Nutrition; Fifth Edition; Chapter 5; Lipids
Very Low-Density Lipoproteins (VLDL)
the triglyceride-rich lipoproteins formed in the liver. This enters the bloodstream and is gradually acted upon by lipoprotein lipase, releasing triglyceride to body cells
Lipoprotein
a substance that consists of an LDL "bad cholesterol" part plus a protein, whose exact function is currently unknown
Cholesterol
a waxy lipid (sterol) whose chemical structure contains multiple hydrocarbon rings
Elongation
addition of carbon atoms to fatty acids to lengthen them into new fatty acids
Lipophobic
adverse to fat solvents; insoluble in fat and fat solvents
_____ is an essential omega-3 fatty acid that contains 18 carbon atoms and 3 carbon-carbon double bonds.
alphpa-linolenic acid (ALA)
Glycerol
an alcohol that contains three carbon atoms, each of which has an attached hydroxyl (-OH) group; it forms the backbone of mono-, di-, and triglycerides
_____ are also referred to as intestinal cells.
enterocytes
_____ are fatty acids that the body needs but cannot synthesize and must be obtained from the diet.
essential fatty acids
_____ is a chemical combination of an organic acid and an alcohol.
ester
Adipocytes
fat cells
_____ are compounds that imitate the functional and sensory properties of fats, but contain less available energy than fats.
fat replacers
Visceral Fat
fat stores that cushion body organs
Subcutaneous Fat
fat stores under the skin
_____ are compounds containing a long hydrocarbon chain with a carboxyl group (-COOH) at one end and a methyl group (-CH3) at the other end.
fatty acids
Nonessential Fatty Acids
fatty acids that your body can make when they are needed. It is not necessary to consume them in the diet
A triglyceride is an ester of three fatty acids and _____.
glycerol
_____ is the backbone of mono-, di-, and triglycerides; alone, it is a thick, smooth liquid.
glycerol
Olestra
a fat replacer made from a sucrose backbone with six to eight fatty acids attached. The fatty acid arrangement prevents breakdown by the digestive enzyme lipase, so the fatty acids are not absorbed. It can withstand heat and is stable at frying temperatures. Its trade name is Olean
Essential Fatty Acids
the fatty acids that the body needs but cannot synthesize, and which must be obtained from the diet
Intermediate-Density Lipoproteins (IDL)
the lipoproteins formed when lipoprotein lipase strips some of the triglycerides from VLDL; containing about 40% triglycerides, this type of lipoprotein is more-dense than VLDL and less dense than LDL; also called a VLDL remnant
Saturated Fatty Acid
a fatty acid completely filled by hydrogen, with all carbons in the chain linked by single bonds
Monounsaturated Fatty Acid (MUFA)
a fatty acid in which the carbon chain contains one double bond
Unsaturated Fatty Acids
a fatty acid in which the carbon chain contains one or more double bonds
Polyunsaturated Fatty Acid (PUFA)
a fatty acid in which the carbon chain contains two or more double bonds
Chylomicron
a large lipoprotein particle formed in intestinal cells following the absorption of dietary fats; a chylomicron has a central core of triglycerides and cholesterol surrounded by phospholipids and proteins
Lipoprotein Lipase
the major enzyme responsible for the hydrolysis of plasma triglycerides
Chain Length
the number of carbons that a fatty acid contains; foods containing fatty acids with chain lengths of 4 to 24 carbons, and most have an even number of carbons
Monoglycerides
a molecule of glycerol combined with one fatty acid
Choline
a nitrogen-containing compound that is part of phosphatidylcholinem a phospholipid; choline is also part of the neurotransmitter acetylcholine; the body synthesizes choline from the amino acid methionine
Conjugated Linolenic Acid (CLA)
a polyunsaturated fatty acid in which the position of the double bonds has moved so that a single bond alternates with two double bonds
_____ is the insertion of double bonds into fatty acids to change them into newer fatty acids.
desaturation
List the many functions of triglycerides.
(1) energy source (9 kilocalories per gram), (2) energy reserve (triglycerides in fat cells), (3) insulation and protection (visceral and subcutaneous fat), (4) carrier of fat-soluble compounds, and (5) contribute sensory qualities to foods.
What percentage of energy comes from a serving of potato chips that contains 10 grams of fat and 150 total kilocalories?
60%
KEY CONCEPT 9
Current recommendations suggest eating 20 to 35 percent of calories from fat, while keeping saturated fat, trans fat, and cholesterol intake as low as possible. Over the years, Americans have reduced their percentage of calories from fat, but are eating more total calories and, as a result, more grams of fat. This is in spite of the increased availability of a wide variety of fat substitutes and lower-fat foods. Excessive fat intake has been linked to obesity, heart disease, and cancer.
KEY CONCEPT 7
Digestion breaks down most lipids into glycol, free fatty acids, monoglycerides, and, in the case of phospholipids, a nitrogenous compound. In the small intestine, long-chain fatty acids and monoglycerides are absorbed primarily into the lymphatic system. Glycerol, short-chain fatty acids, and medium-chain fatty acids are absorbed directly into the blood stream. Sterols are mostly unchanged by digestion, and their absorption is relatively poor.
High cholesterol can be a serious threat to health; however, severely low cholesterol can also signal danger in the body. Name three illnesses that may be present along with low cholesterol.
Hemorrhagic stroke, which occurs when a blood vessel ruptures and bleeds into the brain. Such strokes are more likely in individuals with low cholesterol levels because blood with small amounts of cholesterol does not clot as easily. Hypothyroidism, abnormally low activity of the thyroid gland, resulting in retardation of growth and mental development in children and adults. Anemia, a condition marked by a deficiency of red blood cells or of hemoglobin in the blood, resulting in pallor and weariness. Liver disease, any one of a group of disorders of the liver. Tangier disease, a familial disorder characterized by a deficiency of high-density lipoproteins in the blood serum, with storage of cholesteryl esters in tissues.
How much energy from fat will a person receive from eating a serving of potato chips that contains 10 grams of fat?
If a serving of potato chips (about 20 chips) has 10 grams of fat, 90 calories are from fat. That's 10 grams x 9 calories per gram.
Why do health professionals often recommend eating foods rich in soluble fiber to lower blood cholesterol?
It enhances excretion of bile leading to increased cholesterol turnover.
Describe the difference between LDL and HDL in terms of cholesterol and protein composition.
LDL contains a high percentage of cholesterol (which makes its density low), while HDL contains a high percentage of protein (making it a higher density).
Name the two essential fatty acids.
Linoleic acid and alpha-linolenic acid
KEY CONCEPT 8
Lipoprotein carriers transport lipids in the blood. Chylomicrons, formed in the intestinal mucosal cells, transports lipids from the digestive tract into circulation. VLDL carries lipids from the liver to the other body tissues, delivering triglycerides and gradually becoming IDL. The liver takes up IDL and assembled LDL, the main carrier of cholesterol. High blood levels of LDL cholesterol, the "bad cholesterol," have been shown to be a risk factor for heart disease. Circulating HDL picks up cholesterol and sends it back to the liver for recycling or excretion. A relatively high level of HDL cholesterol, the "good cholesterol," reduces risk for heart disease.
What foods contain cholesterol?
Only foods from animal sources contain cholesterol. Organ meats such as brain and liver contain very high levels. Other sources are egg yolks, meats, and dairy products.
KEY CONCEPT 5
Phospholipids are diglycerides (glycerol plus two fatty acids) with a molecule containing a phosphate-nitrogen group attached at the third attachment point of glycerol. This structure gives the phospholipid both hydrophobic and hydrophilic regions, contributing to its functional properties. Phospholipids are major components of cell membranes and act as emulsifiers. They also store fatty acids for release into the cell and serve as a source of choline. Phospholipids are not needed in the diet because the body can synthesize them.
Explain why fat-free foods are not always lower in calories than regular food.
Reducing the amount of fat and saturated fat that you eat is one easy way to limit your overall calorie intake. However, eating fat-free or reduced-fat foods isn't always the answer to weight loss. This is especially true when you eat more of the reduced-fat food than you would of the regular item.
KEY CONCEPT 6
Sterols are hydrocarbons with a distinctive ring structure. Cholesterol is the best-known sterol; other sterols are hormones or hormone precursors. Cholesterol is an important precursor compound and a key component of cell membranes. High levels of blood cholesterol increase the risk of heart disease. Cholesterol is found only in foods of animal origin. Because the body can make all it needs, cholesterol is not a dietary essential.
What does the hardness or softness of a triglyceride typically signify?
The fat's saturation. Typically, the harder a fat is at room temperature, the more saturated it is. Conversely, the softer a fat is at room temperature, the less saturated it is.
The AHA's guidelines focus on overall eating patterns rather than specific percentages of dietary fat. What are the four main goals of the new guidelines?
The newest heart disease and stroke prevention guidelines for doctors urge them to help you avoid heart disease and stroke by prescribing drugs called statins for some of you, treating obesity as a disease, and giving you other resources to stay healthy. The new guidelines focus on the very important areas of: cholesterol, lifestyle, obesity, and risk assessment.
What are the positive and negative consequences of hydrogenating a fat?
The positive consequences of hydrogenation include a longer shelf life (protects against oxidation) and an improved texture for the food containing the hydrogenated lipid. The main negative consequence of hydrogenation is that it makes a fat more saturated, and partial hydrogenation creates trans fatty acids. This makes the fat less healthful.
KEY CONCEPT 1
The term lipid refers to a group of organic molecules, including triglycerides, phospholipids, and sterols, that are soluble in organic solvents and less soluble in water. Fatty acids are key structural components of both triglycerides and phospholipids and are sometimes attached to cholesterol. Fatty acids are carbon chains of varying lengths. Those with no double bond between carbon atoms are called saturated, whereas those with at least one double bond are called unsaturated.
List the recommendations for intake of total fat, saturated fat, and cholesterol.
Total fat: 20-35% of kilocalories, Saturated fat: less than 10% of kilocalories, and Cholesterol: less than 300 milligrams per day
KEY CONCEPT 3
Triglycerides are formed when a glycol molecule combines with three fatty acids. Dietary triglycerides add texture and flavor to food and are a concentrated source of calories. The body stores excess calories as adipose tissue. While storing energy, adipose tissue also insulates the body and cushions its organs. The fat in food carry valuable fat-soluble nutrients into the body and help with their absorption.
KEY CONCEPT 4
Triglycerides are found mainly in foods we think of as fats and oils, but also in nuts, seeds, meats, and dairy products. Saturated fatty acids are found mainly in animal foods and tropical oils, whereas polyunsaturated fatty acids are found in vegetable oils and other plant foods. Unsaturated fatty acids are susceptible to spoilage by oxidation. Hydrogenation of oils protects fats from oxidation but creates trans fatty acids, which increase risk for heart disease.
What is the most common form of lipid found in food?
Triglycerides. Triglycerides contain a glycerol molecule and 3 fatty acids. These fatty acids can vary in length and saturation.
KEY CONCEPT 2
Unsaturated fatty acids can have cis or trans double bonds. The body can make many of the fatty acids it needs, but cannot make linoleic or alpha-linoleic acids, so these are dietary essentials. The body can elongate and desaturate essential fatty acids to form other important compounds, such as eicosanoids.
Sterols
a category of lipids that includes cholesterol. These are hydrocarbons with several rings in their structures
Ester
a chemical combination of an organic acid (e.g., fatty acid) and an alcohol. When hydrogen from the alcohol combines with the acid's hydrogen and oxygen, water is released and as ester linkage is formed; a triglyceride is an ester of three fatty acids and glycerol
Phosphate Group
a chemical group that contains phosphate (-PO4) attached to a larger molecule. Attaching this, along with two fatty acids, to a glycerol backbone forms a phospholipid
Hydrogenation
a chemical reaction in which hydrogen atoms are added to carbon-carbon double bonds; converting them to single bonds; hydrogenation of monounsaturated and polyunsaturated fatty acids reduce the number of double bonds they contain, thereby making them more saturated
Squalene
a cholesterol precursor found in whale liver and plants
Eicosanoids
a class of hormone-like substances formed in the body from long-chain fatty acids
Esterification
a condensation reaction in which an organic acid (e.g., fatty acid) combines with an alcohol with loss of water, creating an ester
Alphpa-Linolenic Acid (ALA)
an essential omega-3 fatty acid that contains 18 carbon atoms and three carbon-carbon double bonds
Linoleic Acid
an essential omega-6 fatty acid that contains 18 carbon atoms and two carbon-carbon double bonds
Omega-9 Fatty Acids
any polyunsaturated fatty acid in which the first double bond is nine carbons from the methyl end of the carbon chain
Omega-6 Fatty Acids
any polyunsaturated fatty acid in which the first double bond is six carbons from the methyl end of the carbon chain
Omega-3 Fatty Acids
any polyunsaturated fatty acid with the first double bond on the third carbon from the methyl end (-CH3)
Lipophilic
attracted to fat and fat solvents; fat-soluble
Adipose Tissue
body fat tissue
Hydrophilic
can mix with or dissolve in water (water-loving); hydrophilic compounds are polar and soluble in water
_____ is a nitrogen-containing compound that is part of phosphatidylcholine, a phospholipid. It also is part of the neurotransmitter acetylcholine. The body can synthesize it from the amino acid methionine.
choline
A _____ is a large lipoprotein formed in intestinal cells following the absorption of dietary fats. It has a central core of triglycerides and cholesterol surrounded by phospholipids and proteins.
chylomicron
A _____ is an unsaturated fatty acid with a bent carbon chain. Most naturally occurring unsaturated fatty acid are these.
cis fatty acid
Fatty Acids
compounds containing a long hydrocarbon chain with a carboxyl (-COOH) group at one end and a methyl group (CH3) at the other end
Phospholipids
compounds that consist of a glycerol molecule bonded to two fatty acid molecules and a phosphate group with a nitrogen-containing component. These have both water-soluble and fat-soluble regions, which make them good emulsifiers
Fat Replacers
compounds that imitate the functional and sensory properties of fats, but contain less available energy than fats
The blood lipoproteins that contain high levels of protein and low levels of triglycerides are called _____. Synthesized primarily in the liver and small intestine, these lipoproteins pick up cholesterol released from dying cells and other sources and transfer it to the lipoproteins. They are sometimes called "good cholesterol."
high-density lipoproteins (HDL)
Lecithin
in the body, a phospholipid with the nitrogenous component choline; in foods, lecithin is a blend of phospholipids with different nitrogenous components
Desaturation
insertion of double bonds into fatty acids to change them into new fatty acids
Hydrophobic
insoluble in water (water-fearing)
Enterocytes
intestinal cells
In the body, _____ is a phospholipid with the nitrogen-containing component choline. In foods, it is a blend of phospholipids with different nitrogen-containing components.
lecithin
_____ is an essential omega-6 fatty acid that contains 18 carbon atoms and 2 carbon-carbon double bonds; it is a thin liquid at room temperature.
linoleic acid
The major enzyme responsible for the breakdown of lipoproteins and triglycerides in the blood is _____.
lipoprotein lipase
A _____ is a complex that transports lipids in the lymph and blood. It consists of a central core of triglycerides and cholesterol surrounded by a shell composed of proteins, cholesterol, and phospholipids. The various types differ in size, composition, and density.
lipoproteins
_____ are the cholesterol-rich lipoproteins that result from the breakdown and removal of triglycerides from IDL. They are sometimes called "bad cholesterol."
low-density lipoproteins (LDL)
Diglycerides
molecules composed of glycerol combined with two fatty acids
A molecule of glycerol combined with one fatty acid is a _____.
monoglycerides
A fatty acid in which the carbon chain contains one or more double bond is an _____.
monounsaturated fatty acid (MUFA)
_____ are fatty acids that your body can make when they are needed. It is not necessary to consume them in the diet.
nonessential fatty acids
_____ is a fat replacer that is made from a sucrose backbone with six to eight fatty acids attached. The fatty acid arrangement prevents breakdown by the digestive enzyme lipase, so the fatty acids are not absorbed. It can withstand heat and is stable at frying temperatures. Trade name is Olean.
olestra
Oxidation
oxygen attaches to the double bonds of unsaturated fatty acids. It causes fats to become rancid
_____ are compounds that consist of a glycerol molecule bonded to two fatty acid molecules and phosphate group with a nitrogen-containing component. They have both water-soluble and fat-soluble regions, which make them good emulsifiers.
phospholipids
Streatorrhea
production of stools with an abnormally high amount of fat
A fatty acid completely filled by hydrogen, with all carbons in the chain linked by single bonds is a _____.
saturated fatty acid
Lanugo
soft, downy hair that covers a normal fetus from the fifth month but is shed almost entirely by the time of birth; it also appears on semi-starved individuals who have lost much of their body fat, serving as insulation normally provided by body fat
Phytosterols
sterols found in plants. These are poorly absorbed by humans and reduce intestinal absorption of cholesterol. They recently have been introduced as a cholesterol-lowering food ingredient
High-Density Lipoproteins (HDL)
the blood lipoproteins that contain high levels of protein and low levels of protein and low levels of triglycerides; synthesized primarily in the liver and small intestine, HDL pick up cholesterol released from dying cells and other sources and transfer it to other lipoproteins
Low-Density Lipoproteins (LDL)
the cholesterol-rich lipoproteins that result from the breakdown and removal of triglycerides from intermediate-density lipoprotein in the blood
Micelles
tiny emulsifying fat packets that can enter enterocytes; the complexes are composed of emulsifier molecules oriented with their hydrophobic part facing inward and their hydrophilic part facing outward toward the surrounding aqueous environment
A _____ is a monounsaturated fatty acid in which the hydrogens surrounding a double bond are on opposite sides of the carbon chain.
trans fatty acid
A _____ is an unsaturated fatty acid with a straighter chain than a cis fatty acid, usually as a result of hydrogenation; it is more solid than a cis fatty acid.
trans fatty acid
Cis Fatty Acid
unsaturated fatty acid in which the hydrogens surrounding a double bond are both on the same side of the carbon chain, causing a bend in the chain; most naturally occurring unsaturated fatty acids are cis fatty acids
Trans Fatty Acids
unsaturated fatty acids in which the hydrogens surrounding a double bond are on opposite sides if the carbon chain; this straightens the chain, and the fatty acid becomes more solid
_____ are triglyceride-rich lipoproteins formed in the liver that, when they enter the blood stream, are gradually accepted upon by lipoprotein lipase, releasing triglycerides to body cells.
very low-density lipoproteins (VLDL)
