Chapter 5 - Fats taught by Norman D. Sossong, MD, PhD NSCC – NTR150 – Spring 2008.

Chapter 5 - Fats

taught by

Norman D. Sossong, MD, PhD

NSCC – NTR150 – Spring 2008

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

What Are Fats?

Fats are one type of lipid.

Lipids: diverse class of molecules that are insoluble in water.

Lipids (fats) do not dissolve in water.

Lipids

Description:

• A nonpolar, organic molecule

• Fatlike

• Insoluble in water

• Dissolve readily in nonpolar organic solvents

Lipid Types

Fats

Oils

Waxes

Steroids

Phospholipids

Carotenoids


What Are Fats?

Three types of lipids are found in foods:

• Triglycerides

• Phospholipids

• Sterols

Lipids: Fats = Triglycerides

Composed of:

• Glycerol

• Fatty acids

Ratio of H:O > 2:1


Triglycerides

Triglycerides are composed of

• Three fatty acid molecules• Fatty acids are long chains of carbon atoms

surrounded by hydrogen atoms

• One glycerol molecule• Glycerol is a 3-carbon alcohol that is the backbone

of a triglyceride


Triglycerides

Glycerol

A 3-carbon alcohol

One hydroxyl group on each carbon

Glycerol + 3 Fatty Acids → Triglyceride

Fatty acids

Long hydrocarbon chains ending in a carboxyl (-COOH) group

•Typical length is 14 to 20 carbon atoms


Fatty Acids in Triglycerides

Fatty acids can differ in

• Length of their carbon chain

• Level of saturation

• Shape

Fatty Acids Differ in Length

Chain Length• 4-24 carbons

•Typical length;• 14-24 carbon

atoms

Short-, medium-, or long-chain


Fatty Acids in Triglycerides



• Level of saturation• Saturation refers to how many hydrogen atoms

surround each carbon

• Shape

3 Types of Fatty acids

Saturated

Unsaturated

Polyunsaturated

Fatty acids

Saturated

• All the internal carbon atoms have single bonds with either C or H• This represents the maximum amount of H atoms that

can be attached

• (Animal fats are typically saturated)

Saturated F

at

Fatty acids: Levels of Saturation

Saturated

Unsaturated

• One, or more, of the carbons are attached with 2 or 3 bonds• Bend at the double bonds

• (Most plant fats are unsaturated;• Palm & coconut oils are notable exceptions)

Un

saturated

Fat

Polyunsaturated Fat

Polyunsaturated

• There are 2 or more double bonds• Bend at the double bonds →

• Low melting points

• Usually liquid at room temperatures = oil

Fatty Acids: Level of Saturation

Degree of saturation

• Saturated

• All single bonds between carbons

• Monounsaturated

• One carbon-carbon double bond

• Polyunsaturated

• More than one carbon-carbon double bond


Physical Properties• Saturated Fats

• Tend to be solids at room temperature

• Unsaturated Fats• Tend to be liquids at room temperature

Applications & Sources• Saturated Fats

• Tend to be structurally useful in land animals

• Unsaturated Fats• Tend to be found in cold-water fish & plants


Triglycerides



• Level of saturation

• Shape


Triglycerides

The shape of a triglyceride is determined by the saturation of the carbon chains.

Saturated fatty acids can pack tightly together and are solid at room temperature.

• For example animal fats, butter, and lard are high in saturated fatty acids.


Triglycerides

Saturated fatty acids have hydrogen atoms surrounding every carbon in the chain.

Monounsaturated fatty acids lack hydrogen atoms in only one region.

Polyunsaturated fatty acids lack hydrogen atoms in multiple locations.


Triglycerides


Triglycerides

Unsaturated fatty acids do not stack together well and are liquid at room temperature.

• Plant oils have unsaturated fatty acids.

The hydrogen atoms at the unsaturated region can be arranged in different positions:

• Cis – same side of the carbon chain

• Trans – opposite sides of the chain

Fatty acids

Saturated

Unsaturated

Polyunsaturated

Cis- vs. trans- fatty acids


Triglycerides

Fatty Acids Are Key Building Blocks

Types of fatty acids

• Cis and trans• Hydrogenation produces trans fatty acids


Triglycerides

Hydrogenation: The addition of hydrogen atoms to unsaturated fatty acids.

• Coverts liquid fats (oils) into a more solid form

• Used to create margarine from plant oil

• Often creates trans fatty acids

Fatty Acids Are Key Building Blocks

Types of fatty acids

• Cis and trans• Hydrogenation produces trans fatty acids

• Essential fatty acids• Linoleic acid and alpha-linolenic acid

• Can’t be made in the body

• Used to make eicosanoids

Triglycerides = Fats

Structure

• Glycerol + 3 fatty acids

Functions

• Energy source and reserve

• Insulation and protection

• Carrier of fat-soluble vitamins

• Sensory qualities in food


Used to store energy in organism

• 9 kilocalories (kcal)/gram• [compared with 4 kcal/gram for carbohydrates]

• Saturated fats tend to have more energy than unsaturated fats• 2 C-H vs. 1 C=C

• → animal fats usually have more calories than do vegetable fats

Triglycerides in Food

Sources of omega-3 fatty acids

• Soybean, canola, walnut, flaxseed oils

• Salmon, tuna, mackerel

Sources of omega-6 fatty acids

• Vegetable oils

• Nuts and seeds

Photos © PhotoDisc


What Are Fats?


• Triglycerides

• Phospholipids

• Sterols


Phospholipids

• Are composed of

• Glycerol backbone

• 2 fatty acids

• Phosphate


Phospholipids

• Are composed of

• Glycerol backbone

• 2 fatty acids

• Phosphate

Phospholipids

Modified fats

• = a triglyceride with one fatty acid chain replaced by a phosphate-containing group

Phospholipids

Composed of

• Polar “head” (phosphate group) at one end

• 2 nonpolar “tails” at the other end

Phospholipids

Composed of

• Polar “head” (phosphate group) at one end

• 2 nonpolar “tails” at the other end


Phospholipids

• Form bilipid layers which form biological membranes


Phospholipids

• Are soluble in water

• Are manufactured in our bodies; so they are not required in our

diet

Phospholipids: Summary

Structure• Glycerol + 2 fatty acids +

phosphate group

Functions• Component of cell membranes• Lipid transport as part of

lipoproteins• Emulsifiers

Food sources• Egg yolks, liver, soybeans, peanuts


What Are Fats?


• Triglycerides

• Phospholipids

• Sterols


Sterols

Sterols: Lipids containing multiple rings of carbon atoms.

• Are essential components of cell membranes and many hormones

• Are manufactured in our bodies and therefore are not essential components of our diet


Sterols

Cholesterol

Cholesterol

Sterols: Cholesterol

Functions• Component of cell membranes• Precursor to other substances

• Sterol hormones• Vitamin D• Bile acids

Synthesis• Made in the liver• From saturated fats

Food sources• Found only in animal foods

Steroids

Composed of 4 carbon rings

Examples

• Cholesterol

• Estrogen

• Progesterone

• Aldosterone

• Testosterone

Lipid and L

ipid-Related M

olecules


Digestion of Fats

Fats are not digested and absorbed easily because they are insoluble in water.

No digestion of fats occurs in the watery environments of the mouth or stomach.

Digestion of fats begins in the small intestine.


Digestion of Fats

As fat enters the small intestine

• Bile is secreted from the gall bladder into the small intestine

• Bile is produced by the liver and stored in the gall bladder

• Bile disperses fat into smaller fat droplets

• Pancreatic enzymes break fat into 2 separate fatty acids and a monoglyceride


Digestion of Fats

Digestion and Absorption

Mouth and stomach

• Minimal digestion of triglycerides

Small intestine

• Emulsified by phospholipids

• Digested by pancreatic lipase

• Absorbed into intestinal cells• Formed into chylomicrons and moved into

lymphatic system


Digestion of Fats

Fatty acids are arranged as lipoproteins for absorption and transport.

Chylomicron: A lipoprotein produced by cells lining the small intestine.

• Composed of fatty acids surrounded by phospholipids and proteins

• Soluble in water


Structure of a Lipoprotein


Digestion of Fats

Chylomicrons are absorbed by cells of the small intestine, then

• Travel through the lymphatic system

• Transferred to the bloodstream

Short- and medium-chain fatty acids are absorbed more quickly since they are not arranged into chylomicrons.


Digestion of Fats

Triglycerides in the chylomicrons must be disassembled by lipoprotein lipase before they can enter body cells.

After entering body cells, triglycerides can be

• Used immediately for energy

• Used to make lipid-containing compounds

• Stored in liver and muscle cells

Cholesterol Transport in Blood

Lipoproteins

• Chylomicrons

• VLDL = Very Low Density Lipoproteins

• LDL = Low Density Lipoproteins

• HDL = High Density Lipoproteins

Lipids in the Body

Lipoproteins carry lipids around the body

• Chylomicrons• Delivers dietary lipids from

intestines to cells and liver

Lipids in the Body

Very-low-density lipoproteins (VLDL)• Deliver triglycerides to cells

Low-density lipoproteins (LDL)• Deliver cholesterol to cells

High-density lipoproteins (HDL)• Pick up cholesterol for removal or recycling

Lipoprotein Composition


The Role of Fat

Energy

• Fat is very energy dense, containing 9 kcal per gram.

• Much of the energy used during rest comes from fat.

• Fat is used for energy during exercise, especially after glycogen is depleted.

• Fat is also used for energy storage.


The Role of Fat

Essential fatty acids

• Two fatty acids cannot be synthesized in the body and must be obtained in the diet

• Alpha-linoleic acid (omega-3 fatty acid)

• Found in vegetables, fish and fish oils

• Linoleic acid (omega-6 fatty acid)

• Found in vegetable and nut oils


The Role of Fat

Fat-soluble vitamins

• Vitamins A, D, E, and K are soluble in fat; fat is required for their transport

Fat is essential to many body functions

• Cell membrane structure

• Nerve cell transmissions

• Protection of internal organs

• Insulation to retain body heat


The Role of Fats

Fat provides flavor and texture to foods.

Fat contributes to making us feel satiated because

• Fats are more energy dense than carbohydrates or protein

• Fats take longer to digest


How Much Fat?

The Acceptable Macronutrient Distribution Range (AMDR) for fat:

20-35% of calories should be from fat

Athletes and highly active people may need more energy from carbohydrates and can reduce their fat intake to 20-25% of total calories.


How Much Fat?

The type of fat consumed is important.

• Saturated fat should be no more than 7% of total calories.

• Trans fatty acids should be reduced to the absolute minimum.

• Most fat in our diets should be from monounsaturated fats (eg., olive oil).


Food Sources of Fat

Visible fats

• Fats we knowingly add to foods

• Butter, cream, mayonnaise, dressings

Invisible fats

• Fats hidden in foods

• Naturally occurring or added during processing

Lipids in the Diet

Recommended intake• Reduce saturated and trans fat intake

• Saturated fats → ↑ cholesterol production• Trans fat → ↑ risk of heart attacks

• Total fat: 20-35% of calories• Need ~ 2% of calories as essential fatty

acids• Improve balance of

omega-3: omega-6 fatty acids

Photos © PhotoDisc

What are sources of highly saturated fats?

Animal products such as:• Lard

• Pork

• Beef

• Lamb

• Chicken fat

• Butterfat• Cream

• Butter

• Cheese

(Note: fish oil is not very saturated)

What are sources of highly saturated fats?

Vegetable products such as:• Coconut oil

• Palm oil

• Chocolate

Note: both coconut oil and palm oil are widely used in prepared foods such as:

• Cakes

• Puddings

• Frozen dinners

Unsaturated Fats

Are oils at Room Temperatures

Help reduce cholesterol in the blood

Types:

• Monounsaturated

• Polyunsaturated

Monounsaturated Fat Sources

Olive oil

Canola oil

Peanut oil

Almonds

Avacados

Cashews

Polyunsaturated Fat Sources

Corn oil

Soybean oil

Safflower oil

Sunflower oil

Cottonseed oil

Sesame oil

Walnuts

Cholesterol Sources

Not made by plants

Animal kingdom

• Humans• Liver

• Saturated fats the amount made

• Foods of animal origin

Foods of Animal Origin That Act as Cholesterol Sources

Shell fish

Meats

Poultry

Egg yolks (but not egg whites)

Cream (and products made from cream)

• Butter

• Cheese

• Ice cream

Lipids and Health

Obesity

• High fat diets promote weight gain

Heart disease

• High saturated and trans fat intake raises LDL cholesterol

Cancer


Health Problems From Fat

Cardiovascular disease

• Dysfunction of the heart or blood vessels

• Can result in heart attack or stroke

The type of fat in our diet can contribute to or protect against cardiovascular disease.


Cardiovascular Disease

Risk factors for cardiovascular disease include

• Being overweight

• Physical inactivity

• Smoking

• High blood pressure

• Diabetes



Blood lipids include

• Chylomicrons

• VLDLs – very low-density lipoproteins

• LDLs – low-density lipoproteins• “bad cholesterol”

• HDLs – high-density lipoproteins• “good cholesterol”


Types of Blood Lipids



Diets high in saturated fats

• Decrease the removal of LDLs from the blood

• Contribute to the formation of plaques that can block arteries

• Increase triglyceride levels (chylomicrons and VLDLs)



Cross-section of (a) a normal artery and (b) a partially blocked artery.



Trans fatty acids:

• Can raise blood cholesterol levels as much as saturated fat

• Are abundant in hydrogenated vegetable oils (margarine, vegetable oil spreads)

• Should be reduced to the absolute minimum



How can fat intake protect against heart disease?

Diets high in omega-3 fatty acids (along with moderate exercise) can increase HDL “good” cholesterol levels.

Lipids in the Diet

Fat substitutes

• Different types of composition

• Olestra• Sucrose + fatty acids

• Indigestible – provides zero kcals

• Reduces absorption of fat-soluble vitamins

Chapter 5 - Fats taught by Norman D. Sossong, MD, PhD NSCC – NTR150 – Spring 2008.

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