tissue (“fatty tissue”)
3. Insulation and protection:
1. Visceral fat (fat around organs)
2. Subcutaneous fat (fat under skin to protect/insulate body)
4. Carrier of fat-soluble nutrients
5. Sensory qualities in food
Apple vs. Pear
Triglycerides in Food
• Found in a variety of fats and oils
• Classified by their most prevalent type
– Saturated fatty acids: animal foods and tropical
oils
– Polyunsaturated fatty acids: plant or animal based
• Omega-3: soybean, flaxseed oils; salmon, tuna
• Omega-6: seeds, nuts, corn oil, meat, poultry, eggs
What are the positive and negative
consequences of hydrogenating a fat?
(Problem Set 6, #3)
• Oxidation causes food to spoil and damage body tissues
Pros
Cons
Phospholipids
• Structure
– Glycerol + 2 fatty acids + phosphate
group
• Functions:
1. Emulsifiers
• Keep fat suspended in water
• Keep oil and water mixed
2. Structural element for cell
membranes
Phospholipids
• Cell membrane
– Double layer of
phospholipids
– Store fatty acids
temporarily and
release them as
needed  can
regulate them
closely
– Important role in
nerve cells
• e.g. Ach
Phospholipids
• Lipid transport
– Stomach
• Breaks fat into tiny particles for digestion (i.e. lingual
lipase)
– Intestine
• Continues emulsifying fat (i.e. bile)
– Blood
• Coat the surface of the lipoproteins that carry lipid
particles to their destinations in the body
Phospholipids
• Emulsifiers (Lecithin)
– In body
• Phospholipid with
choline 
phosphotidylcholine
– In food
• Blend of phospholipids
with different nitrogencontaining components
• Used as emulsifiers
(e.g. salad dressing,
chili, sloppy-joe mixes,
and chewing gum).
Phospholipids
• Phospholipids in food
– Occur naturally in plants and animals
– Examples: Egg yolks, liver, soybeans, peanuts
– Not dietary essential because the body can make
it
Sterols
• A category of lipids that
include cholesterol
• Structural
characteristics:
– Multiple ring structure
– Contain no fatty acids
Sterols
• Cholesterol functions:
1. Structural component of cell membranes
2. Precursor to other substances
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Examples: Vitamin D, Sterol Hormones, Manufacture
bile salts
• Cholesterol synthesis in liver
• Sterols in food
– Found only in animal foods
Lipid Digestion
• Digestion of triglycerides (TG), cholesterol,
and phospholipids (PL)
– Mouth
• Chewing + lingual lipase
– Stomach
• 30% Triglycerides + gastric lipase  FFA and DG
Lipid Digestion (cont.)
• Small Intestine
– Emulsified by bile
– Rest of the “exposed” TG and DG are digested by
pancreatic lipase
– Phospholipids digested by pancreatic
phospholipase
– Cholesterol ester digested by cholesterol esterase
– Bile salts surround digested fat and form micelles
Lipid Absorption
Lipid Digestion (cont.)
• Micelles carry digested fat through the watery
environment to microvilli/small intestine
– The lipid components are then absorbed into the
intestinal cells at the microvilli
– Bile salts return to the liver to be used again
• Short-chain FA and glycerol are directly
absorbed into your intestinal cells without the
help of micelles.
Lipids Absorption
• To travel in the bloodstream, lipids are
packaged into lipoprotein carriers
• How?
– In your intestinal cell: MG + FFA rejoin  TG
• Cholesterol esters and phospholipids form here also
– Then, TG, PL, cholesterol esters join protein carrier
 lipoprotein.
– Lipoprotein leaves the intestinal cell 
chylomicron  goes to lymph system 
bloodstream.
Lipid Digestion and Absorption
(Figure 6.21)
Chylomicron Transport
• In the blood stream, chylomicrons are large, fatty
lipoproteins (90% fat)  circulate in the body
while releasing TG
• When reaching capillaries, lipoprotein lipase
“attacks” chylomicrons to remove TG  FFA and
glycerol:
– FFA enter adipose cells  reassembled into TG
– OR FFA enter muscle cells  used for energy
– Glycerol  liver or kidney
• Your liver picks up “left-over” chylomicron and uses them
to build VLDL
Lipids in the Body
1. Very-low-density lipoproteins (VLDL):
– Deliver triglycerides to cells
2. Intermediate-density lipoproteins (IDL)
– Returns to liver and is converted to LDL
3. Low-density lipoproteins (LDL)
– Deliver cholesterol to cells, which body uses to
synthesize membranes, hormones, etc.
– Returns to liver afterwards
4. High-density lipoproteins (HDL)
– Pick up cholesterol for removal or recycling
Lipoprotein Pathway Summary
Lipoprotein density
• Lipoproteins differ by size, density, and
composition of their lipid cores
– In general, larger the lipoprotein, the less dense it
is.
– Size: HDL < LDL < IDL < VLDL < Chylomicron
Problem Set 6, Q#4:
• Describe the differences between LDL and
HDL and protein composition
Lipids in the Diet
• Recommended intake:
– Reduce saturated fat and trans fat
– Total fat: 20-35% of calories
– Less than 10% of calories from saturated fat
Lipids in the Diet
• Essential FA requirements
– Linoleic acid/omega-6 FA should provide about 2%
of calories
– Requirements for omega-3 FA is less well-known
• Omega-6 and omega-3 FA balance
– Ratio of 6:1 (omega-6 to omega-3 FA)
– While omega-3 FA is good for you, consuming too
much of the omega-3 FA can suppress immune
function and prolong bleeding time
Lipids and Health
• Following are examples are diseases associated to high
intakes of saturated and trans fat.
1. Obesity
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Determined by excessive accumulation of body fat leading to a
body weight in relation to height that is significantly greater
than some accepted standard.
High-fat diets promote weight gain
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2. Heart Disease/Cardiovascular Disease
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Leading cause of death in US (1 death/minute)
Major risk factors
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High blood cholesterol (High LDL, low HDL)
Smoking
High blood pressure
Lipids and Health
3. Atherosclerosis
– Slow, progressive hardening and narrowing of
arteries
– Promoted by high blood cholesterol
4. Inflammation and atherosclerosis
– How?
– Smoking, infection, or high blood pressure can
speed up this process described above
Atherosclerosis
AHA diet and lifestyle
recommendations:
• Reducing heart disease risk (pg. 222-226)
– Go over on your own
1. Consume an overall healthy diet
2. Aim for a healthy body weight
3. Aim for a desirable lipid profile
4. Aim for normal blood pressure
5. Aim for normal blood glucose levels
6. Be physically active
7. Avoid use of and exposure to tobacco products
AHA diet and lifestyle
recommendations (cont.):
• Reducing heart disease risk (pg. 222-226)
8. Balance calorie intake and physical activity to
achieve or maintain a healthy body weight
9. Consume a diet rich in fruits and vegetables
10. Choose whole-grain, high fiber foods
11. Consume fish, especially oily fish, at least
2/week
12. Limit your intake of saturated and trans fat
AHA diet and lifestyle
recommendations (cont.):
• Reducing heart disease risk (pg. 222-226)
13. Minimize your intake of beverage foods with
added sugars
14. Choose and prepare foods with little or no salt
15. If you consume alcohol, do so in moderation
16. Follow the AHA recommendations when eating
outside of the home
Metabolic Syndrome
• ¼ US adults has metabolic syndrome
• Has at least 3 of the following symptoms:
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Excess abdominal fat
High blood glucose
High serum triglycerides
High blood pressure
Low HDL cholesterol
Putting it all together
• Healthy People 2020 objectives target:
1. Reducing deaths from heart disease and stroke
2. Reducing the number of adults with high blood
cholesterol levels
Cancer
• Stages of development:
– Initiation: a mutation in cell’s genetics 
abnormal cell
– Promotion: when a chemical (e.g. carcinogen)
encourages initiated cells to become active
• Reversible stage
– Progression: when promoted cells multiply and
invade healthy tissues
Cancer (cont.)
• Dietary and lifestyle factors for reducing
cancer risk:
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Maintain a healthful weight
Adopt a physically active lifestyle
Consume a healthy diet
If you drink alcohol, limit consumption