Ch 4 ppt

CHAPTER 4

Lipids

Eleanor D. Schlenker

Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc.

2 Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc.

Health Issues and Lipids

Health concerns related to dietary fat

generally focus on two issues:

1. The high-energy intake associated with a diet high

in fat

2. The negative health effects of saturated and trans

fatty acids


Health Issues and Lipids – Cont’d

Amount of Fat

Fat contains 9 kcal/g versus 4 kcal/g (protein

and carbohydrates)

High-fat intakes may supply excess kcalories,

stored in adipose tissue

Inappropriate increases in body fat are

associated with type 2 diabetes,

hypertension, and heart disease


Health Issues and Lipids – Cont’d

Type of Fat

High intakes of saturated fats and cholesterol

promote atherosclerosis, the buildup of fatty deposits

on the interior walls of the major arteries that

increase risk of heart attack or stroke

Saturated fat is found primarily in animal sources;

cholesterol is found only in animal sources

Unsaturated fats can decrease risk of cardiovascular

disease

Trans fats, produced in commercial processing of

lipids, are deleterious to health


Lipids in Nutrition and Health

Food Lipids

Lipids found in food carry out important body

functions

Provide fuel for energy

• Food lipids yield 9 kcalories (kcal)/g

Supply essential fatty acids

• Linoleic acid and alpha-linolenic acid


Lipids in Nutrition and Health –

Cont’d

Food Lipids – cont’d

Lipids found in food carry out important body

functions – cont’d

Support absorption of the fat-soluble vitamins

Add to food palatability

Promote satiety



Cont’d

Roles in the Body

Storage source of energy

Fatty acids are the preferred fuel of the heart

muscle

Thermal insulation to assist in temperature

regulation

Protection of vital organs from damage



Cont’d

Roles in the Body – cont’d

Transmission of nerve impulses

Form membrane structure

Carrier of fat-soluble materials

Lipoproteins

Fat-soluble vitamins A,D, E, and K

Precursors of other substances


The Physical and Chemical

Nature of Lipids

Physical Characteristics

Lipid: Fats, oils, and related compounds that

are insoluble in water and greasy to the touch

Hidden fat: Foods that may appear to be

mainly carbohydrates (bakery items) or

protein (beef patty) often contain significant

amounts of fat



Nature of Lipids – Cont’d

Chemical Characteristics

Lipids are organic compounds consisting of a

carbon chain as a “backbone,” with hydrogen

and oxygen atoms and other radicals or

groups of elements attached



Nature of Lipids – Cont’d

Chemical Characteristics – cont’d

Carbohydrates and lipids have two important

differences:

1. Lipids are more complex in structure, with more

carbon (C) and hydrogen (H) atoms and fewer

oxygen (O) atoms

2. The common structural units of lipids are fatty

acids, whereas the common structural units of

carbohydrates are simple sugars


Characteristics of the Fatty Acids:

Saturation

Saturated lipids are hard, less saturated are

soft, and unsaturated are liquid at room

temperature

Fatty acids that have some hydrogen spaces

unfilled are less saturated



Saturation – Cont’d

Saturated Fats

Food lipids are composed of saturated fatty

acids

Examples: coconut oil, approximately 88%

saturated; palm kernel oil, approximately 80%

saturated

Milk fats and meat fats are high in saturated

fatty acids




Monounsaturated

Food lipids made up of fatty acids with one

hydrogen space unfilled, creating one double

bond

Examples: canola oil and olive oil




Polyunsaturated

Fatty acids that have two or more spaces

unfilled with hydrogen, creating two or more

double bonds

Examples: corn oil and safflower seed oil

n-3 fatty acids in fatty fish are beneficial for

cardiovascular health

n-6 fatty acids, e.g., linoleic acid


Characteristics of Fatty Acids:

Chain Length

Chain length ranges from 4 carbons to 22

carbons

Chain length affects absorption

Long-chain fatty acids are more difficult to absorb

and require a helping carrier

Short- and medium-chain fatty acids are soluble in

water and can be absorbed directly into the

bloodstream

MCT oil may be used in intestinal diseases


Essential Fatty Acids

Two essential fatty acids for humans:

1. Linoleic acid (n-6)

2. Alpha-linolenic acid (n-3)

Arachidonic acid, a fatty acid important in

human nutrition, can be made from linoleic

acid

Eicosapentaenoic acid and docosahexaenoic

acid can be made from alpha-linolenic acid


Essential Fatty Acids – Cont’d

Linoleic acid and alpha-linolenic acid have

various roles in the body:

Skin integrity

Blood cholesterol regulation

Growth


Essential Fatty Acids – Cont’d

Linoleic acid and alpha-linolenic acid have

various roles in the body – cont’d

Gene expression

Immune function

Blood platelet aggregation

Synthesis of hormone-like agents


Dietary Reference Intakes

Adequate Intake (AI) for linoleic acid (an n-6

fatty acid):

17 g/day for men ages 19 to 50 years

12 g/day for women ages 19 to 50 years

14 g/day for men age 51 and older

11 g/day for women age 51 and older


Dietary Reference Intakes –

Cont’d

AI for alpha-linolenic acid (an n-3 fatty acid):

1.6 g/day for all adult men

1.1 g/day for all adult women


Dietary Reference Intakes –

Cont’d

Special needs of infants

Arachidonic acid and docosahexaenoic acid play a

critical role in infant development

Liberal amounts are found in breast milk

Commercial infant formula is now fortified with

these fatty acids

Pregnant and lactating women are encouraged to

eat 1-2 portions of fatty sea fish per week


Food Sources

Best source of linoleic and alpha-linolenic

acids:

Vegetable oils

Best sources of linoleic acid:

Corn oil, safflower oil, soybean oil, cottonseed oil,

sunflower oil, and peanut oil

Best sources of alpha-linoleic acid:

Canola oil, soy oil, linseed oil, rapeseed oil, and

dark green leafy vegetables


Food Sources – Cont’d

Eicosapentaenoic and docosahexaenoic acids

are obtained from fish

Can be made from alpha-linoleic acid

Recommend two servings of fish per week

Vegans or others who do not eat fish may use

fortified foods and fatty-acid-rich algae

High intakes may lead to excessive bleeding and

interfere with other fatty acid metabolism

Foods are always the best sources


Triglycerides

Fatty acids are stored in the body in the form

of triglycerides


Triglycerides – Cont’d

Triglycerides are made of three fatty acids

attached to a glycerol base

Glycerides contain glycerol and fatty acids

• Monoglyceride: glycerol is combined with one fatty acid

• Diglyceride: with two fatty acids

• Triglyceride: with three fatty acids


Degree of Saturation

Food lipids contain both saturated and

unsaturated fats

Foods from animal sources—such as meat,

milk, and eggs—contain more saturated fats


Degree of Saturation – Cont’d

Most food lipids from plant sources, primarily

vegetable oils, are unsaturated but there are

exceptions:

Coconut oil and palm kernel oil are among the

most saturated fats occurring naturally in foods


Degree of Saturation – Cont’d

The nutrition label can guide a consumer's

choice of fats

Indicates the number of grams of total fat,

saturated fat, unsaturated fat, and trans fat per

serving

Importance of considering serving sizes

Foods free of trans fats are not necessarily healthy


Cis Versus Trans Fats

Hydrogenation changes unsaturated liquid

oils into solid fats such as margarine and

shortening


Cis Versus Trans Fats – Cont’d

When oils are partially hydrogenated to

produce more solid fats, the normal bend can

change such that the two structural parts are

on opposite sides of the bend

This form is called a trans fatty acid, meaning

“opposite side”


Cis Versus Trans Fats – Cont’d

Trans fatty acids are found in breads, cakes,

cookies, crackers, margarine, and frozen

potato products

Trans fatty acids decrease high-density

lipoprotein (HDL) cholesterol levels and

increase low-density lipoprotein (LDL)

cholesterol levels


Visible and Hidden Fat

Visible Fat

Butter, margarine, vegetable oil, salad dressing,

bacon, etc.

Hidden Fat

Milk (except nonfat), egg yolk, cheese, nuts,

seeds, olives, bakery items, frozen entrees

Meat and poultry contain visible and hidden fat


Appropriate Intakes of Fat and

Carbohydrates

Acceptable Macronutrient Distribution Range

(AMDR) for fat:

20% to 35% of total kcalories

Keep saturated fat less than 10% of total

calories


Appropriate Intakes of Fat and

Carbohydrates – Cont’d

AMDR for carbohydrates:

45% to 65% of total kcalories

Low carbohydrate diets may contain >45% of

kcalories as fat

Fat intakes below 10% of energy intake may

not supply sufficient essential fatty acids


Health Promotion

Fast-food restaurants add to fat intake

On days with a fast-food meal, men and women

obtain 34.9% and 34.6%, respectively, of their

total kcalories from fat

On days when all meals are eaten at home or at

food outlets other than the fast-food variety, fat

supplies only 33.6% and 32.7% of total kcalories

in men and women, respectively.


Health Promotion – Cont’d

Lowering Fat Intake

Substituting a modified-fat food for a higher-

fat food

Limiting portion sizes of higher-fat foods to

reduce both fat and kcalories

Choosing a food preparation method that

limits or eliminates fat


Fat Replacers

Food technologists have developed fat

replacers for use in processed foods

In the United States, 79% of consumers buy

foods containing fat replacers


Fat Replacers – Cont’d

Ingredients that can fulfill the functional role

of fats in recipes but are lower in kcalories

than fat

Most are carbohydrates—plant

polysaccharides, celluloses, or gums

Most act as thickeners and emulsifiers


Fat Replacers – Cont’d

Olestra interferes with absorption of fat-

soluble vitamins, so these are added to

olestra-containing products

Certain fat replacers are not digested and

remain in the stomach longer; they may add

to satiety and assist in appetite control

Most (but not all) add fewer kcalories than

would fat


Lipid-Related Compounds

Cholesterol

Belongs to a family of substances called

steroids and travels in the blood attached to

long-chain fatty acids (as cholesterol esters)


Lipid-Related Compounds –

Cont’d

Cholesterol – cont’d

Functions

Required for normal body function and can be

synthesized in the liver

Precursor to steroid hormones

Formation of bile acids

Component of brain and nerve tissue

Component of cell membranes


Cholesterol

Cholesterol occurs naturally in animal foods

but not plant foods

Food sources containing cholesterol:

Egg yolk, meat, whole milk, and cheese

Liver and organ meats

Animal fats (but not plant fats)


Cholesterol – Cont’d

Suggested Cholesterol Intake

The American Heart Association

recommends that dietary cholesterol be held

to 300 mg/day or less

Intake averages about 358 mg in men and

237 mg in women

Certain plant sterols interfere with absorption


Lipoproteins

Function

The liver serves as the body's clearing house

for fatty acids and cholesterol whether

obtained from the diet or produced or

released from body tissues


Lipoproteins – Cont’d

Function – cont’d

When received by the liver, fatty acids and

cholesterol are:

Packaged into lipoproteins

Released into the circulation for transport to cells


Lipid Transport

Lipids are insoluble in water and therefore insoluble in water-based blood

The body produces lipoproteins, packages of lipids wrapped in water-soluble protein


Lipid Transport – Cont’d

Phospholipids are molecules in which one of the three fatty acids attached to a glycerol base is replaced with a water-soluble phosphate (PO4

-3) group


Lipid Transport – Cont’d

Phospholipids in cell membranes help lipid

molecules move from the circulatory system

into the cell

The lipoproteins with their attached

apolipoprotein serve as the major vehicle for

lipid transport in the blood


Classes of Lipoproteins

Lipoproteins are classified according to their

density

Five lipoprotein classes are:

Chylomicrons

Very low-density lipoproteins (VLDLs)

Intermediate density lipoproteins (IDLs)

Low-density lipoproteins (LDLs)

High-density lipoproteins (HDLs)


Cholesterol, Lipoproteins, and

Cardiovascular Risk

LDLs

Transport cholesterol from the liver to the tissues

Elevated LDLs promote atherosclerosis

Cause buildup of fatty plaque in blood vessels

HDLs

Return cholesterol from the cells to the liver for

excretion

Slow or prevent the progression of atherosclerosis

and lower cardiovascular risk


Digestion-Absorption-Metabolism

Digestion

Triglycerides are broken down into individual

fatty acids for absorption

Mouth

No chemical breakdown of lipids



– Cont’d Stomach

Gastric lipase (tributyrinase) acts on

emulsified butterfat

General peristalsis continues the mechanical

mixing of lipids with the stomach contents



– Cont’d Small Intestine

Digestive secretions for lipid breakdown

come from three sources:

1. Bile from the liver and gallbladder: cholecystokinin

(CCK) triggers its release

2. Enzymes from the pancreas: pancreatic lipase

and cholesterol esterase

3. Enzyme from the small intestine: lecithinase


Absorption

Lipid absorption is complicated

Transporting lipids from the small intestine into the

bloodstream takes place in three stages:

• Stage I: Initial lipid absorption (micellar bile-lipid

complex)

• Stage II: Absorption within the intestinal wall (enteric

lipase digestion and triglyceride synthesis)

• Stage III: Final absorption and transport (chylomicrons

and lipoprotein lipase) via the portal blood

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