Download Ch5LIPIDS

LIPIDS
Vocabulary
Fatty Acid:
Saturated Fatty Acid:
Unsaturated Fatty Acid:
Trans Fatty Acid:
Eicosanoid:
Lipase:
Bile:
Micelle:
Enterocyte:
Lipoprotein:
Chylomicron:
HDL:
LDL:
WHAT ARE THE LIPIDS?
• A broad range of organic compounds that dissolve easily in organic solvents, but range in their
solubility in water
• Hydrophobic –
• Lipophilic –
CLASSES of LIPIDS
SIMPLE LIPIDS
• Fatty Acids
• Triglycerides
• Waxes
COMPOUND LIPIDS
• Phospholipids
DERIVED LIPIDS
• Sterols
FATTY ACIDS
•
•
•
•
Key building blocks for lipids
Chains of carbon atoms with a carboxyl group at one end, and a methyl group at the other
May be “free” or attached to another compound
Determine the characteristics of the fat
CHAIN LENGTH
• Short chain =
• Medium chain =
• Long chain =
• The shorter the carbon chain, the more liquid the fatty acid is
SATURATION
• SATURATED FATTY ACID =If all the carbon atoms in the chain are joined with single bonds,
and the remaining bonds are attached to hydrogen
1
• UNSATURATED FATTY ACID = If adjoining carbons are joined by double bonds
• One double bond = monounsaturated fatty acid
• Two or more double bonds = poly-unsaturated fatty acid
• Long-chain saturated fatty acids stack tightly and form solids at room temperature
• Monounsaturated and polyunsaturated fatty acids don’t stack compactly and are liquid at room
temperature
• Short-chain saturated fatty acids are also liquid at room temperature
TWO TYPES OF BOND FORMATION:
• CIS –
• TRANS –
HYDROGENATION: a chemical process by which hydrogens are added to mono or
polyunsaturated fats to reduce the number of double bonds. Result: fats are more saturated (solid)
and resistant to oxidation (rancidity). Hydrogenation produces trans-fatty acids.
NAMING of FATTY ACIDS
• *count carbons from the methyl (omega) end, 18:0, 18:1 omega-3, etc.
FATTY ACIDS
• Nonessential Fatty Acids – our body can make certain fatty acids so they are not required in the
diet
• Essential Fatty Acids – our bodies cannot make C-C double bonds before the 9th carbon from
the methyl end, so we must get these fatty acids from our diet
• EFAs = omega-6 linoleic acid & omega-3 alpha-linolenic acid
• Omega-3 Fatty Acid – double bond at carbon 3: Alpha-Linolenic Acid (ALA), Eicosapentaenoic
Acid (EPA), Docosahexaenoic Acid (DHA)
• Omega-6 Fatty Acid – double bond at carbon 6: Linoleic Acid, Arachidonic Acid
•
•
•
•
Sources of Omega-3 Fatty Acids
Flaxseed, soybean oil, walnuts, some leafy dark green vegetables (ALA)
Fatty fish: salmon, tuna, and mackerel, fish oils (EPA and DHA)
Sources of Omega-6 Fatty Acids
Seeds, nuts, common vegetable oils: corn, safflower, cottonseed, sunflower seed, peanut
(linoleic acid)
Meat (arachidonic acid)
EICOSANOIDS
• A small percentage of fatty acids become eicosanoids
• They contain 20 or more carbons and are important in the inflammatory process, blood vessel
dilation and constriction, and blood clotting
2
Omega-6s
• Linoleic acid is converted to arachidonic acid and eicosanoids are formed.
• Overall effect: constricting blood vessels, promoting inflammation and blood clotting
Omega-3s
• Alpha-linolenic acid is converted to eicosapentanoic acid (EPA) and docosahexanoic acid
(DHA) and eicosanoids are formed
• Overall effect: dilating blood vessels, discouraging blood clotting, and reducing inflammation
TRIGLYCERIDES
STRUCTURE
• Triglyceride - three fatty acids attached to a glycerol backbone
• Diglyceride – two fatty acids +glycerol
• Monoglyceride – one fatty acid +glycerol
TRIGLYCERIDES
FUNCTIONS
• Major lipid in the body and diet
• Stored fat provides about 60% of the body’s resting energy needs – compactly!
• Insulation and protection
• Carrier of fat-soluble compounds
• Sensory qualities – flavor and texture
Compound Lipids: PHOSPHOLIPIDS
• Contain a glycerol bonded to two fatty acids and a phosphate group
• The phosphate group is hydrophilic while the fatty acid groups are lipophilic
• Because of this structure, phospholipids are ideal emulsifiers, and the perfect structure for cell
membranes
FUNCTIONS
Cell Membranes
Lipid Transport
Emulsifiers
PHOSPHOLIPIDS in FOOD
•
•
•
•
A typical diet contains only about 2 grams per day
Lecithin (phosphatidylcholine) is the major phospholipid and is found in:
Liver, egg yolk, soybeans, peanuts, legumes, spinach, and wheat germ
Usually lost during food processing
DERIVED LIPIDS: Sterols
• Sterols are hydrocarbons with a multiple ring structure
• They are hydrophobic and lipophilic
3
• Contain no fatty acids
• Cholesterol is the best-known sterol, found only in animal products
CHOLESTEROL: Functions
• Major component of cell membranes (especially abundant in nerve and brain tissue)
• Precursor molecule: Example - Vitamin D and estrogen are synthesized from cholesterol
• Important in the synthesis of bile acids
CHOLESTEROL: Synthesis
• The liver manufactures most of the cholesterol in our bodies
• The intestine and all cells contribute a small amount
• Overall, the body produces about 1000 mg per day
DIGESTION
• Mouth
• Stomach
• Small Intestine
ABSORPTION
• Most fat absorption takes place in the duodenum or jejunum – micelles carry monoglycerides
and free fatty acids to the brush border where they diffuse into enterocytes
Bile salts are absorbed in the ileum (enterohepatic circulation)
Once in the enterocytes, monoglycerides and free fatty acids are reformed into triglycerides
The triglycerides, cholesterol, phospholipids, and protein carriers form LIPOPROTEIN
Once these lipoproteins leave the cell, they become CHYLOMICRONS and enter the lymph
system
• MCTs, short-chain fatty acids and glycerol are absorbed directly into bloodstream. They do not
enter the lymph system.
•
•
•
•
• Cholesterol and other sterols are poorly absorbed. Overall, about 50% of dietary cholesterol is
absorbed.
• Dietary fat increases cholesterol absorption
• Fiber (especially soluble fiber) and phytosterols decrease cholesterol absorption
LIPIDS in the BODY
• Chylomicrons:
4
• Low-Density Lipoprotein:
• High-Density Lipoprotein:
HEART DISEASE:
• More than 58 million Americans have at least one form of CVD – stroke, hypertension, or
coronary heart disease
• 1 in 9 women, and 1 in 6 men aged 45-64 years of age have some form of heart disease
• Myocardial Infarction (heart attack) is the leading cause of death in American men and women
ATHEROSCLEROSIS
• A slow, progressive disease that begins in childhood and takes decades to advance.
• Basically, plaque (lipid deposits and other substances) forms in response to injuries on the artery
wall
• Plaque can eventually completely occlude the artery leading to MI
• Injury can be caused by: hypercholesterolemia, oxidized LDL, hypertension, smoking, diabetes,
homocysteine, and diets high in saturated fat
What Are The Lipid Related Risk Factors For CVD?
• High LDL Cholesterol and Low HDL Cholesterol
• A diet high in cholesterol
• A diet high in saturated fat
• A diet high in trans-fatty acids
Other Risk Factors: smoking, diabetes, physical inactivity, obesity, male gender, family history
TRANS FATTY ACIDS:
• Trans fatty acids tend to raise total blood cholesterol levels, but less than more saturated fatty
acids
• Trans fatty acids also tend to raise LDL cholesterol and lower HDL cholesterol
• It is not clear if trans fats that occur naturally have the same effect as those produced by
hydrogenating vegetable oils
• Recently included in the Nutrition Facts panel (Jan. 2006)
IMPORTANT DIETARY FACTORS for CVD
• Homocysteine – high levels of this amino acid may promote atherosclerosis, excessive blood
clotting, or blood vessel rigidity
• Omega-3 Fatty Acids
• Soluble Fiber
• Antioxidants – clean up free-radicals (Vitamin E, Vitamin C, etc)
• Other Phytochemicals – isoflavones and lignans
5