Chapter 5 - Lipids: Triglycerides, Phospholipids, and Sterols

Question 1

Lipids

Answer 1

Fat refers to the class of nutrients known as lipids. The lipid family includes triglycerides (fats and oils), phospholipids, and sterols. Triglycerides are most abundant, both in foods and in the body.

Composed of carbon (C), hydrogen (H), and oxygen (O). Because lipids have many more carbons and hydrogens in proportion to their oxygens, they can supply more energy per gram than carbohydrates

Question 2

Triglycerides

Answer 2

Contains one molecule of glycerol and three fatty acids (basically, chains of carbon atoms).

To make a triglyceride, a series of condensation reactions combine a hydrogen atom (H) from the glycerol and a hydroxyl (OH) group from a fatty acid, forming a molecule of water (H2O) and leaving a bond between the two molecules

Question 3

Glycerols

Answer 3

An alcohol composed of a three-carbon chain, which can serve as the backbone for a triglyceride. condensation: a chemical reaction in which water is released

Question 4

Saturated fatty acid

Answer 4

Fully loaded with all its hydrogen atoms and contains only single bonds between its carbon atoms.

Question 5

Length of carbon chain

Answer 5

Most naturally occurring fatty acids contain even numbers of carbons in their chains—up to 24 carbons in length.

The 18-carbon fatty acids, which are abundant in our food supply. Stearic acid is the simplest of the 18-carbon fatty acids

The long-chain (12 to 24 carbons) fatty acids of meats, seafood, and vegetable oils are most common in the diet. Smaller amounts of medium-chain (6 to 10 carbons) and shortchain (fewer than 6 carbons) fatty acids also occur, primarily in dairy

Question 6

The number of double bonds

Answer 6

The double bond is a point of unsaturation.

Single double bond - unsaturated fatty acid

two or more carbon to carbon double bonds - polyunsaturated fatty acid

Question 7

Monosaturated Fats

Answer 7

fatty acids that have one double bond in the fatty acid chain with all of the remainder carbon atoms being single-bonded

Question 8

Fatty acids

Answer 8

A chain of carbon and hydrogen atoms with an acid group (COOH) at one end and a methyl group (CH3) at the other end.

Differ from one another, however, in the length of their carbon chains and in the number and location of their double bonds,

May be 4 to 24 (even numbers of) carbons long, the 18-carbon ones being the most common in foods and especially noteworthy in nutrition.

Fatty acids may be saturated or unsaturated. Unsaturated fatty acids may have one or more points of unsaturation—that is, they may be monounsaturated or polyunsaturated.

Of special importance in nutrition are the polyunsaturated fatty acids known as omega-3 fatty acids and omega-6 fatty acids.

The 18-carbon polyunsaturated fatty acids are linolenic acid (omega-3) and linoleic acid (omega-6). Both are essential fatty acids that the body cannot make. Each is the primary member of a family of longer-chain fatty acids that help to regulate blood pressure, blood clotting, and other body functions important to health.

Question 9

Linoleic fatty acid

Answer 9

18-carbon fatty acid common in vegetable oils, lacks four hydrogens and has two double bonds.

essential fatty acid

Question 10

Linolenic fatty acid

Answer 10

A fourth 18-carbon fatty acid with three double bonds.

essential fatty acid

Question 11

Location of the double bond

Answer 11

Chemists identify polyunsaturated fatty acids by the position of the double bond closest to the methyl (CH3) end of the carbon chain, which is described by an omega number.

A polyunsaturated fatty acid with its closest double bond three carbons away from the methyl end is an omega-3 fatty acid.

An omega-6 fatty acid is a polyunsaturated fatty acid with its closest double bond six carbons away from the methyl end.

Question 12

Firmness

Answer 12

The degree of unsaturation influenced the firmness of fats at room temp.

Generally, most polyunsaturated fatty acids (vegetable oil) are liquid at room temperature, and the more saturated animal fats are solid.

Generally, the shorter the carbon chain, the softer the fat is at room temperature.

Question 13

Antioxidants

Answer 13

As a food additive, preservatives that delay or prevent rancidity of fats in foods and other damage to food caused by oxygen

Question 14

Stability

Answer 14

The degree of unsaturation also influences stability.

All fats become spoiled when exposed to oxygen. The oxidation of fats produces a variety of compounds that smell and taste rancid.

Polyunsaturated fats spoil most readily because their double bonds are unstable; monounsaturated fats are slightly less susceptible. Saturated fats are most resistant to oxidation

Question 15

Monounsaturated fatty acid

Answer 15

Tend to belong to the omega-9 group, with their closest (and only) double bond nine carbons away from the methyl end. Oleic acid—the 18 carbon monounsaturated fatty acid common in olive oil mentioned earlier—is an omega-9 fatty acid.

Question 16

Protect fats from spoilage

Answer 16

Manufacturers do 3 things:

1. products may be sealed in air-tight, nonmetallic containers, protected from light, and refrigerated—an expensive and inconvenient storage system.
2. manufacturers may add antioxidants to compete for the oxygen and thus protect the oil
3. products may undergo a process known as hydrogenation.

Question 17

Hydrogenation

Answer 17

Some or all of the points of unsaturation are saturated by adding hydrogen molecules.

Total hydrogenation rarely occurs during food processing. Most often, a fat is partially hydrogenated, and some of the double bonds that remain after processing change their configuration from cis to trans

Question 18

cis

Answer 18

On the near side of; refers to a chemical configuration in which the hydrogen atoms are located on the same side of a double bond.

most occurring in nature

Question 19

trans

Answer 19

On the other side of; refers to a chemical configuration in which the hydrogen atoms are located on opposite sides of a double bond.

Question 20

Trans-fatty acids

Answer 20

Fatty acids with hydrogens on opposite sides of the double bond.

Only a few fatty acids (notably a small percentage of those found in milk and meat products)

Behave more like saturated fats, increasing blood cholesterol and the risk of heart disease

Question 21

Conjugated linoleic acids

Answer 21

naturally occurring trans fatty acids

several fatty acids that have the same chemical formula as linoleic acid (18 carbons, two double bonds) but with different configurations (the double bonds occur on adjacent carbons).

Question 22

Phospholipids

Answer 22

Make up only 5 percent of the lipids in the diet.

Whitney, Eleanor Noss; Rolfes, Sharon Rady. Understanding Nutrition (p. 136). Cengage Textbook. Kindle Edition.

Best known is lecithin - one glycerol with two of its three attachment sites occupied by fatty acids like those in triglycerides. The third site is occupied by a phosphate group and a molecule of choline.

The hydrophobic fatty acids make phospholipids soluble in fat; the hydrophilic phosphate group allows them to dissolve in water.

Such versatility enables the food industry to use phospholipids as emulsifiers to mix fats with water in such products as mayonnaise, salad dressings, and candy bars

Found naturally in eggs, liver, soybeans, wheat gern and peanuts

Constituents of cell membranes

Question 23

Sterols

Answer 23

Compounds with a multiple-ring structure. The most famous sterol is cholesterol.

Foods derived from both plants and animals contain sterols, but only those from animals contain significant amounts of cholesterol—meats, eggs, seafood, poultry, and dairy products.

Plant sterols interfere with cholesterol absorption. By inhibiting cholesterol absorption, a diet rich in plant sterols lowers blood cholesterol levels.

Question 24

Roles of sterols

Answer 24

Many vitally important body compounds are sterols.

Among them are bile acids, the sex hormones (such as testosterone), the adrenal hormones (such as cortisol), and vitamin D, as well as cholesterol itself.

Cholesterol in the body can serve as the starting material for the synthesis of these compounds or as a structural component of cell membranes; more than 90 percent of all the body’s cholesterol is found in the cells.

Despite popular impressions, cholesterol is not a villain lurking in some evil foods—it is a compound the body makes and uses.

The chemical structure is the same, but cholesterol that is made in the body is called endogenous, whereas cholesterol from outside the body (from foods) is called exogenous

Question 25

Plaque

Answer 25

Cholesterol’s harmful effects in the body occur when it accumulates in the artery walls.

These plaque deposits lead to atherosclerosis, a disease that causes heart attacks and strokes.

Question 26

Lipid digestion

Answer 26

The goal of fat digestion is to dismantle triglycerides into small molecules that the body can absorb and use—namely, monoglycerides, fatty acids, and glycerol.

Question 27

In the mouth - lipid digestion

Answer 27

Fat digestion starts off slowly in the mouth, with some hard fats beginning to melt when they reach body temperature.

A salivary gland at the base of the tongue releases an enzyme (lingual lipase) that plays an active role in fat digestion in infants, but a relatively minor role in adults.

Question 28

Stomach - lipid digestion

Answer 28

This churning grinds the solid pieces to finer particles, mixes the chyme and disperses the fat into small droplets.

These actions help to expose the fat for attack by the gastric lipase enzyme— an enzyme that performs best in the acidic environment of the stomach.

Still, little fat digestion takes place in the stomach;

Question 29

Small intestine - lipid digestion

Answer 29

Most of the hydrolysis of triglycerides occurs in the small intestine.

When fat enters the small intestine, it triggers the release of the hormone cholecystokinin (CCK), which signals the gallbladder to release its stores of bile.

Among bile’s many ingredients are bile acids, which are made in the liver from cholesterol and have a similar structure.

In addition, bile acids often pair up with an amino acid (a building block of protein). The amino acid end is hydrophilic, and the sterol end is hydrophobic. This structure enables bile to act as an emulsifier, drawing fat molecules into the surrounding watery fluids. There, the fats are fully digested as they encounter lipase enzymes from the pancreas and small intestine.

The major fat-digesting enzymes are pancreatic lipases; some intestinal lipases are also active. These enzymes remove each of a triglyceride’s outer fatty acids one at a
time, leaving a monoglyceride.

Question 30

Phospholipids and sterol digestion

Answer 30

Phospholipids are digested similar to lipids —that is, their fatty acids are removed by hydrolysis. The two fatty acids and the remaining glycerol and phosphate fragments are then absorbed.

Most sterols can be absorbed as is; if any fatty acids are attached, they are first hydrolyzed off.

Question 31

Factors that lower LDL and/or raise HDL

Answer 31

• Weight control
• Monounsaturated or polyunsaturated, instead of saturated, fat in the diet
• Soluble dietary fibers
• Phytochemicals
• Moderate alcohol consumption
• Physical activity

Question 32

VLDL (Very-Low-Density Lipoproteins)

Answer 32

The type of lipoprotein made primarily by liver cells to transport lipids to various tissues in the body; composed primarily of triglycerides.

The lipids made in the liver and those collected from chylomicron remnants are packaged with proteins as VLDL

As the VLDL travel through the body, cells remove triglycerides. As they lose triglycerides, the VLDL shrink and the proportion of lipids shifts.

Cholesterol becomes the predominant lipid, and the lipoprotein becomes smaller and more dense. As this occurs, the VLDL becomes an LDL (low-density lipoprotein), loaded with cholesterol, but containing relatively few triglycerides.

Question 33

Bile

Answer 33

Make lipids accessible to the fat-digesting lipases that dismantle triglycerides

After bile enters the small intestine and emulsifies fat, it has two possible destinations.

Most of the bile is reabsorbed from the small intestine and recycled.

The other possibility is that some of the bile can be trapped by dietary fibers in the large intestine and excreted.

Because cholesterol is needed to make bile, the excretion of bile effectively reduces blood cholesterol.

The dietary fibers most effective at lowering blood cholesterol this way are the soluble fibers commonly found in fruits, whole grains, and legumes.

Question 34

Lipid Absorption

Answer 34

Small molecules (glycerol and short- and medium-chain fatty acids) can diffuse easily into the intestinal cells; they are absorbed directly into the bloodstream.

Larger molecules (monoglycerides and long-chain fatty acids) are emulsified by bile, forming spherical complexes known as micelles.

The micelles diffuse into the intestinal cells where the monoglycerides and long-chain fatty acids are reassembled into new triglycerides.

Within the intestinal cells, the newly made triglycerides and other lipids (cholesterol and phospholipids) are packed with protein into transport vehicles known as chylomicrons.

The intestinal cells then release the chylomicrons into the lymphatic system.

The blood carries these lipids to the rest of the body for immediate use or storage.

Question 34

Chylomicrons

Answer 34

Lipid packages with protein escorts for transport so that the cells all over the body may select needed lipids from them.

Are the largest and least dense of the lipoproteins. They transport diet-derived lipids (mostly triglycerides) from the small intestine (via the lymph system) to the rest of the body.

Cells all over the body remove triglycerides from the chylomicrons as they pass by, so the chylomicrons get smaller and smaller.

Within 14 hours after absorption, most of the triglycerides have been depleted, and only a few remnants of protein, cholesterol, and phospholipid remain.

Question 36

HDL (High-Density Lipoproteins)

Answer 36

The liver makes HDL (high-density lipoprotein) to remove cholesterol from the cells and carry it back to the liver for recycling or disposal.

By efficiently clearing cholesterol, HDL lowers the risk of heart disease.

In addition, HDL have anti-inflammatory properties that seem to keep artery-clogging plaque from breaking apart and causing heart attacks.

Question 37

LDL (Low-Density Lipoproteins)

Answer 37

Linked most directly to heart disease

LDL circulates throughout the body, making their contents available to the cells of all tissues—muscles (including the heart muscle), fat stores, the mammary glands, and others.

The cells take triglycerides, cholesterol, and phospholipids to use for energy, make hormones or other compounds, or build new membranes.

Special LDL receptors on the liver cells play a crucial role in the control of blood cholesterol concentrations by removing LDL from circulation.

Question 37

Lecithen

Answer 37

One of the phospholipids. Both nature and the food industry use lecithin as an emulsifier to combine water-soluble and fat-soluble ingredients that do not ordinarily mix, such as water and oil

Question 39

Lipids provide

Answer 39

Fat stores provide energy - twice that of carbs and protein
Insulate against temp
Protect against shock
Maintain cell membranes

Question 39

Adipokines

Answer 39

The hormone that adipose tissue secretes. It is a protein that helps regulate energy balance and influences several body functions.

When body fat is markedly reduced or excessive, the type and quantity of adipokine secretions change, with consequences for the body’s health.

Obesity, for example, increases the release of the adipokine resistin that promotes inflammation and insulin resistance—factors that predict heart disease and diabetes.

Question 40

Lipoproteins

Answer 40

Transport lipids around the body. All four types of lipoproteins carry all classes of lipids (triglycerides, phospholipids, and cholesterol), but the chylomicrons are the largest and contain mostly triglycerides from the diet;

VLDL are smaller and are about half triglycerides

LDL are smaller still and contains mostly cholesterol

HDL are the densest and are rich in protein.

High LDL cholesterol indicates an increased risk of heart disease, whereas high HDL cholesterol has a protective effect.

Question 42

Adipose tissue

Answer 42

The body’s fat tissue; consists of masses of triglyceride-storing cells.

More than just a storage depot for fat. Adipose tissue actively secretes several hormones known as adipokines

The body’s fat stores have virtually unlimited capacity, thanks to the special cells of the adipose tissue.

Adipose tissue actively secretes several hormones known as adipokines—proteins that help regulate energy balance and influence several body functions. When body fat is markedly reduced or excessive, the type and quantity of adipokine secretions change, with consequences for the body’s health.

Question 43

Essential Fatty Acids

Answer 43

The human body needs fatty acids, and it can make all but two of them—linoleic acid (the 18-carbon omega-6 fatty acid) and linolenic acid (the 18-carbon omega-3 fatty acid).

These two fatty acids must be supplied by the diet notably, from vegetable oils, seeds, nuts, fish, and seafood.

Question 44

Arachidonic

Answer 44

An omega-6 polyunsaturated fatty acid with 20 carbons and four double bonds; present in small amounts in meat and other animal products and synthesized in the body from linoleic acid.

Question 45

Emulsifier

Answer 45

Substances with both water-soluble and fat-soluble portions that promotes the mixing of oils and fats in watery solutions.

Question 46

Lipids role in the body

Answer 46

Lipids provide energy, insulate against temperature extremes, protect against shock, and maintain cell membranes.

Fat provides more than twice the energy of carbohydrate and protein, ♦ making it an extremely efficient storage form of energy.

Question 47

Linoleic Acid and the Omega-6 Family

Answer 47

Linoleic acid is the primary member of the omega-6 fatty acid family. When the body receives linoleic acid from the diet, it can make other members of the omega-6 family—such as the 20-carbon polyunsaturated fatty acid, arachidonic acid.

Question 48

Conditionally essential nutrient

Answer 48

A nonessential nutrient (such as arachidonic acid) that must be supplied by the diet in special circumstances.

Question 49

Linolenic Acid and the Omega-3 Family

Answer 49

Primary member of the omega-3 fatty acid family.* Like linoleic acid, linolenic acid cannot be made in the body and must be supplied by foods. Given the 18-carbon linolenic acid, the body can make small amounts of the 20- and 22-carbon members of the omega-3 family, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA),

Question 50

Eicosanoids

Answer 50

Diverse group of compounds that are sometimes described as “hormonelike,”

Differ from hormones in important ways.

1. Hormones are secreted in one location and travel to affect cells all over the body, whereas eicosanoids appear to affect only the cells in which they are made or nearby cells
2. They have different effects on different cells.

Question 51

Omega-6 fatty acids

Answer 51

Protect heart health by lowering LDL cholesterol and improving insulin

Question 52

Storing Fat as Fat

Answer 52

After meals, the blood delivers chylomicrons and VLDL loaded with triglycerides to the adipose cells for storage.

An enzyme—lipoprotein lipase (LPL)—hydrolyzes triglycerides from these lipoproteins, releasing fatty acids, diglycerides, and monoglycerides into the adipose cells.

Question 53

Using Fat for Energy

Answer 53

Fat supplies about 60 percent of the body’s ongoing energy needs during rest. During prolonged light to moderately intense exercise or extended periods of food deprivation, fat stores may make a slightly greater contribution to energy needs.

During energy deprivation, several lipase enzymes (most notably hormonesensitive lipase) inside the adipose cells respond by dismantling stored triglycerides and releasing the glycerol and fatty acids directly into the blood.

Question 54

Blood lipid profile

Answer 54

Reveals the concentrations of various lipids in the blood, notably triglycerides and cholesterol, and their lipoprotein carriers (VLDL, LDL, and HDL). This information alerts people to possible disease risks and perhaps to a need for changing their physical activity and eating habits.

Question 55

Heart Disease

Answer 55

Much of the effort to prevent heart disease focuses on lowering LDL cholesterol.

Saturated fats are most often implicated in raising LDL cholesterol.

Most notable among the saturated fatty acids that raise blood cholesterol are lauric, myristic, and palmitic acids (12, 14, and 16 carbons, respectively).

In contrast, stearic acid (18 carbons) seems to have little or no effect on blood cholesterol.17

Question 56

Cancer

Answer 56

The links between dietary fats and cancer are not as evident as they are for heart disease. Dietary fat does not seem to initiate cancer development but, instead, may promote cancer once it has arisen.

Stronger risk factors for cancer include smoking, alcohol, and environmental contaminants.

Question 57

Recommended Intakes of Saturated Fat, Trans Fat, and Cholesterol

Answer 57

The DRI and Dietary Guidelines suggest a diet that provides 20 to 35 percent of the daily energy intake from fat.

Less than 10 percent of daily energy intake from saturated fat, as little trans fat as possible, and less than 300 milligrams cholesterol.

Question 58

Beneficial effects of the omega-3 polyunsaturated fatty acids.

Answer 58

helps to prevent blood clots, protect against irregular heartbeats, improve blood lipids, and lower blood pressure, especially in people with hypertension or atherosclerosis.

In addition, omega-3 fatty acids support a healthy immune system and suppress inflammation.

May protect against some cancers as well, perhaps by suppressing inflammation.

Question 59

Recommended Intakes of Monounsaturated and Polyunsaturated Fats

Answer 59

The 20 to 35 percent of kcalories from fat recommendation provides for the essential fatty acids—linoleic acid and linolenic acid—and Adequate Intakes (AI) have been established for these two fatty acids.

The DRI suggests that linoleic acid provides 5 to 10% of the daily energy intake and linolenic acid 0.6 to 1.2%