Transcript Trans Fatty Acids - UK College of Agriculture

The Health Benefits of Fats
Quiz Yourself
True or False
1. To lose weight, use regular, stick margarine
instead of butter because it has 25% fewer
kilocalories per teaspoon. T F
2. Egg yolks are a rich source of cholesterol. T F
3. Taking too many fish oil supplements may be
harmful to health. T F
4. Increasing your intake of trans fats can reduce
your risk of heart disease. T F
How Did You Do?
1. False Regular stick margarine has about the
same kcal/teaspoon as butter.
2. True Egg yolks are a rich source of cholesterol.
3. True Taking too many fish oil supplements may
be harmful to health.
4. False The average American consumes about
1/3 of his/her daily energy intake from fat.
5. False Increasing your intake of trans fats may
increase your risk of heart disease.
A balanced picture of fats
• Is all fat bad for you?
Dietary Lipids
• Triglycerides—the major form of fat in food
• Phospholipids—similar to triglycerides in basic
structure; contain phosphate containing
groups
• Sterols—mainly cholesterol
• Fat-soluble vitamins (A, D, E, K)
• Some phytochemicals (carotenoids)
Triglyceride Properties
• Concentrated source of energy (9 kcal/gm)
• Source of essential fatty acids
• Required for absorption of fat soluble vitamins
by acting as a carrier in the small intestine
• Increase palatability and satiety value of foods
• Protection of organs and insulation
Triglyceride
Composed of
3 fatty acid
molecules
bonded
to a glycerol
molecule
• Composed of
carbon,
hydrogen,
oxygen
Triglyceride Properties
• Contain less oxygen than carbohydrates so
they contain more energy
• Insoluble in water –Require emulsification by
bile acids for adequate digestion
Triglycerides: Fatty Acids
• Fatty acids are composed of a chain of carbon
atoms with a carboxyl (acid) group at one end.
• Hydrogen atoms are bonded to the carbons.
– Carbon chain length can vary.
Fatty Acids: The three types of fatty
acids are present in most food fats
• Saturated
– Animal fats (milk products, butter, meat)
– Coconut oil
– Palm and palm kernel oils
• Monounsaturated
– Olive oil
– Canola oil
– Peanut oil
– Safflower oil
• Polyunsaturated
– Most vegetable oils except palm kernel and coconut oils
– Nuts, seeds
– Chicken, turkey, fish
Saturated Fat
• Saturated—no double bonds exist between
carbons; only single bonds between carbons
– Carbons are fully saturated with hydrogen atoms;
only single bonds exist between carbons
– Palmitic acid (16 carbons)—the most abundant
saturated fatty acid in foods
Unsaturated Fatty Acids
• Monounsaturated—one double bond in the
carbon chain
• Polyunsaturated—more than one double bond in
the carbon chain
• Short chain fatty acids — 2 to 4 carbons
• Medium chain fatty acids — 6 to 12 carbons
• Long chain fatty acids –- 14 to 24 carbons
Saturated fats
• Solid at room temperature
•
•
•
•
Butter
Lard
Vegetable shortening (Crisco)
Coconut oil
• Tend to raise blood cholesterol and increase heart
disease risk. Can also increase insulin levels.
• Lowering dietary fat can lower cholesterol levels.
Monounsaturated Fatty Acid
• One double bond exists in the carbon chain.
• Oleic acid (18 carbons, 1 double bond)—the
most abundant monounsaturated fatty acid in
foods
• Oleic acid is an omega-9 fatty acid because the double bond
occurs at the 9th carbon from the omega end of the
molecule
Monounsaturated Fatty Acids
(MUFA): Properties
• Liquid at room temperature
– Olive oil
– Canola oil
• Tend to lower blood cholesterol if they replace
saturated fat in the diet.
Polyunsaturated Fatty Acids
(PUFA): Structure
More than one double bond exists in the carbon
chain
Linoleic acid (18 carbons, 2 double bonds)
Linoleic acid is an omega-6 fatty acid because the double
bond occurs at the 6th carbon from the omega end of the
molecule. It’s also known as an n-6 fatty acid.
Polyunsaturated Fatty Acids
(PUFA): Structure
Another important PUFA
Linolenic acid (18 carbons, 3 double
bonds)
•Linolenic acid is an omega-3 fatty acid
because the double bond occurs at the 3
carbon from the omega end of the molecule.
It’s also known as an n-3 fatty acid
rd
Polyunsaturated Fatty Acids:
Properties
• Liquid at room temperature
– Most vegetable oils
• More chemically unstable
– Rancidity occurs more easily
• Tend to lower blood cholesterol and reduce
heart disease risk.
Food Sources of Fatty Acids
• Saturated
– Animal fats (milk products, butter, meat)
– Coconut oil
– Palm and palm kernel oils
• Monounsaturated
– Olive oil
– Canola oil
– Peanut oil
– Safflower oil
• Polyunsaturated
–Most vegetable oils except palm kernel and coconut oils
–Nuts, seeds
–Chicken, turkey, fish
Essential Fatty Acids
• Two essential fatty acids
– Linoleic acid (an n-6 fatty acid)
– Linolenic acid (an n-3 fatty acid)
• They are called essential because they
must be consumed to maintain good
health.
• Both essential fatty acids are
polyunsaturated.
Essential Fatty Acids—General
Functions
• Components of cell membranes
• Required for growth, reproduction, good skin
integrity and wound healing
• Precursors of eicosanoids
– Eicosanoids are elongated (20C) highly unsaturated
fatty acids
– Involved with reproductive functioning, immune
system integrity, cell growth
– Optimize eicosanoids in the body by consuming a
balanced ratio of essential fatty acids
Linoleic – n-6 Fatty Acid
• Unique properties
– Can reduce blood cholesterol and heart disease risk
– Does not reduce cancer risk
• Requirement: Minimum of 3% of total kcal or
a total of 60 kcal from linoleic acid. This
amount is supplied by 1 tablespoon of soy oil.
– Typical American diet provides 7% of kcal as linoleic acid.
– Excessive intakes can suppress the immune system
.
• Good food sources: most vegetable oils,
nuts, seeds, poultry, fish; small amounts in
egg yolk, whole grains.
Linolenic – n-3 Fatty Acid
• Unique functions and properties
– May be required for development of visual acuity
– Lowers blood triglycerides
– High intakes prolong bleeding time
– Anti-inflammatory properties
– Enhances the immune system
– May reduce heart disease and cancer risk: In
Japan, where n-3 fatty acid intake is much greater
than in the US heart attacks are four times less
common!
Linolenic Acid
• Requirement: Minimum of 0.5% of total kcal
or a total of 10 kcal from linolenic acid. This
amount is supplied by 1 tablespoon canola oil
• Good food sources: flaxseed, English walnuts,
canola oil, soy oil, ocean fish
• Also contained in egg yolk, dark green leafy
vegetables, whole grains
Linolenic acid
•
•
•
•
The ratio of dietary linoleic and linolenic
acids seems to be important for heart
disease and cancer prevention.
– N-6/n-3 ratio tends to be high in the
American
• diet (range from 10:1 to 50:1)
• – Recommended ratio 4:1
Ratio of Essential Fatty Acids
Achieving a balanced ratio of essential FAs usually
involves finding ways to increase linolenic acid
– Use primarily soy and canola oils (read food labels for
these)
– Avoid hydrogenated oils (these lower the essential fatty
acid content of vegetable oils)
– Avoid substituting reduced fat or fat free products for
products containing linolenic acid (salad dressings)
– Maintain eggs in the diet
– Use some flaxseed
– Eat dark green leafy vegetables very often
– May include ocean fish in the diet
Cis and Trans Fatty Acids
2 isomeric forms of fatty acids exist
– Cis and trans fatty acids have the same
chemical formula, just a different configuration
around the double bond.
Cis and Trans Fatty Acids
The TRANS configuration
Cis and Trans Fatty Acids
• The cis configuration occurs most often in nature
• Trans configuration
– Occurs naturally in small amounts in some foods (beef, lamb,
milk fat)
– Most trans FAs in foods are a byproduct of the industrial
hydrogenation of vegetable oils. Hydrogenation adds hydrogens
to unsaturated fatty acids to make them more saturated. This
improves the stability of vegetable oils and makes them more
solid at room temperature. In the
– process, the configuration of some double bonds changes from
cis to trans. Hydrogenation is used in the production of
margarine from oil.
hydrogenation
soybean oil
soybean margarine
Trans Fatty Acids
• Americans eat about 5 g trans fat/day
The problems with trans Fat
– Trans fatty acids do not relieve symptoms of essential fatty acid
deficiency. In fact hydrogenation destroys some of the essential
fatty acids in the oils. It also inactivates the vitamin K in the oil.
• Trans fatty acids act similarly to saturated fatty acids in
raising blood cholesterol and insulin levels.
• Although the amount of trans fatty acid in most foods is
less than the amount of saturated fatty acid, it is advisable
to avoid them.
Trans Fatty Acids (cont)
Minimize intake of trans fatty acids by limiting intake of
hydrogenated fats. Look for the word “hydrogenated” in
the list of ingredients on the food label.
– Use vegetable oils and softer margarines as
spreads and in recipes.
– Limit or avoid use of solid margarines, vegetable
shortening (Crisco).
– Limit or avoid high fat commercial baked goods—
donuts, muffins, cookies, cakes.
– Limit or avoid restaurant fried foods, high fat foods.
Summary- Types of Fats
Why would it be undesirable to eliminate
fat from our diet?
Answers
• We need essential fatty acids.
• Substrate for eicosanoid synthesis would be
reduced.
• A fat free diet would greatly reduce the
absorption of fat soluble vitamins and
carotenoids.
• Fat provides a concentrated source of kcal.
• Eliminating fat would make it difficult to maintain
a stable weight.
• Fat makes eating more pleasurable.
How can we obtain a healthful balance of
fatty acids in our diets?
Graphics: Microsoft Online, USDA Food and Nutrition Services
Ingrid Adams, Ph.D., R.D. L.D.
Associate Professor , Nutrition and Food Science, University of Kentucky
Extension Specialist for Physical Activity and Weight Management
Date: February 27, 2015
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