notes on fat

1. FATS/LIPIDS

2. DEFINITION
 Lipids are heterogeneous group of compounds which
are relatively insoluble in water
soluble in organic solvents like other, benzene, alcohol,
chloroform etc

3. CLASSIFICATION OF LIPIDS
Lipids are classified into 3 major classes, based 0n
their composition.
• Simple lipids
• Compound lipids
• Derived lipids

4. SIMPLE LIPIDS:
 Simple lipids are esters of fatty acids with alcohols. They
do not contain any conjugate groups.
They are two types
a) Fats/ oils
b) Waxes
Fats/oils :They are the esters of fatty acids with glycerol
Waxes: Waxes are esters of fatty acids with higher alçohols.
E.g.: Bee wax, carnauba wax, wool fat (lanolin),

5. COMPOUND LIPIDS
 They contain conjugate groups in addition to fatty
acids & alcohols.
 These include
phospholipids,
glycolipids,
sulpholipids etc.

6.  Phospholipids: These are compounds lipids containing
phosphoric acid residue as
conjugate group.
Phospholipids are of two types,
i) Glycerophospholipids: E.g.: Lecithin, Cephalin, Plasmalogen
etc
ii) Sphingophospholipids: E.g.: Sphingomyelin of myelin
sheath of nerves
b) Glycolipids: These are compounds lipids containing
carbohydrate residues
.
Glycolipids are two types,
i) Cerebrosides: E.g.: Kerasin, cerebron, nervon, & oxynervon
ii) Gangliosides: E.g.: GM1, GM2, GM3, GM4 etc

7. DERIVED LIPIDS
 These are the products or precursors of simple &
compound lipids.
Examples: Fatty acids, cholesterol, steroid
hormones, fatty alcohols, Ketone prostaglandins
etc,

8. FATTY ACIDS
fatty acids are the main building blocks of all simple
lipids and compound lipids
Fatty acids are divided into two groups based on the
nature of hydrocarbon chain
i) Saturated fatty acids
ii) unsaturated fatty acids

9. SATURATED FATTY ACIDS:
They do not have any double bond in their hydrocarbon
chain
Example:
Acetic acid Propionie acid
butyric acid Valeric acid
Caproic acid Caprylic acid
Capric acíd Lauric acid
Myristicacid Palmitic acid
Stearic acid Arachidic acid

10. UNSATURATED FATTY ACIDS
Unsaturated fatty acids have double bonds in their
hydrocarbon chain.
subdivided into two types based on the number of
double bonds.
a) Monounsaturated fatty acids [MUFA]
b) b) Polyunsaturated fatty acids [PUFA):

11. Monounsaturated fatty acids [MUFA]:
These contain only one double bond in their structure.
Examples are
palmitoleic acid,
oleic acids etc.
Palmitoleic acid
Oleic acids
Polyunsaturated fatty acids [PUFA):
These contain more than one double bond in their structure.
Examples are
Linoleic acid - 2 double bonds
Linolenic acid - 3 double bonds
Arachidonic acid - 4 double bonds
Timnodonic acid - 5 double bonds
Cervonic acid -6 double bonds.

12. DIETARY SOURCES OF FATTY ACIDS:
Fatty acids are mainly present as constituents of fats/oils
or compound lipids
Acetic acid is present in the vinegar.
Butyric acid, Valeric and Caproic acids present in butter.
Lauric acid and myristic acid are present in vegetable oils
(Especially in coconutand palm oil) and also in butter.
Stearic acid is present in most vegetable and animal fats
Palmitoleic acid is present in olive oils, fish oils and beef .
Oleic acid is widely distributed in all fats and oils .
Arachidonic acid, Timnodonic acid and Cervonic acid are present
in fish liver oil and shell fishes
Trans fatty acids are mainly present in Vanaspati,Margarines,
deep dried fast foods , cake mixes, chips and crackers, whipped
toppings, packaged candy, cookies doughnuts, pies and cakes
etc.

13. ESSENTIAL FATTY ACIDS:
The fatty acids, which are not synthesized in the
body, hence have to be supplied in the diet are
termed as essential fatty acids
Linoleic acid,
- linolenic acid
arachidonic acid
Dietary sources:
Essential fatty acids are mostly found in vegetable
oils (Except coconut oil and palm and fish liver oils )

14. ESSENTIAL FATTY ACIDS:
Functions:
Eicosanoid synthesis: Essential fatty acids serve as precursors of
eicosanoids, which function as local hormones.
Lipid transport: Essential fatty acids are required for the synthesis of
phospholipids
Lowering serum cholesterol: Essential fatty acids reduce serum
cholesterol levels.
Normal Epidermal growth: Essential fatty acids are required for the normal
reproductive function
Normal reproductive function: Essential fatty acids are required for normal
epidermal growth
Deficiency
Phrenoderma:It is characterized by horny papular eruptions on the
posterior and lateral parts of thigh and on the back and buttocks
Deficiency of EFA may also causes reproductive failure

15. DIETARY SOURCES OF FATS /OILS
Vegetable oils (Ground nut oil, coconut oil, mustard oil, sunflower
oil)
Vanaspati, margarines
Milk and milk products like Ghee, butter, cheese
Meat, fish, poultry, egg yolk etc
Fats are present in almost all food articles (Except sugars) in
small amounts.
Visible fats are those that are separated from their natural source and
visible to the naked eye. Example; cooking oils (vegetable fats/oils) from
oil bearing seeds and nut,ghee and butter from milk etc. It is easy to
estimate the amount of their dietary intake.
Invisible fats are hidden and are not visible to the naked eye as
they found in small quantity in almost all food materials. For
instance, foods like cereals, pulses, nuts, tubers contain small
amounts of fats,

16. SATURATED FAT AND UNSATURATED FAT
a) Unsaturated fats (Mainly vegetable fats):
• Unsaturated fats contain relatively more of unsaturated fatty acids
and less of saturated fatty acids
• They are liquid or soft at room temperature.)
• They have low melting points.
• They are susceptible to rancidity when exposed to light and
oxygen over a prolonged period. Rancidity results in an offensive taste
and smell.
• They are predominately found in vegetable fats/oils (with the
exceptions of coconut, palm, and palm kernel oils). In contrast, fish
oils, although they are termed as animalfats, contain large amounts of
unsaturated fatty acids

17. SATURATED FAT AND UNSATURATED FAT
Saturated fats (Mainly animal fats):
• Saturated fats have relatively more of saturated fatty
acids and less of unsaturated fatty acids
• They are solid at room temperature. Exceptions to this
generalization are coconut oil and palm oils (tropical oils)
• They have high melting points
• They are more stable than unsaturated fats.
• They are predominately found in animal fat/oil, except
for the coconut oil and palm oils

18. RANCIDITY OF FATS
Fats and Oils have a tendency to become rancid (stale) on
standing. The term rancidity
refers to the appearance of unpleasant smell and taste for fats/
oils.
Two types:
Hydrolytic rancidity:Is due to partial hydrolysis of triacylglycerols
by the enzyme lipaes present in naturally occurring fats / oils.
Oxidative Rancidity: The Oxidative Rancidity is a result of
oxidation of unsaturated fatty acids (present in triglycerides) to
form lipid peroxides, epoxides and aldehydes peroxidases and
free radicals. These products have an unpleasant taste and
odor
Unsaturated fats are more susceptible to oxidative rancidity.

19. HYDROGENATION
Process of converting unsaturated fat to saturated fat is
called hydrogenationin the presence of catalysts like
nickel or cobalt and at high temperatures, unsaturated
fatty acids present in fats/oils can accept hydrogen at the
double bonds and become saturated.
Example:
Vanaspati is prepared mainly from hydrogenation of
groundnut oil to which 5% sesame oil is added.
Margarine which is used as a cheap substitution of butter
mainly in western countries is prepared from
hydrogenation of vegetable oils like coconut oil and
ground nut oil. The heated oil is churned with skimmed
milk.

20. HYDROGENATION
Nutritional importance of hydrogenation
Hydrogenation improves the stability of a fat or oil, change its texture and
increase its functionality, The main advantage of hydrogenation is it change
of consistency,where the liquid vegetable oils are converted to odorless semi
solid and solid fats that are easy to pack, store and transport.
Since vegetable oils are deficient in vitamin A, hydrogenated fats
(vanasapai margarines) are fortified with vitamin A and D
Hydrogenation also prevents rancidity. So, storage quality
improves.
During hydrogenation process, some of the remaining unsaturated
fatty acids vegetables oils are altered from cis to trans form.
The principle oil used for hydrogenation are vegetable oils (usually
groundnut, corn, Soy bean, cotton seed, canola oils etc), which are
rich in linolenic acid. Linolenic acid is hydrogenated to oleic acid,
elaidic acid and stearic acid.

21. REFINED OILS
Raw oils are refined in order to remove the free fatty acids and
rancid materials.
Refining does not bring about any change in the unsaturated
fatty acid content of the oil. It only improves the quality and
taste of oils.
• Refined oils are free from odor and color.
• Refined oils are costly.
Refining usually consists of 3 processes.
i) Treatment with alkali to remove free fatty acids
ii) Treatment with steam to remove the odor
(Deodorization)
iii) Bleaching to remove the coloring matter

22. CHARACTERIZATION OF FAT / OILS
1) Saponification number
Saponification number of fats / oils is defined as the number
of milligrams of alkali (like KOH) required to saponify one
gram of fat/oil completely.
Significance:
Saponification number is an indication of molecular
weight of fat/oil.
Saponification number is inversely proportional to the
average molecular weight of fat/oil. Higher the
saponification number, lower the molecular weight of fat /oil

23. CHARACTERIZATION OF FAT / OILS
2) Iodine number
lodine Number of fat/oil is defined as the number of grams
of Iodine taken up by 100 grams of fat/oil.
Signifance
lodine number is an index of degree of unsaturation of fats
and is directly proportional to the content of unsaturated
fatty acids.
Higher the Iodine number of fat/oil, higher the degree of
unsaturation.
Example: iodine number of coconut oil = 6 to 10; Sunflower
oil = 124 to 136 . So this indicates Sunflower oil has higher
degree of unsaturation

24. FUNCTIONS OF FAT / LIPIDS
Biological role of fats in the body
Provision of energy:
Fats are the concentrated form of energy. But fats are not the
body's preferred fuel.
Storage of energy:
Stored fat in adipose tissues are the largest and efficient energy
reserve than glycogen. Glycogen storage accompanies water, so
it takes more space than fats which does not accompany water.
Glycogen storage capacity is limited, but fat storage capacity is
virtually unlimited. Glycogen stores last for only half a day, but fat
reserves can last up to 2 months.
Heat insulators:
The fat stored subcutaneously serves as an insulator against
heat loss to the environment. Fats also act as heat insulator
against the cold.
Shock absorbers:
The subcutaneous fat deposits also insulate against mechanical
trauma (act as shock absorbers), Fats deposits around the
internal organs insulate and cushion them and protect them from
mechanical injury.

25. FUNCTIONS OF FAT / LIPIDS
Dietary role of different lipids
1) Role of fats / oils in diet:
Source of energy: Dietary fats provide energy. They contribute up to 20 to 30% of daily
energy requirement
Taste: Oils / Fats increase the taste and palatability of the food. They absorb flavors and
aromas of ingradients to improve overall taste.
Satiety: Fats increase the satiety value of the food because of their slow digestibility and
increase in emptying time of stomach.
Smooth mouth feel: Fats / oils provide creamy and smooth mouth feel.
Dietary fats are the only sources of essential fatty acids: Absolute requirement of fats
in the diet is not for energy, but for the provision of essential fatty acids. Essential fatty
acids are required for eicosanoids synthesis and are important for epidermal growth,
reproduction and promoting normal growth in children and cell membrane formation
Digestion and absorption of fat soluble vitamins; Fats act as vehicles for the digestion
and absorption of fat-soluble vitamins and thus they promote the digestion and
absorption of fat-soluble vitamins.

26. FUNCTIONS OF FAT / LIPIDS
2) Functions of other dietary lipids
5% of dietary lipids is made up of phospholipids and cholesterol
A. Phospholipids:
Phospholipids are not essential in diet as they are
synthesized in the body.
Phospholipids also provide almost 9 Kcal /gram of energy,
like fats.
Phospholipids are required for the formation of cell
membranes, lipoproteins(transport form of lipids), blood
clotting etc.
Dietary sources:
Phospholipids occur naturally in almost all foods; excellent
sources are eggs, wheat germ and peanuts.

27. FUNCTIONS OF FAT / LIPIDS
B. Cholesterol:
• Cholesterol also forms a part of a balanced diet.
• Cholesterol is not an essential nutrient as it can be
synthesized in the body, A human being requires around 800
milligram of cholesterol per day. Out of this, about 300 mg
generally provided by diet and rest can be synthésized in the
body
• Cholesterol does not provide energy. But cholesterol is
required for synthesis of bile salts, vitamin D and variety of
steroid hormones.
.They are also important constituents of cell membranes.
Dietary sources of cholesterol:
Present in all animal foods, particularly rich in eggs.

28. CALORIFIC VALUE OF LIPIDS (FATS)
 The calorific value of fats is 9 Kcal/g (i.e. when one gram of fats is
oxidized in the body, 9 Kcal of energy is liberated)
 Daily requirement (RDA) of lipids (fat)
It is recommended that lipids (mainly fats) provide about 20 % of the
total daily energy requirement of the body.
RDA for lipids for adults is about 0.8 gram/kg body
weight/ day (About 40 - 50 grams for a 60 kg person). A minimum
requirement of 25-30 grams of lipids is essential to meet the
requirement of essential fatty acids and utilization fat- soluble vitamin
Cholesterol also forms a part of a balanced diet. Diet should contain
less than 300 mg of cholesterol.
Phospholipids are not essential in diet as they are synthesized in the
body.

29. DIGESTION, ABSORPTION, STORAGE AND
METABOLISM OF LIPIDS:
Digestion of lipids
More than 90% of the dietary lipids are fats and oil
lipids are insoluble in water and lipid digesting
enzymes are in water medium. This problem is overcome
by emulsification of fats by bile salts in the intestine
Very little digestion takes place in mouth and hence lingual lipase
cannot act on them

30. A. DIGESTION OF TRIACYLGLYCEROLS (FAT)
i) Digestion in the Stomach:
Lingual and gastric lipases initiate lipid digestion
by hydrolyzing triacylglycerols to form mainly
1, 2 diacylglycerols and free fatty acids
retention time of 2-4 hours in stomach, up to
30 % of fats can be digested in stomach.
Peristaltic contractions of stomach emulsify lipids for some
extent

31. DIGESTION OF TRIACYLGLYCEROLS (FAT)
ii) Digestion in the Intestine:
Pancreatic lipase enzyme hydrolyses triglycerides
in the intestine
the alkaline content of the pancreatic juice and biliary
secretion neutralizes food & changes the pH and
helps the action of pancreatic lipase.
Bile also contains bile salts, which emulsify fats in the
intestine

32. DIGESTION OF TRIACYLGLYCEROLS (FAT
Action of pancreatic lipase
pancreatic lipase hydrolyses triglycerides in the intestine.
Colipase, a protein secreted by
pancreas, acts ads cofactor for pancreatic lipase
lipase
Triacylglycerol 1,2 diacylglycerol+ fatty acids
colipase
lipase colipase
2 monoacylglycerol+ fatty acids
isomerase
1 monoacylglycerol
lipase colipase
glycerol + fatty acids

33. B) Digestion of Cholesterol ester and Phospholipids
Pancreatic secretion contains cholesterol esterase
and phospholipase
i) Cholesterol esterase hydrolyzes cholesterol ester
to cholesterol and fatty acid.
ii) Phospholipase A, hydrolyzes phospholipids to
lysophospholipid & fatty acid.

34. Absorption of lipids:
The water-soluble products of lipid digestion like glycerol
as well as small and medium
chain fatty acids are directly absorbed from the intestinal
lumen in to the portal vein and
taken to the liver and immediately utilized for energy
The water-insoluble products like 2-monoacylglycerols,
long chain fatty acids & cholesterol, phospholipids and
lysophospholipids are Incorporated into bile salt micelles
and absorbed into the intestinal cells.

35. Metabolism of lipids
Lipolysis: Fatty acids are rich sources of energy.
Triacylglycerols are the storage form of fatty acids, which
are stored in adipose tissues. During the conditions of
restricted diet (like
starvation and diabetes mellitus), the stored triglycerides
are broken down to glycerol
and fatty acids by lipases. This process is called lipolysis.
Fatty acid utilization
Fatty acids released from adipose tissue are transported
to tissues such as skeletal tissue,
heart muscle, renal cortex, which utilize fatty acids as a
source of energy by beta oxidation.

36. Lipogenesis and storage of fat:
When excess of glucose are consumed in the
diet, the surplus energy is first converted to
glycogen and then to fatty acids.
Fatty acids are then stored in the form of
triacylglycerols in adipose tissues.
Ketone bodies
Liver produces ketone bodies (by ketogenesis),
which are utilized by extrahepatic tissues
(by Ketolysis). In starvation and diabetes, liver
produces excess of ketone bodies, which
finally lead to ketosis.

37. Cholesterol:
Body requires around 1000mg (1g) of cholesterol per day. About 500 mg of cholesterol is
synthesized in a day and other 500mg is provided by diet.
Lipoproteins (Transport of lipids):
Lipoproteins are the combination of lipids and proteins.
There are four lipoproteins;
Chylomicrons,
VLDL (Very low density lipoprotein),
LDL (Low density lipoprotein),
HDL (High density lipoproteins). These contains variable amount of
triglycerides,“cholesterol, cholesterol ester, phospholipids and fatty acids
Functions of lipoproteins:
Lipoproteins are the transport form of lipids.
1. Chylomicrons: Chylomicrons transport exogenous triglycerides from intestine to
peripheral tissues like adipose tissue and skeletal muscle.
2. VLDL: VLDL transports endogenous triglycerides from liver to extrahepatic tissue
like heart, adipose tissue, muscle, blood vessels etc.
3. LDL: LDL transports cholesterol from liver to extrahepatic tissues
.
4. HDL: HDL transports cholesterol & cholesterol esters from extrahepatic tissue to liver.

38. DEFICIENCIES AND OVERCONSUMPTION
Deficiencies
Deficiency of dietary lipids is very rare because they
are widely distributed in foods.
Deficiency of essential fatty acids and fat soluble
vitamins
Risk includes infants consuming low fat diet
include anorexic nervosa, patients receiving lipid-
free parenteral nutrition for long
periods with malabsorption syndrome.

39. DEFICIENCIES AND OVERCONSUMPTION
Overconsumption
Over consumption of fats is associated with increased risk of
certain chronic diseases,
like, obesity, heart diseases, certain types of cancers etc.
i) Obesity:
Obesity results from a chronic imbalance between energy intake
and energy expenditure.
reasons are;
Fat is more concentrated form of energy than carbohydrates
and proteins.
Obesity can also lead to type II diabetes mellitus and heart
diseases.
Body has the capacity to increase the utilization (oxidation) of
carbohydrate and
protein whenever their intake is high. But, body can not do
so during high fat intak

40. ii)Coronary heart disease:
Development of atherosclerosis and
coronary heart diseases,
Dietary cholesterol increases total and LDL-cholesterol
Poly unsaturated fatty acids lower the levels of total and
LDL-cholesterol and hence
beneficial effect on CHD.
iii) Cancer
High fat diet increase the risk of colon cancer and
breastcancer. They may promote, not cause cancers.