Chapter 5 The Lipids: Fats and Oils. Ask Yourself True or False? 1.The body can store fat in virtually unlimited amounts. 2. Dietary cholesterol is found.

Chapter 5

The Lipids: Fats and Oils

Ask Yourself

True or False?

1. The body can store fat in virtually unlimited amounts.

2. Dietary cholesterol is found only in animal foods.

3. A person’s blood level of cholesterol is a predictor of that person’s risk of having a heart attack.

4. For the health of your heart, the fat you should avoid eating, most of all, is cholesterol.

5. The more monounsaturated fats you consume, the better it is for your health.

Ask Yourself

6. Fruits are essentially fat-free.7. In general, the softest margarines are

the most polyunsaturated.8. Polyunsaturated fat has the same

number of calories as saturated fat.9. All the foods you eat should contain

less than 10% of calories from saturated fat.

10. No one is free of atherosclerosis.

A Primer on Fats

• Lipids: a family of compounds that includes: Triglycerides (fats and oils) Phospholipids (lecithin) Sterols (cholesterol)

• Obvious sources of fat are oil, butter, margarine, and shortening.

• Other foods contributing fat include meat, nuts, mayonnaise, salad dressings, eggs, bacon, gravy, cheese, ice cream, and whole milk.

A Primer on Fats

• Fats Lipids that are

solid at room temperature.

• Oils Lipids that are

liquid at normal room temperature.

Muscles derive fuel from fat.

A Primer on Fats

• After eating, the body stores some fat as an energy reserve.

• The body has unlimited potential to store fat.

• Excess carbohydrate and protein can be converted to fat, but they cannot be made from fat.

• One pound of body fat is worth 3,500 calories.

Within the fat cell, lipid is stored in a droplet. This droplet can enlarge, and the cell membrane will grow to accommodate its swollen contents.

Cell membrane Cell nucleus

Fat droplet

• Satiety The feeling of

fullness or satisfaction that people feel after meals.

Fats slow the rate at which the stomach empties.

A Primer on Fats

A Closer View of Fats

• Excess energy from the energy-yielding nutrients is stored as fat.

• The fat is first broken into fragments called fatty acids.

• Fatty acids Basic units of fat composed of chains of carbon atoms with an acid group at one and and hydrogen atoms attached all along their length.

• Triglycerides The major class of dietary

lipids, including fats and oils.

• A triglyceride is made up of three units known as fatty acids and one unit called glycerol.

• Glycerol An organic compound that

serves as the backbone for triglycerides.

About 95 percent of the lipids in foods and in thehuman body are triglycerides.

A Closer View of Fats

Glycerol + Fatty acids Triglyceride

Fatty acid

Fatty acid

Fatty acid

Glycerol

+

A Closer View of Fats: Other Lipids

•Phospholipid A lipid similar to a triglyceride but containing phosphorus; one of the three main classes of lipids. Examples include:

Lecithin A major constituent of cell membranes,

manufactured by the liver and found in many foods.

•Sterols Lipids with a structure similar to that of cholesterol; one of the three main classes of lipids. Examples include:

Cholesterol One of the sterols, manufactured in the body for a

variety of purposes.

A Closer View of Fats

• Fatty Acids differ in chain length or the number of carbons in a fatty acid.

• Chain length affects solubility.• Fatty acids can be:

Short-chainMedium-chainLong-chain

A Closer View of Fats

• Fatty acids differ in the degree of saturation.

• Saturation refers to the chemical structure—specifically to the number of hydrogens the fatty acid chain holds.Saturated fatty acids are filled to

capacity with hydrogen.Unsaturated fatty acids hold an

“empty spot” or point of unsaturation.

Saturated vs. Unsaturated Fats

• Saturated fatty acid A fatty acid carrying the maximum possible number of

hydrogen atoms (having no points of unsaturation). Saturated fats are found in animal foods like meat, poultry, and full-fat dairy products, and in tropical oils such as palm and coconut.

• Unsaturated fatty acid: a fatty acid with one or more points of unsaturation. Unsaturated fats are found in foods from both plant and animal sources. Unsaturated fatty acids are further divided into monounsaturated fatty acids and polyunsaturated fatty acids.

• Monounsaturated fatty acid: a fatty acid containing one point of unsaturation, found mostly in vegetable oils such as olive, canola, and peanut.

Saturated vs. Unsaturated Fats

Saturated vs. Unsaturated Fats

• Polyunsaturated fatty acid: (sometimes abbreviated PUFA) a fatty acid in which two or more points of unsaturation occur, found in nuts and vegetable oils such as safflower, sunflower, and soybean, and in fatty fish.

Saturated vs. Unsaturated Fats

The Essential Fatty Acids

• The human body can synthesize all fatty acids except:Linoleic acid, linolenic acid Polyunsaturated fatty acids, essential for

human beings.• Essential fatty acid A fatty acid that cannot be synthesized in the

body in amounts sufficient to meet physiological need.

Omega-6 vs. Omega-3 Fatty Acids

• Omega-3 fatty acids, found in fish oils, offer a protective effect on health. Interest in fish oils first

kindled when someone thought to ask why the Eskimos of Greenland, who eat a diet very high in fat, have such a low rate of heart disease.

Blood clot formation, inflammation (e.g. arthritis, asthma), irregular heart rhythm, and cancer also seem to be beneficially affected by DHA and/ or EPA.

Something’s Fishy

Eating fish at least two times per week as part of a balanced diet can:Reduce blood clot formation ( heart

attacks and strokes).Decrease risk of heart arrhythmias. Decrease blood triglycerides.Decrease atherosclerotic plaque formation. Improve health of arteries.Slightly lower blood pressure.

Characteristics of Fats in Foods

The more unsaturated a fat, the more liquid it is at room temperature. The more polyunsaturated the fat is, the sooner it melts.

Characteristics of Fats in Foods

• Unsaturated fats are more likely to react with oxygen and become rancid.

• Food manufacturers may alter fats and oils by: Hydrogenation The process of adding hydrogen to unsaturated fat

to make it more solid and more resistant to chemical change.

Antioxidants A compound that protects other compounds from

oxygen by itself reacting with oxygen. Emulsifiers A substance that mixes with both fat and water

and can break fat globules into small droplets, thereby suspending fat in water.

Other Members of the Lipid Family

Phospholipids… Important components of

cell membranes. Can serve as emulsifiers in

the body, joining with both water and fat.

Also used in foods such as margarine, chocolate, salad dressings, and frozen desserts to keep the fats dispersed.

Widespread in foods.

A Phospholipid: Lecithin

Sterols such as cholesterol• Incorporated as an

integral part of the structure of cell membranes.

• Used to make bile for digestion.

• Used to make sex hormones (estrogen and testosterone).

• Made into vitamin D.• Deposited in the artery

walls, leading to plaque buildup and heart disease.

Sterols such as cholesterolhave a multiple-ringstructure.

Other Members of the Lipid Family

Digestion of fat

Largeintestine

Gallbladder

Liver

MouthSalivaryglands

Stomach

Pancreas

Smallintestine

5. Large intestineSome fat and cholesterol, trapped infiber, are carried out of the body withother wastes.

A. Digestion of Fat1. MouthSome hard fats begin to melt asthey reach body temperature.

2. StomachThe stomach’s churningaction mixes fat with water andacid. A stomach enzymeaccesses and breaks apart asmall amount of fat. Fat is last toleave the stomach.

3. Liver, Gallbladder, andSmall IntestineOnce in the small intestine, fatencounters bile, an emulsifiermade in the liver (see Part B).The gallbladder, a storageorgan, squirts bile into thecontents of the small intestine toblend the fat with the waterydigestive secretions.

4. PancreasFat-digesting enzymes from the pancreas(pancreatic lipase) enter the smallintestine. The enzymes can attack fatonly after emulsification by bile. Theybreak down the triglycerides to fattyacids, glycerol, and monoglycerides.

How the Body Handles Fat

• The products of fat digestion are fatty acids, glycerol, and monoglycerides.Monoglyceride A glycerol molecule with one fatty acid attached

to it. A diglyceride is a glycerol molecule with two fatty acids attached to it.

• The shortest fatty acids and glycerol pass by simple diffusion into the absorptive cells and without further processing can enter the blood stream, travel to the liver, and be converted and used by the body.

How the Body Handles Fat

• Bile A mixture of compounds, including

cholesterol, made by the liver, stored in the gallbladder, and secreted into the small intestine. Bile emulsifies lipids to ready them for enzymatic digestion and helps transport them into the intestinal wall cells.

• Long-chain fatty acids, phospholipids, and cholesterol are insoluble in water and cannot be accepted by the body’s blood and lymph system.Lymph The body fluid that transports the products of fat

digestion toward the heart and eventually drains back into the bloodstream. • Lymph consists of the same components as

blood with the exception of red blood cells.

• These fats must be packaged into one of four types of lipoproteins for transport.

How the Body Handles Fat

• Lipoproteins Clusters of lipids associated with protein that

serve as transport vehicles for lipids in blood and lymph. The four main types of lipoproteins are:

1. Chylomicron A type of lipoprotein that transports newly digested fat

—mostly triglyceride—from the intestine through lymph and blood.

2. VLDL (very-low-density lipoprotein) Carries fats packaged or made by the liver to various

tissues in the body.3. LDL (low-density lipoprotein) Carries cholesterol (much of it synthesized in the liver)

to body cells. A high blood cholesterol level usually reflects high LDL.

4. HDL (high-density lipoprotein) Carries cholesterol in the blood back to the liver for

recycling or disposal.

How the Body Handles Fat

C. Absorption of Fat: The ChylomicronMost of the newly digested fats are absorbed into lymph aspart of a special package—the chylomicron. A chylomicron(lipoprotein) contains an interior of triglycerides andcholesterol surrounded by phospholipids.Proteins cover thestructure. Such anarrangement ofhydrophobic (water-fearing) molecules(the fatty acids) onthe inside andhydrophilic (water-loving)molecules(proteins) on theoutside allows lipidsto travel through thewatery fluids of thebody.

Triglyceride

PhospholipidCholesterolProtein

LDL (derived from VLDL) carriesfats (mostly cholesterol) tobody cells. LDL travelsthrough blood vessels,is vulnerable to attack byoxygen, and has affinity forlinings of artery walls—contributingto plaque buildup.

HDL transportscholesterol frombody cells backto liver for recyclingor disposal.

Body cells

Fat is made available to body cells via enzyme action; afterward, the remnants ofthe chylomicron are returned to the liver.

Chylomicron

Newly digested fatsare transported bychylomicrons.

VLDL makesfats available tobody cells viaenzyme action.

Lipids processed or made inThe liver are released in VLDL.

Remnants ofchylomicronreturn to liver.

A. Functions and Interactions of Lipoproteins

Small intestine

(Cholesterol)

Liver

HDLLDL

VLDL

“Good” vs. “Bad” Cholesterol

• ATHEROSCLEROSIS: As LDL particles penetrate the walls of the arteries, they become oxidized-LDL and next are scavenged by the body’s white blood cells.

• These foam cells are then deposited into the lining of the artery wall.

• This process, known as atherosclerosis, causes plaque deposits to enlarge, artery walls to lose elasticity, and the passage through the artery to narrow.

• Oxidized LDL-cholesterol The cholesterol in LDLs that is attacked by reactive oxygen molecules inside the walls of the arteries. Oxidized LDL is taken up

by scavenger cells and deposited in plaque.

• Foam cells: Cells from the immune

system containing scavenged oxidized LDL-cholesterol that are thought to initiate arterial plaque formation.

“Good” vs. “Bad” Cholesterol

Atherosclerosis

Accumulation of cholesterolloadedfoam cells—plaque formation

White blood cell

White blood cell (scavenger)

Atherosclerosis

Early injury triggersinflammation*

Plaque

Vesselopening

Artery lining

Smooth muscle layer

Normal artery

Oxidized LDL

Muscle cells

LDL +oxygen

Scavenger +oxidized LDL(incorporatedinto liningof artery asCholesterolloaded foamcell)

• Phytochemicals Physiologically

active compounds found in plants that appear to help promote health and reduce risk for cancer, heart disease, and other conditions.

Fats Can Be Healthy

The Mediterranean food pyramid

• Use olive oil and other plant oils that are rich in monounsaturated and polyunsaturated fats.

• Consume more omega-3 fats. Consider eating fish twice a week

as part of a balanced diet. Plant sources of omega-3 fats

include soybeans, flaxseed, pecans, and walnuts.

• Consume a diet that is lower in saturated fat and higher in complex carbohydrates and fiber. Include more fruits, vegetables,

whole-grain breads, and other grains and legumes.

Fats Can Be Healthy

Fat Can Be Healthy

• One place to find omega-3 fats is fish, especially fatty fish like salmon.

• Nuts are rich in many nutrients and other beneficial substances but are also high in fat.

Trans Fatty Acid Controversy

• Trans fatty acid A type of fatty acid created

when an unsaturated fat is hydrogenated.

• Found primarily in margarines, shortenings, commercial frying fats, and baked goods.

• Trans fatty acids have been implicated in research as culprits in heart disease.

Trans Fat Controversy

Margarine

Potato chips, cornchips, popcorn: 5%

Household shortening: 4%

Breakfast cereal: 1%

Animal products

Candy: 1%

Salad dressing: 3%

Fried potatoes: 8%

Cakes, cookies, crackers,pies, bread, etc.

21%

17%

40%

Trans Fat Controversy

In 2006, the Food and Drug Administration began requiring that manufacturers list the trans fat content on food labels.

Compare spreads

Choose Fats Sensibly…• Use nonstick sprays rather than fat

to coat pans. • Try reducing the fat in recipes a

little at a time• Try reducing fat in recipes a little

at a time and use nonstick sprays, fat-free broth or wine in place of butter or margarine.

• Refrigerate soups and broth, then skim off the hardened fat.

• Prepare lean meats, trim visible fats, remove poultry skin and cook meats so that fats can drain off.

• Use herbs, spices, onions or garlic, salsa, lemon juice, or mustard instead of butter, margarine, or oil. Experiment with substitutes.

Bake, broil, poach, or steam.

Season with herbs & spices.

Choose Fats Sensibly

Nourish the Heart

1. Become a savvy supermarket shopper.

2. Keep blood cholesterol at or below the recommended levels.

3. Balance energy intake with energy needs.

• Total fat refers to all the fat in the food: saturated, monounsaturated, polyunsaturated, and trans fat.

• Total fat, saturated fat, trans fat, and cholesterol information are required on the label.

• Listing the amount of monounsaturated and polyunsaturated fats is voluntary.

Checking Out the Food Label for Fat Information

Checking out the food label for fat information

• More than half the people who die in the U.S. each year die of heart and blood vessel disease.

• Twin demons that lead to heart disease are:1. Atherosclerosis: narrowing of the

arteries caused by plaque build-up.2. Hypertension: high blood pressure.

Diet & Heart Disease

A normal artery provides open passage for blood to circulate.

Plaques along an artery wall narrow the passage and obstruct blood flow.

Leading Risk Factors for Heart Disease

• High LDL blood cholesterol level

• Low HDL blood cholesterol level

• High blood pressure• Cigarette smoking• Obesity• Physical inactivity• Diabetes

• An “atherogenic” diet (high in saturated and trans fats, & low in fruits, vegetables, legumes, & whole grains)

• Other risk factors cannot be changed: advanced age, male gender, & family history

Diet and Heart Disease

• Eat a variety of antioxidant-rich fruits and vegetables. Choose nine servings per day.

• Choose fat-free or low-fat dairy products, such as fat-free milk or low-fat or fat-free yogurt. Choose milk or yogurt more often than cheese

• Consume abundant legumes of many varieties, including soybeans, kidney beans, and lentils.

• Eat a variety of whole grains and other foods high in soluble fibers and eat fewer refined grain products.

• Choose soy foods, skinless poultry, lean meat, and fish, especially fish such as salmon that is rich in omega-3 fatty acids, in place of foods high in saturated fat.

• Limit your intake of foods that are high in saturated fat and trans fat, such as full-fat milk products, fatty meats, tropical oils, and partially hydrogenated vegetable oils.

• Limit your intake of foods that are high in calories from solid fats and added sugars, such as cakes, cookies, candy, and ice cream; pizza; cheese; processed and fatty meats; and sweetened beverages.

• Adopt heart-healthy cooking methods, such as broiling, baking, steaming, and stir-frying.

• Reduce daily sodium intake to less than 2,300 milligrams and further reduce intake to 1,500 milligrams if you are 51 or older, African American, or have high blood pressure or diabetes.

• Get more potassium in your diet from foods such as cantaloupe, bananas, beans, and yogurt.

• Consume alcohol only in moderation, if at all. Have no more than one alcoholic drink per day if you’re a woman and no more than two if you’re a man. “One drink” means it has no more than 1⁄2 oz of pure alcohol. Examples of one drink are 12 oz of beer, 5 oz of wine, 11⁄2 oz of 80-proof spirits, or 1 oz of 100-proof spirits.