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Lipids
Dr. Mohammad Hasan Mostafa
M.B.Ch.B - Hawler Medical University
MMedSci Human Nutrition - UK

Lipids
• Lipids have been defined as substances that are generally
insoluble in water but soluble in organic solvents, such as
ether, acetone, and chloroform.
• Lipids are composed primarily of the elements carbon
and hydrogen; they contain fewer oxygen atoms than do
carbohydrates.
• Chemical energy that is derived from lipids is (9 kcal per
gram).

• Lipids that are solid at room temperature are referred
as fats.
• While, those are liquid at room temperature are called
oils.
• Lipids include:
‣ Triglycerides.
‣ Phospholipids.
‣ Sterols :
• Cholesterol.
• Phytosterols (plant sterols)

Functions
1. Supplying energy for the cells.
2. Providing essential fatty acids.
3. Being a carrier for fat soluble vitamins and antioxidants.
4. Insulating against heat loss by means of subcutaneous
fat stores.
5. Providing protective layer around essential organs.

6. Forming a structural component of brain tissue and
myelin sheath surrounding nerves.
7. Principal structural components of cell membrane are
phospholipids and cholesterol.
8. Cholesterol serves as the precursor for many steroids in
the body, including the bile acids, estrogens, androgens,
progesterone, adrenocortical hormones; and vitamin D.

Triglycerides
• Triglycerides are the primary and the major form of the
lipids in the body and the foods.
• Account for more than 95% of dietary fat.
• They are composed of glycerol, to which three fatty acids
are attached by ester bonds.
• The type of fatty acids present in a triglyceride determines
the physical characteristics, nutritional properties and
physiological effects of it.

Triglyceride structure

Fatty acids
• Fatty acids are the simplest form of the lipids.
• They are composed of a hydrocarbon chain with a methyl
group at one end and a carboxylic acid group at the other.
• The number of carbon atoms vary from 4-24.
• Most common Chain length is 16 and 18.
• About 21 fatty acids are found in the foods.

• Fatty acids can be saturated or unsaturated with
hydrogen ( present of double bond or not).
• Saturated fatty acids: no double bond.
• Monounsaturated fatty acids: one carbon–carbon double
bond.
• Polyunsaturated fatty acids: two or more carbon–carbon
double bonds.
• Fats in foods are not composed of a single type of fatty
acid.

CH3
CH2
COOH
Methyl end
Carboxylic
acid end
CH

Fatty acid nomenclature
• There are two notation systems that summarize the
chemical structure of a fatty acid.
1. The delta (Δ) system of notation: 18:2 Δ 9,12
• Denotes the chain length of the fatty acids, the number and
position of any double bonds that may be present.
• The first number represents the number of carbon atoms.
• The number following the colon refers to the total number
of double bonds present.

• The superscript numbers following the delta symbol
designate the carbon atoms at which the double bonds
begin, counting from the carboxylic acid end of the
fatty acid.

2. Omega (ω) notation system: 18:2 ω-6 or 18:2 n-6
• In this system, the total number of carbon atoms in
the chain is given by the first number.
• The number of double bonds is given by the number
following the colon.
• The location (carbon atom number) of the first double
bond counting from the methyl end is given by the
number following ω or n.

Saturated fatty acids
• The carbons that make up the chain of a saturated fatty
acid are all connected to each other by single bonds.
• The saturated fatty acids are very straight and linear and
therefore can pack very close together.
• This close packing or stacking of saturated fat
molecules makes them solidify at room temperature.
• They have relatively high melting point.

• They tend to raise the level of LDL cholesterol in the
blood.
• high intake of saturated acids increases the risk of
cardiovascular diseases.
• They are mainly derived from animal food sources like
meat fat, milk, butter and cheese.
• Foods of plant origin have a much lower content of
saturated fats with exception for coconut and palm oil.

Monounsaturated fatty acids
• Fatty acids containing one carbon-carbon double bond.
• They are usually liquid at room temperature.
• They are regarded as most beneficial type of fatty acids
that tend to decrease the level of LDL cholesterol in the
blood.
• The most concentrated dietary sources are olive oil,
canola oil, peanut oil, rapeseed oil, avocado and nuts.

Polyunsaturated fatty acids
• fatty acids that are containing two or more carboncarbon
double bonds.
• They are usually liquid at room temperature.
• Are susceptible to oxidation within the foods and
body.
• Polyunsaturated fatty acids are divided into:
Omega-3 polyunsaturated fatty acids
Omega-6 Polyunsaturated fatty acids.

Omega-3 polyunsaturated fatty acids
• They are unsaturated fatty acids with the first double
bond on the third carbon from the methyl end (−CH3).
• Include α-linolenic acid (essential fatty acid),
eicosapentaenoic acid (EPA) and docosahexaenoic acid
(DHA)
• They can reduce triglyceride concentration in the blood.
• They have anti thrombotic and anti inflammatory effects.

• EPA and DHA have an important structural in brain,
retinal and nervous tissues.
• Flax seeds, walnuts, chia seeds, canola, and soybeans are
the rich sources of α-linolenic acid .
• EPA and DHA can be made in the body from α- linolenic
acid .
• These two omega-3 fatty acids are naturally found in
fatty fish such as salmon, tuna, sardines, herring,
mackerel and trout.

Omega-6 polyunsaturated fatty acids
• They are unsaturated fatty acid with the first double
bond on the sixth carbon from the methyl end (−CH3).
• Linoleic acid (essential fatty acid) is regarded as a
main form of omega-6 polyunsaturated fatty acids.
• They also include γ-linolenic acid and arachidonic acid
(AA), which are present in small amount in foods and
mainly synthesised from linoleic acid.

• AA is a component of cell structure and has an
important structural in brain, retinal and nervous
tissues.
• They reduce blood LDL cholesterol, but excessive
intake ( more than 10% of energy) can reduce HDL.
• Are susceptible to oxidation within the foods and
body.
• When oxidation of them occurs in food products, the
food develops an unpalatable flavor and odor.

• While, when they oxidised in the body can cause
inflammation and tissue damage.
• This process is thought to contribute to aging,
atherosclerosis, and cancer.
• Thus, dietary intake of them must be adequate not
excessive.
• Linoleic acid mainly derived from soybean oil, corn
oil, sunflower oil and safflower oil.

Essential fatty acids
• Fatty acids that must be supplied by the diet to maintain
health.
• Two polyunsaturated fatty acids are essential in the human
diet which are linoleic acid (an omega-6 fatty acid) and
α- linolenic acid (an omega-3 fatty acid).
• Human enzymes convert the two essential fatty acids to
other long-chain polyunsaturated fatty acids, EPA , DHA
and AA.

• AA, EPA and DHA have important structural role
and involved in immune function and vision.
• They produce eicosanoids, which are involved in
important functions in the body.
• The eicosanoids that derived from AA are more pro
inflammatory, while those from EPA and DHA are
more anti inflammatory.

Linoleic acid α- linolenic acid
Δ6 desaturase
γ-linolenic acid
Eicosapentaenoic acid
Arachidonic acid
Docosahexaenoic acid
Eicosanoids
pro inflammatory
Eicosanoids
anti inflammatory

Cis and Trans configuration
• The orientation of hydrogen atoms about a double bond
influences the structure and thus the physical properties
of a fatty acid.
• If the hydrogens associated with the carbons of a double
bond are positioned on the same side, it is a cis
arrangement.
• In contrast, if the hydrogens bonded to the carbons are on
opposite sides of the double bond, it is a trans
arrangement.

• In nature, monounsaturated and polyunsaturated fatty
acids usually are in the cis form.
• Trans fatty acids may be natural (conjugated linoleic acid)
which is rare or industrial trans fatty acid.
Cis and Trans configuration

Conjugated Linoleic Acid (CLA)
• Itis a family of fatty acids derived from linoleic acid.
• The bacteria that live in the rumens of some animals
(cows, sheep, and goats ) it from the polyunsaturated
fats in the grass the animals are fed.
• Found in meat, milk and butter.
• CLA improves insulin levels in diabetics and decreases
the risk of heart disease, cancer, and obesity.

Industrial trans fatty acids
• Produced when polyunsaturated fatty acids in liquid
vegetable oil are artificially hydrogenated (partially)
to make shortenings and margarines.
• They decrease HDL and increase LDL cholesterol.
(Hydrogenation)

Phospholipids
• They are phosphate containing lipids.
• composed of glycerol backbone, two fatty acids, and a
phosphate (PO4 ) group.
• They are an important part of cell membranes.
• Generally, phospholipids are unavailable as an energy
source.
• The body is able to produce all the phospholipids it needs,
so they are not essential.

• Lecithin is a common phospholipid which is used as a
dietary supplement and an additive in many foods.
• Wheat germ, peanuts, egg yolks, soybeans, and organ meats
are rich sources of phospholipids.

Cholesterol
• It is a waxy like substance, characterized by having a fourring
steroid nucleus that makes them structurally and
functionally different from the other lipids.
• It can exist in free form or can be esterified with a fatty
acid.
• It is structural component of cell membranes and myelin
sheaths.

• Cholesterol serves as the precursor for many important
steroids in the body, including the bile acids, estrogens,
androgens, progesterone, adrenocortical hormones; and
vitamin D.
• The body can make all the cholesterol it needs, so it is not
essential components of the diet.
• Eating more dietary cholesterol leads to reducing synthesize
by the liver.
• Eggs, meats, whole milk and offal are dietary sources of
cholesterol.

Phytosterols (plant sterols)
• Phytosterols are structurally similar to cholesterol, with
only slight differences in the side chain.
• They are component of plant cell membrane.
• Phytosterols are found plant oils, legumes, nuts, and seeds.
• Decrease the amount of cholesterol available for intestinal
absorption.

Food sources

Recommended Intakes
• It is recommended that fat intake should be 20% to
35% of total daily energy requirement.
• Saturated fatty acids: less than 10%.
• Omega-6 polyunsaturated fatty acids: 5 – 10%.
• Monounsaturated fatty acids: 10 -20%
• Omega-3 polyunsaturated fatty acids:
• α-linolenic acid : Men (1.6 g/d) , women (1.1g/d)
• EPA and DHA: Two serving of fatty fish per week.