chapter 5 lipids: fats and oils. the art of nutritional cooking, 3 rd edition baskette/painter ©...

Chapter 5Lipids: Fats and Oils

The Art of Nutritional Cooking, 3rd editionBaskette/Painter

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

All Rights Reserved.2

Key Concepts Fat varies in function and structure. Saturated fat comes largely from animal sources;

unsaturated fat from plants. Saturated fat increases and poly- and monounsaturated

fat decrease low-density lipoprotein (LDL) cholesterol. Omega-3 and omega-6 fatty acids require balanced

consumption. Fat is an necessary component of the diet. Consuming excess saturated fat is a risk factor for

certain diseases. When partially hydrogenating unsaturated fat, trans-fats

are formed. A diet low in saturated fat, free from trans-fat and

moderate in total fat is desirable. Cholesterol serves a vital function in body processes

and in health.




Lipids

Lipid is the umbrella term for the group of substances in foods that are insoluble in water

Dietary lipids are composed of: cholesterol, fats, oils phospholipids




Fats

Fat is a broad term that has many meanings

Butter and lard are fat, Nuts are high in fat, Some meats are fatty, Avocados and olives are high in fat Not all dietary fats are of equal nutritional

value




Fat or Oil

If a lipid is solid at room temperature it is normally called a fat;

If liquid at room temperature it is called an oil




Triglyeride

Most dietary fats and oils are consumed in the form of triglyceride,

a glycerol with three fatty acid chains of various lengths




Fat Saturations

Fatty acid chains can be saturated, monounsaturated, or polyunsaturated

the degree of saturation is determined by the amount of hydrogen on the carbon chain




Saturated Fats

Saturated fat has all of the hydrogen it can possibly hold

it is saturated, or full, with hydrogen for cooking purposes this increases the melting

point; making the fat solid at room temperature




Monounsaturated Fats

Monounsaturated fat is missing one hydrogen pair,

its carbon chain is not saturated indicated by a double bond in its chemical

structure

Liquid at room temperature




Polyunsaturated Fats

Polyunsaturated fatty acids are also not saturated and have more than one double bond

higher numbers of double bonds equals a greater degree of polyunsaturation

Further classified by where the first double bond is located

if the first double bond is on the third carbon from the omega end it is called an omega-3 fat;

if the first bond is on the sixth carbon it is an omega-6 fat




Omega-6

Omega-6 fatty acids are linoleic acid and arachidonic acid

found in plant oils, such as corn, safflower and sunflower




Omega-3

Omega-3 fatty acids are typically found in fish as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)

also found in plants in the form of alpha-linolenic acid (ALA)

found in abundance in flax seed oil and in lesser amounts in walnuts, soy and canola oil




Saturated Fats in the Diet

Most saturated fat in the diet comes from animal products and processed foods

vary in structure and function vary in length and exhibit different

properties lauric and myristic acids are shorter chain

saturated fats that produce the greatest rise in LDL cholesterol in the blood

Not all saturated fats elevate blood cholesterol to the same extent




Plant Based Saturated Fats

Tropical oils such as coconut, palm and palm kernel oils are highly saturated




Healthy Fats

Polyunsaturated fatty acids, such as linoleic acid, lower LDL cholesterol levels and are essential in the diet

The US national nutrition policy has focused on substituting some of the saturated fat in the diet with polyunsaturated fat

consuming a healthy balance of the omega-6 and omega-3 fatty acids is important




Healthy Omega-3

Researchers first found that omega-3 fatty acids might decrease the risk of cardiovascular disease (CVD) in 1971 when the rate of CVD in a Danish population was compared to a group of Eskimos

the Eskimos had a very low incidence of cardiovascular disease yet their diet was very high in animal fat

the fat in the diet was mainly coming from fish, whales and seals, all high in omega-3 fatty acids




Plant Sources of Omega-3 Flax seed oil is the most abundant plant source

with omega-3 totaling about two-thirds of its total oil content

Canola oil, which is made from rapeseed (a relative of the mustard family grown in Canada and the northwestern United States, with oil-rich seeds), contains 60% oleic, 24% linoleic, and 10% alpha-linolenic fatty acid

Walnuts are a good source of alpha-linolenic fatty acid

Soybean oil also contains alpha-linolenic fatty acid, in addition to generous amounts of linoleic acid




Monounsaturated Fats

The main monounsaturated fatty acid is oleic acid,

found in many fats the body produces oleic from acetic acid animal fats vary in oleic acid content from

20 to 40% vegetable oils range from 12 to 75% oleic the richest source of oleic acid is olive oil,

followed by canola oil and then peanut oil




Cholesterol

One of the substances found in plaque that produces atherosclerosis

A fat-like, waxy substance that yields few calories compared to fats

Classified as a sterol and made by the liver

Obtaining it from the diet is unnecessary




Foods High in Dietary Cholesterol

Fish eggs (such as caviar and shad roe),

Brains, Liver, Egg yolks, Shrimp Sardines Milk contains a

small amount of cholesterol, most of it in butterfat

Foods made with large amounts of fat from dairy, such as cheeses and ice cream

All meats, poultry, and fish regardless of how lean they may be

No plants




Cholesterol is Made in the Body

The liver makes much more cholesterol (approximately 1000 milligrams per day) than the body gets from food




Benefits of Cholesterol

Necessary for hormone production,

For vitamin D synthesis,

For making bile the liver produces about 700 milligrams of

cholesterol daily for this purpose alone bile functions as an emulsifier in fat digestion

Also found in human breast milk demonstrating cholesterol’s importance in infant

development




Lecithin

A phospholipid similar to triglycerides but one of the fatty

acids has been replaced by a phosphate group

The most important phospholipid is Lecithin

used in food products as an emulsifier




Digestion of Fat

Begins in the mouth by chewing and mechanically breaking down food

a slight amount enzymatic digestion happens in the mouth by the action of lingual lipase

and in the stomach via gastric lipase

Most fat digestion takes place in the small intestine




Metabolism of Lipids After processing by the liver, individual dietary

fats enter a distribution system in the body our bodies are water based, which normally does not

mix with fats

Triglycerides and cholesterol are then packaged by the liver into lipoproteins that carry them throughout the body

As they are transferred to the body cells lipoprotein shrinks and becomes low density lipoprotein (LDL)




Cholesterol: Good or Bad

There is only one type of cholesterol

When cholesterol is found in food it is neither good nor bad

where it is found in the human body determines if it is good or bad




Fats Needed for Health

Provides energy while excess finds itself stored as body fat

Necessary for transporting fat soluble vitamins

Necessary for insulating the body against the cold

Adds taste and a feeling of fullness




Dietary Recommendations Dietary Reference Intakes (DRI)

recommend that 20 to 35 percent of calories come from fat

in a ratio of about 10 to 1 omega-6 to omega-3

Adequate Intake (AI) for healthy men is: 17 g omega-6 [linoleic acid (LA)] and 1.6 g

omega-3 [alpha linolenic acid (ALA)] per day; 12 g LA, and 1.1 g ALA per day for women the Western diet contains a ratio of omega-6

to omega-3 closer to 20-30 to 1




Hydrogenation of Oils

The process of adding hydrogen to the double bonds of unsaturated fats by using heat and metal catalysts

Changes the cooking and baking qualities margarine, which is partially hydrogenated to allow

vegetable oil to gain the spreading consistency of butter

shortening where liquid oil is changed into a semisolid giving the product a higher melting point

Enhances storage qualities making them last longer on the shelf

Causes some health concern




The Problem with Hydrogenation The process of hydrogenation forms trans-fats, a

byproduct that does not act in the same manner as normal fatty acids, which occur in the cis form

if the hydrogen atoms are on the same side of the carbon chain at the double bond, the arrangement is called cis and the fat molecule is bent

with the trans-fat the hydrogen molecules are on the opposite side of the double bond and the molecule is straightened out and looks like saturated fat

The body perceives the new trans-fat more like saturated fat than unsaturated fat, and thus, it also raises LDL cholesterol levels in the blood




Oxidation of Fats

Fats may spoil in the presence of oxygen

rancidity is the technical term to what happens to fat when oxidation occurs




Commercial Fat Replacers Simplese contains 1 to 2 calories per gram compared to 9 calories

per gram for regular fat Simplese is made from microparticulated protein and is derived

from egg whites or skim milk useful in salad dressings and ice cream inappropriate for cooking

Olestra has no calories made with sugar and a chemically altered fat that passes

unabsorbed through the digestive system also carries out the fat soluble vitamins A, E, D, and K and

enhances their likelihood of excretion ingestion of too much Olestra can cause diarrhea lends itself to frying and is used in potato chip production

The brand name Olean on food packaging signifies the product was made with salatrin, a third substitute for fat

Salatrin contains 5 calories per gram and is only partially absorbed

used in commercial baked goods

Z-trim is one of the most recent fat substitute to hit the market




END

chapter 5 lipids: fats and oils. the art of nutritional cooking, 3 rd edition baskette/painter ©...

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