FATS AND OILS explained in details with illustrations

Fats and oils

1. FATS AND OILS

2. Introduction
•The terminology applied to fats is based on the chemical
structure of their molecules.
• Fats and oils belong to a group of biological substances
called lipids.
•Like all other organic compounds, lipids are composed of a
carbon skeleton with hydrogen and oxygen substitutions.
•Nitrogen, sulphur and phosphorus are also present in some
lipids. Lipids are biological chemicals that do not dissolve in
water.

3. •They serve a variety of functions in organisms, such as
regulatory messengers (hormones), structural components
of membranes, and as energy storehouses.

•Chemists and biochemists use the term ‘lipid’ to describe a
chemically varied group of substances that have in common
the property of being insoluble in water but soluble in
solvents such as chloroform, alcohols and esters.

4. •This definition includes a far wider range of chemical
substances for example glycolipids, sterols, phospholipids,
and the fat soluble vitamins.
•For this lesson, fats will be reserved for the fatty components
of foods and diets. Fats and oils share a common molecular
structure, which is represented by the formula below.

5. •This structural formula shows that fats and oils contain
three ester functional groups.
•Fats and oils are esters of the tri-alcohol, glycerol (or
glycerine).
•Therefore, fats and oils are commonly called triglycerides,
although a more accurate name is triacylglycerols.

6. Saturated and unsaturated fats
•Fatty acids are the basic units of all fats; a fat's physical
characteristics and nutritional activity depend on the kind of
fatty acids it contains.
•A fat is classified as saturated, monounsaturated, or
polyunsaturated according to the type of fatty acids that
occur in the greatest quantity.
•Fatty acids contain an even number of carbon atoms, from 4
to 36, bonded in an unbranched chain.

7. •Most of the bonds between carbon atoms are single bonds.
•If all of these bonds are single bonds, the fatty acid is said to
be saturated, because the number of atoms attached to
each carbon atom is the maximum of four.
•If some of the bonds between carbon atoms are double
bonds, then the fatty acid is unsaturated.

8. •Fats, which are solids are usually more saturated than oils,
which are liquids at room temperature.
•Unlike carbohydrates, lipids are not polymers but rather
small molecules extracted from animal and plant tissues.
•They are a group of compounds characterised by their
insolubility in water and can be classified into six major
groups:

9. Classification of lipids
•Fatty acids-long hydrocarbon chains with carboxylic acid head
groups
•Triglycerides-neutral esters of glycerol and fatty acids
•Phospholipids-ionic esters of glycerol, fatty acids, and phosphate
•Lipids not containing glycerol-sphingolipids, alcohols, waxes, and
steroids
•Lipids combined with other compound-glycolipids and
glycoproteins, usually found in the biomembrane
•Synthetic lipids

10. •Fatty acids are rarely free in nature and almost always linked to
other molecules by their hydrophilic carboxylic acid head group.
•They exist primarily as unbranched hydrocarbon chains with an even
number of carbons variably saturated with hydrogen.
•Fatty acids are classified according to the number carbons in the
chain, the number of double bonds, and the position of the first
double bond.
•Both chain length and saturation contribute to the melting
temperature of a fat. In general, fats with shorter fatty acid chains or
with more double bonds are liquid at room temperature.
Fatty Acids

11. Chain length
•Plants and animals require fatty acids of specific chain length and
saturation for structural and metabolic needs.
•Food sources thus differ with respect to the composition of fatty
acid chain lengths they contain.
•In general, butter and milk fat contain predominantly short chain
fatty acids (SCFA) with 4 to 6 carbons, animals contain long chain
fatty acids with 16-20 carbons

12. Saturation
•In a saturated fatty acid (SFA), all binding sites not linked to carbon
are saturated with hydrogen. No double bond. The most abundant
MFA in human blood is monounsaturated oleic acid.
• Monounsaturated fatty acid (MFA) contains only one double bond
•Polyunsaturated fatty acids (PUFA) contain two or more double
bonds.
•Because fatty acids with double bonds are vulnerable to oxidative
damage, humans and other warm blooded organisms store fat
predominantly as saturated palmitic and stearic fatty acids.

13. Location of double bonds
•Fatty acids are also characterised by the location of the double bonds.
•Two conventions are used to describe the location of the double
bonds.
•Greek capital letter delta (Δ) refers to the carbon preceding the double
bond. E.g. Δ9 refers to the double bond between carbon 9 and 10.
• Alpha (α) refers to the first carbon adjacent to the carboxyl group,
beta (ß) to the second carbon, and omega (ώ) to the last carbon
counted from the terminal methyl carbon.
•Thus arachidonic acid (20:4 ώ6), the major highly polyunsaturated fat
in the membranes of land animals is an omega 6 fatty acid. It has four
double bonds; the first is 6 carbons from the terminal methyl group.

14. Triglycerides
•Triglycerides are formed by joining three fatty acids to a glycerol
side chain.
•Because free fatty acids contain a carboxylic (COOH) acid head
group, fatty acids can react with other molecules and are
potentially dangerous.
•To avoid tissue damage, biologic organisms bind three fatty acids
to glycerol.
•The OH group on each fatty acid is bound to an OH group on
glycerol.

15. •At each site, a molecule of water is released and an ester (-O-)
linkage is formed.
•Fatty acids linked to glycerol are neutral and the triglyceride is
water insoluble (hydrophobic).
•‘Neutral fats’ can be safely transported in the blood and stored
in the fat cell as an energy reserve.

16. Phospholipids
•These are derivatives of phosphatidic acid, a triglyceride
modified to contain a phosphate group at the third position.
•The phosphate containing portion of the molecule is charged and
forms hydrogen bonds with water while the two fatty acids form
hydrophilic interactions with other fatty acids.
•Phospholipids make up more than 50% of the biomembrane lipid
layer and provide a lipid barrier to unregulated transport of
water-soluble molecules into the cell.

17. Visible and invisible fats
•In nutrition and dietetics, a distinction is often made
between visible and invisible fats.
•Visible fats are those clearly apparent to the consumer e.g.
the spreads, the cooking oils and the fat on meats.
•In contrast, a great deal of the fat in many of our foods is
hidden by incorporation during preparation and cooking, for
example in cakes, biscuits and potato crisps, or in
formulation of processed meats and sausages and in
emulsions such as mayonnaise.

18. •Hidden fats may also be present in the membranes of animal
tissue and in plants.
•Hence, the total fat content in the diet is hard to measure,
because different samples of the same food may vary widely
in fat content as well as in fat type, especially for the case of
meat.
Good and bad fats
•Dietary fats serve many functions in the body. Perhaps the
most important is structural – they are the major constituent
of every cell membrane in the body.
•The membrane, or outer lining of a cell, determines what goes
into and out of that cell, like a gatekeeper.
•As such, they are critical in the proper functioning of the cell.

19. •Saturated fats are bad because they are sticky and tend to clump
together, causing problems for cell health.
•Trans fatty acids are bad because their altered shape, as a result of
processing changes their function, causing irregularities in the cell
structure and changing the permeability of the cell membrane.
•Those fats derived from unprocessed, polyunsaturated food sources
are good fats.
•They are more fluid and allow easier and healthier function.
• In fact, there are two families of fats that are not only good, they
are termed essential - meaning that the body cannot make them
and they must be obtained from the diet.

20. •They are the Omega 3 and Omega 6 essential fatty acids
(EFAs).
•These essential fats perform a crucial function by producing
messengers called prostaglandins
•Prostaglandins are hormone-like substances that can be
thought of as "master switches" that regulate and control
almost all cellular activity.
• Examples of their work include controlling inflammation,
blood pressure, and immune system activity.

21. Problem with saturated fats
•To
 understand the problem with eating too much saturated fat, we
must examine its relationship to cholesterol. High levels of
cholesterol in the blood have been linked to the development of
heart disease, strokes, and other health problems.
•Despite its bad reputation, our bodies need cholesterol, which is
used to build cell membranes, to protect nerve fibers, and to
produce vitamin D and some hormones, chemical messengers that
help coordinate the body’s functions. We just do not need
cholesterol in our diet. The liver, and to a lesser extent the small
intestine, manufacture all the cholesterol we require.
•When we eat cholesterol from foods that contain saturated fatty
acids, we increase the level of a cholesterol-carrying substance
(LDLP) in our blood that harms our health.

22. Oxygenation and hydrogenation of fats
•EFAs are very important, but are, unfortunately, fragile and easily
“deactivated.”
• The main processes that alter them are heat, oxygenation, and
hydrogenation.
•Oils are exposed to high heat during processing and cooking.
•Oxygenation, a more subtle process, occurs when the oil is
exposed to air and light, such as when oils sit on grocery shelves.
•Hydrogenation occurs when hydrogen is bubbled through oils, as is
done in the making of margarine. This process extends the shelf
life of the oil, and, as in the case of margarine, turns a liquid
vegetable oil into one that is solid at room temperature.

23. •EFAs go through two detrimental changes when they undergo
the above processes:
•First, they can release what are called free radicals. Think of
free radicals as particles zipping around cells looking to attach
or "link" with just about anything.
•In so doing, they damage the other molecules in the cell and set
off chain reactions producing other free radicals.
•Premature aging, heart disease, cancer, and other degenerative
processes are the result of unbridled free radical activity.

24. •Second, the beneficial natural oils actually change their
molecular configuration or shapes, forming what are termed
trans fatty acids (TFAs).
• These TFAs are biochemically different and are not able to
fulfil the same function as the original oil.
•Unfortunately, they can still take the place of the
biochemically active essential fats in cell membranes,
acting to slow production of the beneficial prostaglandins.
•There is also some evidence to suggest that they may act
like free radicals and promote tissue destruction.

25. Types of fats in the body and their functions
Generally, it is convenient to divide them into structural, storage, and
metabolic fats. It should however be emphasised that there is a
considerable overlap between the different fat types
Structural fats
•These are those that contribute to the architecture of cells, mainly as
constituents of cell membranes. In animal membranes the
phosphoglycerides are the major lipids.
• Phosphoglycerides are mixed acid esters of glycerol with two fatty
acids and one phosphoric acid residue.

26. •Phospholipids are technically called amphiphilic lipids because they
possess groups that associate with water.
Storage fats
•Provide a long term reserve of metabolic fuel for the organism.
•Triglycerides are by far the most important storage form of lipids.
•Storage fats tend to contain a higher proportion of saturated or
monounsaturated fatty acids, although this is only a general
guideline.
•In man, the biggest reservoir of fatty acids to supply the long term
energy is the adipose tissue. Egg yolk lipids provide a store of fuel for
the developing embryo.

27. •Storage fats and structural fats are present in bulk; they fulfil their
specialized functions as a result of their chemical and physical
properties.
•Thus triglycerides are ideal for storage since they have an energy
density over twice that of carbohydrates, and they take up less space
than say, glycogen, as they are not hydrated.
Metabolic fats
•Lipids that, as individual molecules undergo metabolic
transformations to produce a specific substance of physiological and
nutritional importance. Cholesterol is metabolized in the adrenal
gland to a variety of steroid hormones, and in the liver to a variety of
bile acids that are secreted in the bile and are subsequently involved
in the digestion and absorption of dietary diets

28. FATS IN FOODS
•Saturated fatty acids are known to increase and PUFA to decrease,
plasma lipids. However, too much PUFA can be dangerous.
•Double bonds are highly reactive and bind oxygen to form peroxides
when exposed to air or heat.
•Oxidised fats produce the off flavours and odours described as rancidity.
Saturated fat and partially hydrogenated oils have fewer oxygen-binding
sites and thereby have increased stability and longer shelf life.
•PUFA-rich oils are also reactive in cooking. When subjected to routine
frying or cooking practices, PUFA can generate high levels of toxic
products that promote cardiovascular disease. To prevent toxic product
formation, PUFA are often fortified with vitamin E or synthetic
antioxidants such as butylated hydroxyanisole (BHA).

29. WHY DO WE EAT FAT
1. Palatability
•For most people foods are more palatable if they have a
substantial fat content. For the nutritionist or dietitian, this is
not an unimportant matter, since whatever its nutrient
composition may be, food has no nutritive value if it is not
eaten. Fats contribute to palatability in two ways:
•By the response to their texture in the mouth (mouthfeel)
•By the olfactory responses of taste in the mouth and aroma
in the nose

30. 2.As an energy source
Most people think primarily of fats as sources of metabolic energy.
Triglycerides represent a vey concentrated form of fuel.
3. A source of essential nutrients
•Dietary lipids provide two types of essential nutrients: the essential
fatty acids and the fat soluble vitamins
•

31. CHOLESTEROL
•Cholesterol is a
 
waxy,
 fatlike compound that is found throughout
the body.
•Cholesterol is notorious for its role in clogging arteries and thus
contributing to heart disease and stroke. But cholesterol is essential
to the body, too.
• It is an important component in cell membranes, and the body
uses cholesterol in making sex hormones, adrenal hormones, and
vitamin D.
•Chemically, cholesterol is a complex alcohol of a type known as
sterols. It is also a lipid, which means that it does not dissolve in
water.

32. Effects of cholesterol
•A
 close 
relationship
 exists among levels of blood cholesterol in the
body, those of other fats or lipids, and the development of
atherosclerosis (Arteriosclerosis).
•In this disorder, plaques containing cholesterol are deposited on
the walls of arteries, particularly arteries of small and medium size,
reducing their inside diameter and the flow of blood.
• Clotting of blood, such as may occur in the coronary arteries to
cause a heart attack, is most likely to develop at places where
arterial walls are roughened by such plaques.

33. •Because
 
cholesterol
 is insoluble in water
, it cannot be carried
in solution in the blood.
• Instead, it is ferried through the bloodstream as part of a
complex molecule composed of protein and lipid.
•Scientists have identified three forms of cholesterol-carrying
proteins in the blood: high-density lipoproteins (HDL), low-
density lipoproteins (LDL), and very low-density lipoproteins
(VLDL).

34. •LDL and VLDL appear to promote atherosclerosis, and they are
often referred to as “bad cholesterol.” By contrast, HDL appears to
retard atherosclerosis, earning it the nickname of the “good
cholesterol.”
•People
 who are born with a predisposition to have abnormally
high levels of cholesterol—especially LDL and VLDL cholesterol—
can reduce their risk of heart attack by lowering their blood
cholesterol.
•This is done by following a diet low in cholesterol and saturated
fats, getting sufficient exercise, and using certain drugs.

35. •A
 
low
 HDL level
 
also 
increases the risk of heart disease. Researchers
believe that HDL cholesterol carries cholesterol to the liver and
helps prevent the formation of arterial plaques. Thus, raising levels
of HDL, the so-called good cholesterol, may help prevent
atherosclerosis and heart attacks. Regular exercise helps some
people raise their HDL levels. Studies suggest that the B vitamin
niacin can elevate HDL levels.
•Saturated fats are considered harmful to the heart and blood
vessels because they are thought to increase the level of LDLs and
VLDLs and decrease the levels of HDLs.
•Monounsaturated
 fats—found in olive, canola, and peanut oils—
appear to have the best effect on blood cholesterol, decreasing the
level of LDLs and VLDLs

36. FAT INTAKE RECOMMENDANTIONS AND GUIDELINES
•The vast array of fat types in the diet, coupled with the growing realization that
the type of fat consumed may has important consequences in the body, suggests
that recommendations about dietary fat consumption must consider fat type as
well as fat amount. The following guidelines may be essential
Note:
•Fat is an efficient way to pack more calories in less volume and, thus, fat is
important for feeding infants and young children
•After the first year of life, there is no particular advantage in using fat to provide
calories
•However, flavor and texture of foods are highly dependent on their fat content
•

37. •Infants fed breast milk consume 50% fat
•After weaning, they should progressively reach the recommended fat
intake level for adults, by age 8-10
Total fat for adults
•About 20% to 35% of total calories can be derived from fat

38. Summary of fat functions
•Energy storage, mobilization, and utilization
•Prostaglandin, cytokine synthesis
•Cell differentiation and growth
•Cell membrane structure, myelination
•Signal transmission
•Hormone synthesis
•Bile acid synthesis