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LIPIDS & FATS

Dr. Mehak Ashfaq
MSPH-NS
Lecturer, Bs- Human Nutrition and Dietetics
FEM, HU
Lecture No. 6
Macronutrients in Human Nutrition
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Outline
• Definitions- Fats & Lipids

• Fatty Acid- structure

• Types of Fats & Lipids

• Functions

• Dietary Sources
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Learning Objectives
• Define the structure and illustrate the concepts related to
lipids in food and nutrition

• Identify types & quality of lipids based on their fatty acid

structure

• Classify essential and non essential fatty acids

• Describe the functions and food sources of lipids

Lipids- Definition
• “Lipid” is synonymous with “fats” “oils”

• Group of organic compounds

• Composed of carbon, hydrogen and oxygen
• Generally insoluble in water
• A lot of calories in a small space (9 kcal/gm)
Structure

• A molecule of fat is
composed of chains of
carbon atoms
• 1unit of Glycerol + 3
Fatty Acids (FA)
• FA are organic
molecules and the
most abundant lipids
Types of FA (length of Carbon chains )
• Short Chain FA
• 2-6 carbons
• Butyric acid (butter)

• Medium Chain FA
• 6-10 carbons
• Lauric & capric acid (coconut oil, palm oil & ghee)
• Lower levels in Dairy products

• Long Chain FA
• 12 or more carbons
• Most common in foods (18-C FA)
• Palmitic, oleic, stearic acid
• FA of meats, fish, & vegetable
oils
 Types of FA(Degree of saturation/unsaturation)
• Saturated Fatty Acids
• Fully loaded with hydrogen atoms
• Only single bonds between carbon atoms

• Unsaturated Fatty Acids

• When 2 Hydrogen or more are missing from the middle of the
carbon chain,
• Compound cannot exist, nature requires that every Carbon
have 4 bonds,
• Two carbons form double bond to exists.
• Monounsaturated Fatty Acids (MUFA) → 1 double bond
• Polyunsaturated Fatty Acids (PUFA) → 2+ double bonds
• The double bond is the point of unsaturation
Difference between FA (Saturation)
Degree of Unsaturation (Firmness)
• Influences the firmness of fats at room temperature

• Saturated animal fats are solid at room temperature

• PUFA vegetable oils are liquid at room temperature

• All vegetable oils are not necessarily liquid at room

temp for e.g cocoa butter, coconut oil, palm oil are
saturated & firmer but softer than animal fats

• The reason for being softer is shorter chain of

carbon (8-14)
Degree of Unsaturation (Stability)
• Saturation influences stability
• Fats spoils when exposed to oxygen
• PUFA can spoil more easily because their double
bond are unstable
• MUFA are less easily spoiled
• Saturated fats are resistant to oxidation & least
likely to become rancid
• Oxidation is the process of a substance
combining with oxygen & losing Hydrogen
/Electrons
 Rancidity

• Oxidation of fats producing compounds/chemicals

• Causing unpleasant smells in fats & oils
• Change in texture & appearance of fats
• Spoilage in fats due to microbial growth
• Fat and oil manufacturers have to prevent rancidity by
various processes
How do manufacturers Prevent Rancidity?
• Sealing in air tight, non-metallic containers,
protected from light & refrigerate (expensive &
inconvenient)
• Add anti-oxidants to compete for the oxygen &
protect the oil (vit E & other additives)
• Saturate some or all points of unsaturation by adding
hydrogen molecules (Hydrogenation)
• Hydrogenation is a chemical process by which
hydrogens are added to MUFA or PUFA to reduce the
number of double bonds
Hydrogenation
Advantages
• Makes the fat more saturated & therefore prolong
shelf life by making it more resistant to oxidation &
rancidity
• Alters the texture of foods by making liquid
vegetable oil more solid (margarine & shortening)
Disadvantages
• Hydrogenation produces more trans-fatty acid
• Trans-FA has fatty acids with hydrogen on opposite
sides of the double bond
Trans Fatty acids
• When a double bond occurs in a fatty acid, the hydrogen
atoms can either be on the same side of the chain (called
the cis confirmation) or on the opposite side of the chain
(called trans)
• In the cis formation, the FA has its hydrogen on the same
side of the double bond & has a bend
• In the trans formation, the FA has its hydrogen on the
opposite sides of the double bond & molecule is straight

• A change in the orientation of one double bond makes

trans fatty acids physically and physiologically different
from the more natural cis fatty acids
Formation of Trans Fatty Acids
• When manufacturers turn liquid oils into solid fats
• Hydrogenation process
Types of FA( Location of double bonds)
Position of the double bonds
• PUFA can be identified by the position of their
double bond
• First double bond from the methyl group (CH3)
end of the carbon chain is called omega
• First double bond 3 carbons away from methyl
end is an omega-3 FA ( Linolenic fatty acid)
• First double bond 6 carbons away from the
methyl end is omega-6 FA (Linoleic fatty acid)
• Omega number indicates the position of the first
double bond
• Whether to call a fatty acid saturated, unsaturated,
monounsaturated, polyunsaturated, or trans fatty
acids is determined by its chemical bonds and
structure
Classes ofLipids
• Triglycerides (fats & oils)
• Main fat form found in body
• Main dietary fat form
• 1 glycerol + 3 fatty-acid chains
• Phospholipids (i.e. lecithin)
• 1 glycerol + 2 Fatty acids + Phosphate group + choline
• Soluble in both fat (FA) & water (phosphate group)
• Component of cell membranes & aids in emulsification
• Sterols (i.e. cholesterol)
• Compounds with 4-ring C structures + a variety of side
chains.
• Numerous important roles: bile acids, sex hormones,
adrenal hormones, vitamin D and cholesterol
Classes oflipids

fatty acids
Triglycerides
• Few FA occur free in foods or in the body
• Incorporated into triglycerides
• Composed of 3 FA attached to a glycerol
• To make a Triglyceride, a series of Condensation reaction
combine a hydrogen (H) atom from the glycerol & a hydroxyl
(OH) from a fatty acid, forming a molecule of water (H2O),
leaving a bond between other two molecules

• In the body TG provides energy reserve when stored in the

body‟s fat tissue
Phospholipids
• The Phosphate group is soluble in water, while the FA
„tails‟ are not
• Phospholipids are hydrophilic at 1 end & hydrophobic at
the other end
• Food sources ( egg yolks, liver, soybeans, peanuts)
Phospholipids Main building blocks of cell
membranes
• Help lipids move back & forth
across the cell membranes
into the watery fluids on both
sides
• Enable fat-soluble vitamins &
hormones to pass easily in
and out of cells
Phospholipids (Lecithin)
• Receives most attention
• It is not the essential
nutrient
• Large doses can cause GI
pain, sweating,& loss of
appetite
Glycerol (Sterols) Sterols are a family of molecules of
interconnecting multiple carbon rings

• Important body compounds are

sterols
• Both plants & animals contain
sterols
• The most common form of sterol is
Cholesterol
• Animal sources has significant
amount
• Plant sterol interfere with Cholesterol
cholesterol absorption, thus
lowering blood cholesterol
Cholesterol Facts
• Liver makes about 800-1500 mgs of cholesterol
per day
• Component of cell membranes
• Precursor to other substances
• Steroid hormone
• Vitamin D
• Bile acids
Food Sources
• Only animals ( meats, eggs, fish, poultry, prawns)
• Organ meats (3 oz liver/337 mg)
• Egg yolk (1 egg/212mg)
• Dairy products (1 cup milk/25-30 mg)

• Fish (3 oz/25-30 mg)

Cholesterol in Foods
Lipids- Functions
Two major roles in the body

• Oxidation of FA – major means of metabolic energy

production

• Storage of FA as TG – more efficient and quantitatively

more important than storage of CHO as glycogen
Lipids- Functions
• Major source of FUEL & ENERGY (9kcal/gm)

• Help the body use CHO & Protein efficiently

• Form cell membranes

• Insulation (body organs, temp extremes, shock)

• Aid in absorption of fat-soluble vitamins (A,D,E,K)

• Provide starting material for hormones (cholesterol)

Body Composition
Fat- Major source of Fuel & Energy
• For example in the non-obese 70 kg. man, 13.5 kg. of fat
will carry 130,000 to 160,000 kcal. while 13.5 kg. of
muscle will carry only 54,000 kcal
Food Contain various FA
• Monounsaturated Fatty Acids (MUFA)
• Olive, peanut & Canola oils

• Omega-6 Polunsaturated fatty acids (PUFA)

• Safflower, corn & sunflower oils

• Omega-3 PUFA
• Fish, seafoods, nuts, flax seeds & some vegetable oils

• Saturated Fatty Acids (SFA)

• Meats, butter & regular dairy products, palm & coconut oil
Essential FattyAcids
1. Linoleic acid (18- Carbon omega-6 FA)
2. Linolenic acid (18- Carbon omega-3 FA)

• These two must be supplied by the diet and therefore are

called Essential Fatty Acids
Essential FattyAcids
• Linoleic acid (18 C, omega-6)
• Found in vegetable oils and meats
• Only need ~ 1 tablespoon a day
• Arachidonic acid can be made from omega-6
• Linolenic acid (18 carbons, omega-3)
• Found in Fatty fish,canola or soybean oil
• Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)
• Metabolized to form eicosanoids
• Recommended intake : ~2 servings of fish per wk
Recommended Intakes
• No RDA or upper limits on fat intake has been set
• 30% kcal from fat
• <10% from saturated fat
• Low in saturated fat, trans fat, cholesterol

• Dietary saturated fat, cholesterol and trans fats increase

serum cholesterol and serum LDL-C levels
• PUFA and MUFA appear to decrease serum total
cholesterol and LDL levels
• But REMEMBER PUFA also decrease HDL levels
Comparison of DietaryFat
Saturat Linole Alpha- Monousatura
DietaryFat
ed ic Linoleni ted Fat
Fat Acid c Acid
CornOil 13% 61% 1% 25%
Olive Oil 14% 8% 1% 77%
SoybeanOil 15% 54% 7% 24%
Peanut Oil 18% 34% 0% 48%
SafflowerOil 9% 78% trace 13%
Sunflow
11% 69% 0% 20%
er Oil
Palm Oil 51% 10% 0% 39%
Lard 41% 11% 1% 47%
Beef Tallow 52% 3% 1% 44%
Butterfat 66% 2% 2% 30%
CoconutOil 92% 2% 0% 6%
How can we improve our diet?
• Milk and milk products
• Fat free and low fat milk provides the same or more protein,
calcium as whole milk
• Fermented milk products may lower blood cholesterol
• Vegetables, Fruits, Grains
• Lower the content of saturated fat, cholesterol, and total fat
• Fill up on these little or no fat foods

• Invisible Fat
• Can you suggest the sources of this in Pakistani foods
Sources

• “Understanding Nutrition” 11th Edition-2011

• Ellie Whitney & Sharon Rady Rolfes

• “Krause‟s Food & Nutrition” 12th Edition2008

• Mahan & Escott-Stump