Chapter 5
Fats: Essential Energy-Supplying Nutrients
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
May be solid or liquid at room temperature.
Three types of lipids are found in foods
 Triglycerides (TG)
 Phospholipids
 Sterols
Triglycerides
Triglycerides are composed of
 Three fatty acid (FA) molecules
 Fatty acids: long chains of carbon atoms surrounded by hydrogen atoms
 One glycerol molecule
 Glycerol: is an alcohol composed of 3-carbon atoms and is the backbone of a
triglyceride
Chain length affects TG function
 Fatty acids can differ in number of carbon they contain
 Chain length determines method of digestion and absorption and how fats
function in the body
 Short-chain FA- <6
 Medium-chain FA- 6–12
 Long-chain- >14
 Level of saturation
 Saturation refers to how many hydrogen atoms surround each carbon; and
every carbon atom is saturated by hydrogen
Saturated fatty acids (SFAs) have no double bonds between carbons
Unsaturated fats contain less hydrogen
 Monounsaturated fatty acids (MUFAs) lack hydrogen atoms in one region;
and one double bond.
 Polyunsaturated fatty acids (PUFAs) lack hydrogen atoms in multiple
locations; and have two or more double bonds.
Note: Each double bond causes the loss of two hydrogen atoms.
 Shape
 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, coconut oil, animal fats, butter, and lard are high in saturated fatty acids
o Unsaturated fatty acids do not stack together well and are liquid at room temperature.
 Unsaturated fatty acids are the predominant type in plants.
 Two exceptions are coconut and palm kernel oil
 The hydrogen atoms at the unsaturated region can be arranged in different positions.
 Cis: has both hydrogen atoms on the same side of the double bond carbon chain
 Trans: has hydrogen atoms attached on opposite sides of the double bond carbon
chain
 Most trans fats are produced by hydrogenation
Hydrogenation: the addition of hydrogen atoms to unsaturated fatty acids.
 Converts liquid fats (oils) into a semi-solid (spreadable) or solid form
 Used to create margarine from plant oil
 Often creates trans fatty acids
 Listed on the food label as partially hydrogenated oil
Triglycerides and Health
Saturated and trans fats are harmful to health.
 Saturated and trans fats lower “good” cholesterol and raise the “bad” cholesterol
 As of January 2006 trans fat content is required on the food label
Fatty Acids and Health
Some triglycerides contain Essential fatty acids
 Two fatty acids cannot be synthesized in the body and must be obtained in the diet are
 Linoleic and alpha-linolenic acid are essential (required in the diet) fatty acids.
 They are converted into important regulatory compounds in the body.
Linoleic acid (omega-6 fatty acid)
 Found in vegetable and nut oils
 Converted by the body to arachidonic acid which is involved in blood clotting and
blood pressure
 Needed for cell membrane structure and lipoproteins
Alpha-linoleic acid (omega-3 fatty acid)
 Found in vegetables, fish and fish oils
 Converted to EPA and DHA which are important regulators of inflammation, blood
clotting and blood pressure
Phospholipids
Phospholipids
 Are composed of
 Glycerol backbone
 Two fatty acids
 Phosphate
 Are soluble in water
 Are manufactured in our bodies so they are not required in our diet
 Important component of cell membranes
Sterols
Sterols: lipids containing multiple rings of carbon atoms.
 Are essential components of cell membranes and many hormones
 Are manufactured in our bodies (in the liver and intestines);
 Are not essential components of our diet
 Cholesterol is the major sterol found in the body and most common sterol in the diet
The Role of Fat
Energy
 Fat is very energy dense, containing 9 kcal/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
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
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
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
 Minimal digestion occurs in the stomach from gastric lipase
Digestion and absorption of fats occurs primarily in the small intestine.
The gallbladder, liver, and pancreas assist in fat Digestion
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 triglycerides into two separate fatty acids and a
monoglyceride
 Fat enters the mucosal cell as a micelle (fatty acids, monoglycerides, phospholipids,
and sterols)
In the intestinal mucosal cell
 Fatty acids are reattached to the monoglyceride to reform triglycerides
 A small amount of protein is added to the lipids forming a chylomicron
 Chylomicron: a lipoprotein produced by cells lining the small intestine
 Composed of triglycerides surrounded by phospholipids and proteins
 Soluble in water
Chylomicrons are the transport vehicle that removes absorbed fats from the small
intestine.
 Travel through the lymphatic system
 Are transferred to the bloodstream
Short- and medium-chain fatty acids are absorbed more quickly since they are not
arranged into chylomicrons.
 Once the chylomicron gets to a cell in the body, the triglycerides in the chylomicrons
must be disassembled by lipoprotein lipase into two fatty acids and a monoglyceride
before they can pass through the cell membrane
 After entering the cell, the two fatty acids and monoglyceride reform a triglyceride
 The triglyceride can be
 Used immediately for energy
 Used to make lipid-containing compounds
 Stored in liver and muscle cells
How Much Fat?
 The Acceptable Macronutrient Distribution Range (AMDR) for fat is 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.
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 (e.g., olive oil) and
polyunsaturated fats (e.g., plant oils)
 Essential fatty acids
 The adequate intake for linoleic acid is 11 to 17 grams per day, or 5 to 10% of
total energy intake
 The adequate intake for alpha-linolenic acid is 1.1 to 1.6 grams per day, or 0.6
to 1.2% of total energy intake
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
Beneficial Fats
Increased consumption of “good” fats is advised
 Increase consumption of omega-3 fatty acids
 Flaxseed oil, fish, canola oil, walnuts
Avoid consumption of contaminated fish
 Mercury, PCB’s levels can be high some fish
Fat Replacers
Many fat replacers have been introduced
 Olestra and other fat replacers have been introduced to help people reduce caloric
intake
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 help protect against cardiovascular disease.
Risk factors for cardiovascular disease include
 Being overweight
 Physical inactivity
 Smoking
 High blood pressure
 Diabetes
 High blood cholesterol
Blood lipids include
 Chylomicrons
 VLDLs—very low-density lipoproteins
 LDLs—low-density lipoproteins
 “bad cholesterol”
 HDLs—high-density lipoproteins
 “good cholesterol”
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)
Trans fatty acids
 Can raise blood cholesterol levels more than 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.