Why can’t we just avoid lipids?
• Phospholipids and cholesterol are found in our cell membranes.
• We have steroid based hormones.
• We use lipids as other structual units.
• You must take in some lipids.
• 2 to 4 tablespoons of vegetable oil a day, supplemented with an oily fish twice a week is enough.
• Are all oils created equal?
• If I/you avoid cholesterol, saturated fat and trans-fat can you safely eat more?
What is a lipid?
• A lipid is a compound made up of mostly carbon and hydrogen.
• Since they lack oxygen, they are non polar. Thus, they don’t dissolve in water.
Fat vs oil
• A fat is a solid at room temperature.
• A fat generally has few double bonds.
• An oil is a liquid at room temperature.
• An oil will have at least 1 double bond.
Types of lipids
• Our bodies use 3 types of lipids.
• Triglycerides (a)
• Phospholipids (b)
• Sterols (Cholesterol) (c)
Fatty Acid Structure
omega end alpha end
degree of saturation
• A triglyceride is a glycerol molecule bonded to 3 fatty acids.
Saturated vs unsaturated
• The fatty acid that bonds to the glycerol molecule can be saturated or unsaturated.
• A saturated fat has no carbon-carbon double bonds. Thus it is saturated with hydrogen.
Saturated Fatty Acid Structure
omega end alpha end
degree of saturation: single carbon bond
• Contains 1 (mono-unsaturated) or more than 1 (poly-unsaturated) double bonds
• Canola and olive oil tend to have a high % of mono-saturated fats.
• Therefore, they are considered better for you.
Monounsaturated Fatty Acid Structure
omega end alpha end
One double bond
• Have multiple double bonds on each chain.
• They are found in corn, soybean, sunflower and safflower oils.
Polyunsaturated Fatty Acid Structure
omega end alpha end
> 2 double bonds
Omega # fatty acids
• The location of the double bond is important.
• It is counted from the Omega
Essential Fatty Acids
• Omega-3 fatty acid (alpha-linolenic acid)
• Omega-6 fatty acid (linoleic acid)
• Body can only make double bonds after the 9th carbon from the omega end
• Immune function, vision, cell membrane, and production of hormone-like compounds
• The double bond is between the 9th and 10th
• Oleic acid is the major essential Omega 9 fatty acid.
• The double bond is 6 carbons from the omega end (between C6 and C7)
Kinky fatty acids
• In nature, the double bond is always in the cis formation.
• That causes the fatty acid chain to bend
• This bend is called a kink.
• Are similar to triglycerides.
• However, they have only 2 fatty acids bonded to the glycerol molecule.
• A phosphate group takes up the third bonding location.
• This makes the head polar (water soluble).
Functions of Phospholipids
• Component of cell membrane
• Bile acids
• Improves food products
• Found in wheat germ, peanuts, yolks, soy beans, organ meat
• Any lipid that uses cholesterol as its base. Multi-ringed structure
• Do not have a glycerol backbone
• Cholesterol is a sterol
• Waxy substance
• Found in animal foods
Functions of Cholesterol
• Essential component of cell membrane
• Produced by the liver
• Found only in animal products
• Forms important hormones
• Estrogen, testosterone, vitamin D
• Precursor to bile acids
Many hormones are sterols.
So what are trans fats
• Trans fat is short for trans-polyunsaturated fat.
• They are made by the hydrogenation of unsaturated vegetable oil.
• They tend to have a longer shelf life, and a higher melting point than “normal” polyunsaturated fats.
• Regular unsaturated fats are cis fatty acids.
• This causes the “kink” in them.
• Trans fats physically resemble saturated fatty acids.
• However, our bodies have trouble processing them.
• Last longer
• Solids work better in baked goods.
Hydrogenation of Fatty Acids
• Process used to solidify an oil
• Addition of H to C=C double bonds
• Increases shelf life
• Formation of trans fatty acid
• (similar to shape of saturated fatty acid)
Cis and Trans Fatty Acid
Why not just make a saturated fat?
• Trans fats are only partially hydrogenated. If they were fully hydrogenated, it would be too brittle.
Excessive Trans Fatty Acid Intake
• Raises LDL (low density lipoproteins)
• Lowers HDL (High density lipoprotein)
• Increases risk for cardiovascular disease
• Current intake is 3%-4% of total kcal
• On Food Labels Today
• Bodies don’t recognizes trans form so our cells have trouble taking it in.
• Bodies recognize it as a saturated fat which is why it raises LDL
The problem with trans fats
• The double bonds are more likely to interact between chains.
• They won’t go bad, but there is a chance what it forms will be cacogenic.
Typical Sources of Trans Fat
Minimize Intake of Trans Fat
• Limit use of hydrogenated fats
• Limit deep-fried foods
• Limit high-fat baked goods
• Limit use of non-dairy creamers
• Decomposed oils
• Breakdown of the C=C bonds by UV light, &/or O2
• Unpleasant odor and flavor
• PUFA more susceptible
• Limited shelf life
Prevention of Rancidity
• Addition of vitamin E
• Addition of Butylated hydroxyanisol (BHA) and Butylated hydroxytolune (BHT)
lipids in food
• The lipids in food is not just one type. Each food source has a combination of many different fatty acids. That gives each food a
different taste and smell.
Fats and oils in foods
• Lipids are less dense than carbohydrates.
• Therefore, lipids give 9 kCal per gram instead of 4.
Lipid dense food
• Give the majority of their Calories as lipids.
• Salad oil, butter, margarine, and mayonnaise.
• Can be only 30 % fat by weight as opposed to 80.
• However, when used, they can change the texture/volume of the finished product.
Our typical diet
• Lots of lipid rich food.
• Bologna, avocados (guacamole) bacon have 80 % of their Calories from lipids.
• Cheese and peanut butter 75 %.
• Steak and burgers 60 %
• Chocolate, ice cream, doughnuts and whole milk 50 %
• Eggs and lean cuts of meat 35 %
• In Belgium and the Netherlands, they dip French fries in Mayonnaise
• That is not hidden fat.
• Other foods use fat in production.
• Fried food is fried in oil.
• Often, this is a trans-fat since trans-fats have longer lives.
• The food absorbs the fat from the oil.
• Are fried in fat.
• Often Trans-fat
• Therefore, you are getting calories from both fat and the sugar (not to mention the margarine in the dough).
Other questions to ask
• Does it contain whole milk? If yes, it contains a large amount of fats.
• Therefore, cheese and ice cream are lipid dense foods.
Is margarine used in production?
• If yes, the food has a lot of fat (often trans).
• Cookies, cakes, brownies and other baked goods often are high in fat.
• North Americans get most of their lipids from animal fat which is mostly saturated fat (40-60 %).
• Plant oils are mostly (73-94 %) unsaturated fatty acids.
• Canola and olive oil are good sources of mono-unsaturated fats.
• Wheat germ, peanuts, egg yokes, and organ meats are rich in phospolipids
• Lecithin (from egg yokes) is added to salad dressing to keep it mixed.
• Found in animal products only.
• Therefore, all vegetable oils are naturaly cholesterol free.
Therefore, for your next meal
• What will you consider when choosing what you will eat?
• What should you do if you had pizza or fries for lunch?
What about these dishes
• Beijing duck?
• Rotisserie chicken (with skin on)
• Baked turkey (with skin on)
• The skin of birds (especially duck) is rich in lipids.
• Low fat = less than 3 grams (27 Cal) per serving.
• Fat-free = less than 1.5 g of fat per serving (13.5 Cal)
• Reduced fat = less than 25 % fat than normal.
Reduced fat products
• Now have anywhere from 0 to 75 % of original fat content.
• However, those calories have been replaced by carbohydrates.
• Diet margarine
• Starch derivative that binds with water
• Fiber cellulose
• Maltrin, Stellar, Oatrim
• Protein globules
• Olestra or Olean (links fatty acid to sucrose)
• Not digested
• FDA approved for fried snack foods
• Fat-soluble vitamins issue
Digestion of fats
Digestion of Fat in the Stomach
• Gastric lipase
• Activated by an acidic environment
• Acts on triglycerides containing short- & medium-chain fatty acids
Digestion of Fat in the Small Intestine
• Primary site of fat digestion
• Hormone Cholecystokinin (CCK)
• Stimulates release of pancreatic lipase
• Bile acid released
• Emulsifies digested fat
• Fat is broken down
• To monoglycerides and fatty acids
Digestion of Phospholipids
• Enzymes released from the pancreas and cells of the small intestine.
• Phospolipids are broken down to Glycerol Fatty acids and phosphates
Digestion of Cholesterol
• Enzymes released from the pancreas
• Cholesterol is absorbed by the small intestine
Absorption of Fat
• 95% of dietary fat is absorbed
• Diffused into the absorptive cells
• Short- and medium-chain (<12 C) fatty acids
• Are water soluble
• Enter the portal system
• Long-chain fatty acids re-form into triglycerides
• Not water soluble
• Enter the lymphatic system
Carrying Fat in the Bloodstream
• Water (blood) and oil (fat) are incompatible
• Unique system of fat transportation is needed
Transportation of Absorbed Fatty Acids
• Re-formed into triglycerides
• Packaged into chylomicrons
• Lipoprotein lipase
• Breaks down triglycerides in the chylomicrons
• Chylomicron remnant
• Delivered to the liver
Composition and Roles of Lipoproteins
Transportation of Synthesized Fat
• Made primarily by the liver
• Very-Low-Density Lipoprotein (VLDL)
• Low-Density Lipoprotein (LDL)
• High-Density Lipoprotein (HDL)
High-Density Lipoprotein (HDL)
• Synthesized by liver and intestine
• High proportion of protein
• Picks up cholesterol from dying cells and other sources
• Transfers cholesterol to other lipoproteins
• Transfers cholesterol directly back to the liver
Benefits of (a high) HDL (level)
• Removes cholesterol from the bloodstream
• HDL blocks oxidation of LDL
• Reduces risk of cardiovascular disease
• Pre-menopausal women have higher HDL
• Scavenger WBC removes (oxidized) LDL from circulation
• Build-up of plaque on walls of the blood vessels
• Development of atherosclerosis
• Vessel damage caused by:
• Smoking, diabetes, hypertension, homocysteine, high LDL, infection
• Reduces oxidation
• Slows LDL uptake by scavenger cells
Functions of Essential Fatty Acids
Essential Fatty Acid- Omega-3 (alpha-linolenic acid)
omega end alpha end
1st double bond is located on the 3rd carbon from the omega end
Omega-3 Fatty Acid
• Primarily from fish oil
• Also found in canola, walnuts, flax seeds, mussels, crab, shrimp, and soybean oil
• Recommended intake of ~2 servings of fish per week
Essential Fatty Acid- Omega-6 (alpha-linoleic acid)
omega end alpha end
1st double bond is located on the 6th carbon from the omega end
Omega-6 Fatty Acid
• Found in vegetable oils
• Only need ~ 2-4 tablespoons a day
Essential Fatty Acids
• Archidonic acid (Omega-6 )
• Increases blood clotting
• Increases inflammatory responses
• DHA, EPA (Omega-3)
• Decrease blood clotting
• Reduce heart attack
• Decrease inflammation
• Excess may cause hemorrhagic stroke
• Other possible uses: Lower triglycerides, rheumatoid arthritis, behavioral disorders
Signs and Symptoms of Essential Fatty Acids Deficiency
• Flaky, itchy skin
• Retarded growth and wound healing
Functions of Fatty Acids
• Provide energy
• Efficient storage of energy
• Transport fat-soluble vitamins
• Some satiety
• Flavor and mouth feel
• The brain gets the majority of the carbohydrates that you eat. That is because it cannot use fatty acids for energy.
• Other tissues can and do use fatty acids as an energy source.
• A key to dieting is to get the bodily tissue to use the fatty acids instead of the carbohydrates.
A long walk vs a quick run
• The run will burn glucose and glycogen. It will not tap into the fatty acids.
• Going for a long (hour +) walk will cause your body to start to break down fatty acids.
• Adipose cells (A type of connective tissue) store lipids for later use.
Fat vs Carbs for storage
• Carbs are water soluble. When we store them, we store a great deal of water.
• Carbohydrates are denser than fats
• Yield only 4 kCal/g
• Fats are not water soluble. We don’t retain water when we store them.
• Fats are not very dense (less weight)
• Fats yield 9 kCal/ gram
Insulation and protection
• Cushions important organs
• Provides insulation from cold.
• The camel actually uses fat in its humps to insulate from heat.
Fat soluble vitamins
• A,D and K are not water soluble.
• This poses a transportation problem.
• Fats aid in the absorption of these vitamins.
• In our cell membranes, keeps 2 separate environments
• Others allow for mixing of fats with intra/extra cellular fluid.
Function of Cholesterol
• Keeps our cell membranes ridged.
• Base for steroid hormones and bile salts.
• Also in the active form of Vitamin D
• An Emulsifier helps a lipid mix with water.
• Eggs are added to cake batter since they include lecithin, an emulsifying agent. This helps the components mix.
• Lecithin, monoglycerides, diglycerides, and polysorbate 60
• So if the food label lists one of those things, it has lipids in it.
Recommendations for Fat Intake
• No RDA for total fat intake
• AHA recommendations
• 20-30% of total kcal from fat
• 7-10% can come from saturated/trans fat
• 200-300 mg cholesterol/day
• Average U.S. intake:
• 33% of total kcal from fat
• 13% of kcal from saturated fat
• 180-320 mg cholesterol/day
The American Heart Association
The American Heart Association
Advice from National Cholesterol Education Program and Food and Nutrition Board
• Up to 35% of total kcal from fat
• Keep saturated fat, cholesterol, and trans fat to a minimum
• Fat intake can be higher as long as saturated and trans fatty acid are minimal
• Eat plenty of fruits and vegetables
• Cut down on red meats
• Cut down on simple sugars and refined carbohydrate
• Promote healthy weight
• Be active
Cutting the Fat
Road to a Heart Attack
• Total blood cholesterol > 200 mg/dl
• Increases clotting
• Increases expression of genetic link
• Hypertension (> 139/89)
• Insulin increases cholesterol synthesis
• Guarantees development of cardiovascular disease
Other Risk Factors
• Low HDL (< 40 mg/dl)
• Family history
• Blood triglycerides > 200 mg/dl
• Fat around the waist
• Insulin resistance
Signs of a Heart Attack
• Intense, prolong chest pain
• Shortness of breath
• Nausea and vomiting
• Jaw, neck, shoulder pain
• Irregular heartbeat
• Medications to lower LDL
• Reduce cholesterol synthesis (Statins, “Lipitor”)
• Binds to bile acids or cholesterol for elimination
• Medications to lower blood triglycerides
• Reduce triglyceride synthesis
• See your doctor to assess for other conditions
• Reduce dietary saturated fat and cholesterol
• Increase MUFA and PUFA
• Increase fiber (soluble)
Lowering Blood TG
• Is the most diet-responsive blood lipid
• Avoid overeating
• Limit alcohol
• Limit simple sugars
• Small frequent meals
• Include fish in the diet
Other Possible Methods
• Benecol and Take Control margarines
• Plant stanol/sterol esters
• Cholesterol-lowering effects
• Decrease absorption of cholesterol and lower amount returning via enterohepatic circulation
• Liver takes up more cholesterol from the blood
• Physical activity
• At least 45 min/day, 4 days a week
• Don’t smoke
• Eat regularly
• Eat less total fat
• Moderate intake of alcohol increases HDL