Chapter 5: Understanding Nutrition

Glycerol

an alcohol composed of a three-carbon chain, which can serve as the backbone for a triglyceride.

lipids are composed of

carbon, hydrogen, oxygen

Renata eats a meal containing some fats. Within ________ hours after absorption, her body has removed the chylomicrons from her blood.

14

The DRI suggests a diet that provides ________ of the daily energy intake from fat.

20 to 35%

Cholesterol intakes in the U.S. average ________ milligrams for men.

315

Surveys show that most diets in the U.S. provide about ________ of their total energy from fat.

33%

Diets with up to ________ of kcalories from fat can be compatible with good health if energy intake is reasonable.

35%

Calculate a personal daily fat allowance for a person with an energy intake of 1700 kilocalories and a goal of 25% of kilocalories from fat.

47 grams

According to the DRI, what percentage of the daily energy intake should be provided by linoleic acid?

5 to 10

Fats carry with them the four fat-soluble vitamins

A, D, E, and K - together with many of the compounds that give foods their flavor, texture, and palatability.

Which statement about lipid digestion is FALSE?

Bile is a digestive enzyme that acts as an emulsifier.

What are chylomicrons?

Clusters of lipids and proteins used as transport vehicles from the intestines to the body

these are examples of sterols

Cortisol Vitamin D Estrogen Cholesterol

Which of the following is not a benefit of eating almonds or walnuts?

Decreasing blood-clotting factors

groups of lipoproteins

HDL VLDL LDL chylomicrons

When the body is deprived of food, which enzyme hydrolyzes triglycerides so that their parts enter general circulation and are available to other cells?

Hormone-sensitive lipase

potential side effects of high intakes of omega-3 polyunsaturated fatty acids?

Interference in wound healing Higher LDL cholesterol Suppressed immune functions increasing bleeding time

Linolenic acid is an omega-3 fatty acid. What does "omega-3" mean?

Its closest double bond is three carbons away from the methyl end.

elevated blood _______ cholesterol is a major risk factor for cardiovascular disease (CVD)

LDL - In contrast, elevated blood HDL cholesterol levels indicate a decreased risk of heart disease. HDLs are a type of lipoprotein that remove cholesterol from cells and carry it back to the liver for disposal or recycling.

Which statement accurately describes essential fatty acids?

Most diets in the U.S. meet the minimum fatty acid requirement.

Which statement about fat replacers is FALSE?

Olestra is an artificial fat that delivers a small amount of energy.

Every triglyceride contains

One molecule of glycerol & three fatty acids

Which statement best describes characteristics of solid fats and oils?

The longer the carbon chain, the softer the fat at room temperature.

Which lipid is most abundant, in foods and in the body?

Triglycerides

margarine

a butter substitute made primarily of hydrogenated vegetable oils and sometimes blended with animal fats, emulsifiers, water, milk, salt, vitamins, artificial color, and other ingredients.

Phospholipids

a compound similar to a triglyceride but having a phosphate group (a phosphorus-containing salt) and choline (or another nitrogen-containing compound) in place of one of the fatty acids.

Hydrophobic

a term referring to water-fearing, or non-water-soluble, substances; also known as lipophilic (fat loving).

antioxidants

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

What is the main cause of cardiovascular disease?

atherosclerosis

Some research suggests that both naturally occurring and commercially created trans fats change blood lipids similarly; other research suggests that the negative effects are specific to only the

commercial trans fats

All of the following are recommendations for dietary fat and cholesterol intake EXCEPT:

consuming at least 300 mg of cholesterol per day

omega-3 fatty acid family

develop from linolenic acid

Omega-6 fatty acid family

develops from linoleic acid

Chylomicrons transport

dietary lipids to the body cells - Chylomicrons are a type of lipoprotein made in the small intestine that transport lipids from the diet to the rest of the body. Very low density lipoproteins (VLDLs) are lipoproteins that transport lipids made in the liver.

Lipids

emulsified by bile and digested by lipases into fatty acids, glycerol, and monoglycerides. The digested triglycerides diffuse into intestinal cells in the form of micelles where they can be reassembled into new triglycerides. provide energy, insulate against temperature extremes, protect against shock and maintain cell membranes.

few fatty acids occur...

free in foods or in the body... - most are incorporated into triglycerides.

All fatty acids have

have the same basic structure- a chain of carbon and hydrogen atoms with an acid group (COOH) at one end and a methyl group (CH3) at the other end

Eicosanoids

hormone-like compounds that have a localized effect

Adipokines

hormones secreted by adipose tissue

the double bond

is a point of unsaturation.

fatty acids

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 - may be saturated or unsaturated. unsaturated have one or more points of unsaturation- monounsaturated or polyunsaturated

In comparison to a low-density lipoprotein, a high-density lipoprotein contains ____.

more protein

essential fatty acids

must be supplied by the diet

The Seven Countries Study found that Mediterranean countries have low rates of heart disease because they consume more _________ in their diet.

olive oil

Which of the following is a potentially healthful source of monounsaturated fats?

olives

Which is not a potential side effect of high intakes of omega-3 polyunsaturated fatty acids?

rapid heartbeat

In the body, trans-fatty acids behave more like

saturated fats, increasing blood cholesterol and the risk of heart disease—a major health disadvantage.

Current food labels list total fat, saturated fat, trans fat, and cholesterol contents of foods. Because each package provides information for a single serving and because serving sizes are standardized, consumers can easily compare

similar products

Which food source is rich in lecithin?

soybeans

the degree of unsaturation influences

stability. - all fats become spoiled when exposed to oxygen.

Lipids that have a multiple ring structure are called

sterols

monounsaturated fats

tend to belong to the omega-9 group so does oleic acid, which is the most predominant monounsaturated fatty acid in the diet

Oxidation

the process of a substance combining with oxygen; oxidation reactions involve the loss of electrons. - produces a variety of compounds that smell and taste rancid - exposure to heat and light can speed up rancidity

Although some fat in the diet is necessary, too much fat adds kcalories without nutrients, which leads to obesity and nutrient inadequacies. Too much saturated fat and trans fat increases the risk of heart disease and possibly cancer. For these reasons, health authorities recommend a diet moderate in total fat and low in saturated fat and _____ ______

trans fat

if hydrogens are missing and there is at least one double bond...

unsaturated fatty acid

in the liver—the most active site of lipid synthesis—cells are making cholesterol, fatty acids, and other lipid compounds. Ultimately, the lipids made in the liver and those collected from chylomicron remnants are packaged with proteins as a VLDL (very-low-density lipoproteins) and shipped to other parts of the body. As the VLDL travel through the body, cells remove triglycerides, causing the proportion of lipids to shift. Cholesterol becomes the predominant lipid, and the lipoprotein becomes smaller and more dense. As this occurs, the VLDL become LDL (low-density lipoproteins), loaded with cholesterol, but containing relatively few triglycerides.

very low-density lipoproteins (VLDL): lipoproteins made by the liver that transport lipids (primarily triglycerides) from the liver to other tissues. low-density lipoproteins (LDL): lipoproteins that derive from VLDL and transport lipids (primarily cholesterol) in the blood.

lipids

a family of compounds that includes triglycerides, phospholipids, and sterols. Lipids are characterized by their insolubility in water. (Lipids also include the fat-soluble vitamins.) - have more carbons and hydrogens in proportion to their oxygens - can supply more energy per gram than carbohydrates

saturated fatty acid

a fatty acid carrying the maximum possible number of hydrogen atoms—for example, stearic acid. A saturated fat is composed of triglycerides in which most of the fatty acids are saturated. - ex.: stearic acid

polyunsaturated fatty acid

a fatty acid that lacks four or more hydrogen atoms and has two or more double bonds between carbons; abbreviated PUFA. Examples include linoleic acid (two double bonds) and linolenic acid (three double bonds). A polyunsaturated fat is composed of triglycerides in which most of the fatty acids are polyunsaturated. poly = many

Which of the following is not a sterol?

bile

______ emulsifies fat, whereas ______ digests fat

bile; lipase - Fat (predominantly triglyceride) enters the small intestine as large fat globules. Bile emulsifies the fat into small droplets so that pancreatic lipase can begin to remove the outer fatty acids from the triglyceride. Lipases cannot efficiently digest large globules of fat.

Some fats in the diet are essential for good health but high intakes of solid fats can be harmful. Both the amounts and types of fat in the diet influence the risk for

disease

The body uses the 20-carbon omega-3 and omega-6 fatty acids to make substances known as eicosanoids (eye-COSS-uh-noyds). Eicosanoids are a diverse group of more than 100 compounds. Sometimes described as "hormonelike," eicosanoids differ from hormones in important ways. For one, 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 in the same localized area. For another, hormones elicit the same response from all their target cells, whereas eicosanoids may have different effects on different cells. The actions of various eicosanoids sometimes oppose one another. For example, one causes muscles to relax and blood vessels to dilate, whereas another causes muscles to contract and blood vessels to constrict. Certain eicosanoids participate in the immune response to injury and infection, producing fever, inflammation, and pain. One of the ways aspirin relieves these symptoms is by slowing the synthesis of these eicosanoids.

eicosanoids: derivatives of 20-carbon fatty acids; biologically active compounds that help regulate blood pressure, blood clotting, and other body functions. They include prostaglandins, thromboxanes, and leukotrienes. - Eicosanoids that derive from omega-3 fatty acids differ from those that derive from omega-6 fatty acids, with the omega-3 family providing greater health benefits. In general, the omega-6 fatty acids have a pro-inflammatory effect and the omega-3 fatty acids have an anti-inflammatory effect—and atherosclerosis is an inflammatory disease. The omega-3 eicosanoids help lower blood pressure, prevent blood clot formation, protect against irregular heartbeats, and reduce inflammation, whereas the omega-6 eicosanoids tend to promote clot formation, inflammation, and blood vessel constriction.

Linolenic acid is an essential fatty acid and the 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 and docosahexaenoic acid, respectively. These omega-3 fatty acids play critical roles in the optimal structure and function of cells. Found abundantly in the eyes and brain, the omega-3 fatty acids are essential for normal growth, visual acuity, and cognitive development. They may also play an important role in the prevention and treatment of heart disease, as later sections explain.

eicosapentaenoic acid (EPA): an omega-3 polyunsaturated fatty acid with 20 carbons and five double bonds; present in fatty fish and synthesized in limited amounts in the body from linolenic acid. docosahexaenoic acid (DHA): an omega-3 polyunsaturated fatty acid with 22 carbons and six double bonds; present in fatty fish and synthesized in limited amounts in the body from linolenic acid.

Cholesterol made within the body is referred to as ________.

endogenous

Heart Disease Replacing saturated fats with unsaturated fats reduces LDL cholesterol and lowers the risk of heart disease and related deaths. To replace saturated fats with unsaturated fats, sauté foods in olive oil instead of butter, garnish salads with sunflower seeds instead of bacon, snack on mixed nuts instead of potato chips, use avocado instead of cheese on a sandwich, and eat salmon instead of steak.

simple substitutions can lower the saturated fat and raise the unsaturated fat in a meal

Most lipid digestion occurs in the

small intestine -because bile is only secreted into the small intestine, not into the stomach. Bile emulsifies the fat, enabling lipase to hydrolyze lipids.

Which is not a group of lipoproteins?

VHDL

hydrogenation

a chemical process by which hydrogens are added to monounsaturated or polyunsaturated fatty acids to reduce the number of double bonds, making the fats more saturated (solid) and more resistant to oxidation (protecting against rancidity). Hydrogenation produces trans-fatty acids. - total hydrogenation rarely occurs in food processing.

Other Diseases Limited research suggests that the omega-3 fatty acids of fish may protect against asthma, pancreatitis, and rheumatoid arthritis. Omega-3 fats also appear to play a role in improving

memory and cognition

According to surveys, diets in the United States provide about 33 percent of their total energy from fat, with saturated fat contributing about 11 percent of the total. The average daily intake of trans-fatty acids in the United States is 1.3 grams per day—mostly from products that have been hydrogenated. Cholesterol intakes in the United States average 221 milligrams a day for women and 315 for men.

Although it is very difficult to do, some people actually manage to eat too little fat—to their detriment. Among them are people with eating disorders, described in Highlight 8, and athletes. Athletes following a diet too low in fat (less than 20 percent of total kcalories) fall short on energy, vitamins, minerals, and essential fatty acids as well as on performance. As a practical guideline, it is wise to include the equivalent of at least a teaspoon of fat in every meal—a little peanut butter on toast or mayonnaise in tuna salad, for example. Dietary recommendations that limit fat are designed for healthy people older than age 2; Chapter 16 discusses the fat needs of infants and young children.

According to the Mediterranean Diet Pyramid, how often should one eat fish and seafood?

At least twice a week

Are some fats "good," and others "bad" from the body's point of view? The saturated and trans fats do indeed seem mostly bad for the health of the heart. Aside from providing energy, which unsaturated fats can do equally well, saturated and trans fats bring no benefits to the body. Furthermore, no harm can come from consuming diets low in them. Still, some foods rich in these fats are often delicious, giving them an occasional place in the diet. In contrast, the unsaturated fats are mostly good for heart health when consumed in moderation.

Clearly, different fatty acids have different actions in the body and risks of chronic diseases. When judging foods by their fatty acids, keep in mind that the fat in foods is a mixture of both unsaturated and saturated fatty acids. Even predominantly monounsaturated olive oil delivers some saturated fat. Consequently, even when a person chooses foods with mostly unsaturated fats, saturated fat can still add up if total fat is too high. Focusing all efforts on simply lowering saturated fat in the diet may be narrow advice for heart health. Including vegetables, fruits, whole grains, and legumes as part of a balanced daily diet is a good idea, as is replacing saturated fats such as butter, shortening, and meat fat with unsaturated fats such as olive oil and the oils from nuts and fish. These foods provide beneficial fatty acids, fiber, vitamins, minerals, and phytochemicals as well as little (or no) salt, saturated fat, and trans fat—all valuable in protecting the body's health. In addition, take care to select portion sizes that will best meet energy needs. And enjoy some physical activity daily. Remember that even a healthy eating pattern can be detrimental if foods are eaten in excess.

Dietary guidelines for fat have shifted emphasis from limiting total fat, in general, to lowering saturated and trans fat, specifically. Instead of urging people to cut back on all fats, recommendations suggest carefully replacing the "bad" saturated fats with the "good" unsaturated fats and enjoying them in moderation. The goal is to create a diet moderate in kcalories that provides enough of the fats that support good health, but not too much of those that harm health.

Dietary Reference Intakes (DRI) committee suggests a healthy range of 20 to 35 percent of energy intake from fat. This range appears to be compatible with low rates of heart disease, diabetes, obesity, and cancer. Heart-healthy recommendations suggest that within this range, consumers should try to minimize their intakes of saturated fat and trans fat and use unsaturated, especially polyunsaturated, fats instead. Replacing saturated fats with monounsaturated fats or carbohydrates from whole grains also lowers the risks of heart disease some, but using carbohydrates from refined starches and added sugars increases risks

Tree nuts and peanuts are traditionally excluded from low-fat diets. Nuts provide up to 80 percent of their kcalories from fat, and a quarter cup (about an ounce) of mixed nuts provides more than 200 kcalories. Frequent nut consumption, however, correlates with lower risk of mortality and chronic diseases, such as diabetes and heart disease. Benefits are seen for a variety of nuts commonly eaten in the United States: almonds, Brazil nuts, cashews, hazelnuts, macadamia nuts, pecans, pistachios, walnuts, and even peanuts. On average, these nuts contain mostly monounsaturated fat (59 percent), some polyunsaturated fat (27 percent), and little saturated fat (14 percent). Nuts also provide valuable fiber, vegetable protein, vitamin E, minerals, and phytochemicals.

Including nuts may be a wise diet strategy against heart disease (see Photo H5-2). Nuts may protect against heart disease by lowering blood cholesterol and blood pressure, and by limiting oxidative stress and inflammation. Some research suggests that a diet that includes nuts may benefit other diseases as well. Because most of the energy nuts provide comes from fats, they deliver many kcalories per bite. Incorporating nuts in the diet, however, does not necessarily lead to weight gains and may even help with weight control by providing satiety. Consumers can enjoy nuts without increasing total kcalories by using nuts instead of, not in addition to, other foods.

true statements about lipid digestion

Pancreatic lipase removes each of a triglyceride's fatty acids, leaving a monoglyceride. When fat enters the small intestine, it triggers the release of CCK and bile. Gastric lipase is responsible for only a small amount of fat digestion. Lingual lipase plays an active role in fat digestion in infants.

Defining the exact amount of saturated fat or trans fat that begins to harm health is difficult. For this reason, no RDA or Upper Level has been set. Instead, 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, and as little trans fat as possible. In the 1960s, guidelines began to advise limiting dietary cholesterol to lower blood cholesterol and the risk of heart disease, but decades of research no longer support such advice. For this reason, current dietary guidelines no longer limit consumption of dietary cholesterol to 300 milligrams per day, but instead suggest that individuals eat as little dietary cholesterol as possible while consuming a healthy eating pattern.

These recommendations recognize that diets with up to 35 percent of kcalories from fat can be compatible with good health if energy intake is reasonable and saturated fat and trans fat intakes are low. When total fat exceeds 35 percent, however, saturated fat usually rises to unhealthy levels. For a 2000-kcalorie diet, 20 to 35 percent represents 400 to 700 kcalories from fat (roughly 45 to 75 grams)

omega-6 fatty acid

a polyunsaturated fatty acid in which the closest double bond to the methyl end of the carbon chain is six carbons away.

lipases

enzymes that hydrolyze lipids (fats). Lingual lipase is a fat-digesting enzyme secreted from the salivary gland at the base of the tongue; gastric lipase is a fat-digesting enzyme secreted from the cells of the stomach.

Fat replacers offering the sensory and cooking qualities of fats but none of the kcalories are called artificial fats. A familiar example of an artificial fat that has been approved for use in snack foods such as potato chips, crackers, and tortilla chips is olestra. Olestra's chemical structure is similar to that of a triglyceride but with important differences. A triglyceride is composed of a glycerol molecule with three fatty acids attached, whereas olestra is made of a sucrose molecule with six to eight fatty acids attached. Enzymes in the digestive tract cannot break the bonds of olestra, so unlike sucrose or fatty acids, olestra passes through the digestive system unabsorbed.

- artificial fats: zero-energy fat replacers that are chemically synthesized to mimic the sensory and cooking qualities of naturally occurring fats but are totally or partially resistant to digestion. - olestra: a synthetic fat made from sucrose and fatty acids that provides 0 kcalories per gram; also known as sucrose polyester.

mediterranean diet - the incidence of heart disease, some cancers, diabetes, and other chronic inflammatory diseases is low, and life expectancy is high - no one factor alone can be credited with reducing disease risks—the association holds true only when the overall eating pattern is present. Apparently, each of the foods contributes small benefits that harmonize to produce either a substantial cumulative or synergistic effect.

- fresh, whole foods. crusty breads, whole grains, potatoes, and pastas; a variety of vegetables (including wild greens) and legumes; feta and mozzarella cheeses and yogurt; nuts; and fruits (especially grapes and figs). They eat some fish, other seafood, poultry, a few eggs, and little meat. Along with olives and olive oil, their principal sources of fat are nuts and fish; they rarely use butter or encounter hydrogenated fats. They commonly use herbs and spices instead of salt. Consequently, traditional Mediterranean diets are low in saturated fat and very low in trans fat.

hydrogenation offers two food-processing advantages:

- it protects against oxidation (thereby prolonging shelf life) by making polyunsaturated fats more saturated. - it alters the texture of foods by making liquid vegetable oils more solid (as in margarine and shortening) extra: hydrogenated fats make margarine spreadable, pie crusts flaky, and puddings creamy

how to protect fat-containing products against rancidity (three ways)

- products may be sealed in air-tight, nonmetallic containers, protected from light, and refrigerated—an expensive and inconvenient storage system. - manufacturers may add antioxidants to compete for the oxygen and thus protect the oil (examples are the additives BHA and BHT and vitamin E). - products may undergo a process known as hydrogenation.

The traditional diets of countries in the Mediterranean region offer an excellent example of eating patterns that freely use "good" fats. The primary fat in these diets is olive oil, which seems to play a key role in providing health benefits. A classic study of the world's people, the Seven Countries Study, found that death rates from heart disease were strongly associated with diets high in saturated fats but only weakly linked with total fat. In fact, the two regions with the highest fat intakes, Finland and the Greek island of Crete, had the highest (Finland) and lowest (Crete) rates of heart disease deaths. In both countries, the people consumed 40 percent or more of their kcalories from fat. Clearly, a high-fat diet is not the primary problem. When researchers refocused their attention on the type of fat, they noticed the benefits of olive oil.

A diet that uses olive oil instead of other fats, especially butter, stick margarine, and meat fats, offers numerous health benefits (see Photo H5-1). Olive oil, canola oil, and other oils rich in monounsaturated fatty acids help protect against heart disease and stroke by lowering blood-clotting factors, blood pressure, and total and LDL cholesterol (but not HDL cholesterol); reducing LDL susceptibility to oxidation; interfering with the inflammatory response; and providing antimicrobial actions.

Fat also makes a slightly greater contribution to energy needs during extended periods of food deprivation. When energy needs are not being met, several lipase enzymes (most notably hormone-sensitive lipase) inside the adipose cells respond by dismantling stored triglycerides and releasing the glycerol and fatty acids directly into the blood. Energy-hungry cells throughout the body can then capture these compounds and take them through a series of chemical reactions to yield energy, carbon dioxide, and water. - hormone-sensitive lipase: an enzyme inside adipose cells that responds to the body's need for fuel by hydrolyzing triglycerides so that their parts (glycerol and fatty acids) enter the general circulation and thus become available to other cells for fuel. The signals to which this enzyme responds include epinephrine and glucagon, which oppose insulin.

A person who fasts (drinking only water) will rapidly metabolize body fat. Even with abundant body fat, the person has to obtain some energy from lean protein tissue because the brain, nerves, and red blood cells need glucose—and without carbohydrate, only protein and the small glycerol molecule of a triglyceride can be converted to glucose; fatty acids cannot be. Still, in times of severe hunger and starvation, a fatter person can survive longer than a thinner person thanks to the energy reserve of adipose tissue. But as Chapter 7 explains, fasting for too long will eventually cause death, even if the person still has ample body fat.

Interest in the health benefits of the long-chain omega-3 polyunsaturated fatty acids began almost 50 years ago, when researchers reported that the native peoples of Alaska, northern Canada, and Greenland—who eat a traditional diet rich in omega-3 fatty acids, notably EPA (eicosapentaenoic acid) and DHA (docosaheaenoic acid)—had a remarkably low rate of heart disease even though their diets were high in fat. More recently, a review of this early study revealed that the prevalence of heart disease among these people was not carefully investigated, and therefore the original premise was faulty. The traditional dietary pattern associated with these native people may raise blood cholesterol slightly, but it is not associated with heart disease risk. Decades of research has confirmed that omega-3 fatty acids help protect against heart disease by reducing blood triglycerides, blood pressure, resting heart rate, and inflammation; stabilizing plaque; and serving as precursors to eicosanoids. For people with hypertension or atherosclerosis, these actions can be lifesaving.

Because increasing omega-3 fatty acids in the diet supports heart health and lowers the rate of deaths from heart disease, the American Heart Association recommends including fish in a heart-healthy diet. Consumers in the United States currently receive only about one-third of the 8-ounce weekly recommendation of seafood. People who eat some fish each week can lower their risks of heart attack and stroke fish is a good source of the omega-3 fatty acid, but it contains mercury- an environmental contaminant

Recall that cholesterol is found in all foods derived from animals. Consequently, eating fewer meats, eggs, and milk products helps lower dietary cholesterol intake (as well as total and saturated fat intakes). Most foods that are high in cholesterol are also high in saturated fat, but eggs are an exception. An egg contains only 1 gram of saturated fat but has a little more than 200 milligrams of cholesterol—roughly two-thirds of the previous cholesterol recommendation, which explains why people fighting heart disease were told to limit their egg consumption. For most people, however, eating eggs does not increase the risk of heart disease. In fact, the 2015 Dietary Guidelines concluded that there is no appreciable relationship between the consumption of dietary cholesterol and blood cholesterol or heart disease.

Eggs are a valuable part of the diet because they are inexpensive, useful in cooking, and a source of high-quality protein, other nutrients, and phytochemicals. To help consumers improve their omega-3 fatty acid intake, hens fed flaxseed, fish oil, or marine algae produce eggs rich in omega-3 fatty acids (up to 200 milligrams per egg). Including even one enriched egg in the diet daily can significantly increase a person's intake of omega-3 fatty acids. Food manufacturers have produced several fat-free, cholesterol-free egg substitutes.

Omega-6 to Omega-3 Ratio - Because omega-6 and omega-3 fatty acids compete for the same enzymes and their actions often oppose each other, researchers have studied whether there is an ideal ratio that best supports health. Suggested ratios range from 4:1 to 10:1; while some researchers support such recommendations, others find the ratio of little value in improving health or predicting risk. Increasing the amount of omega-3 fatty acids in the diet is clearly beneficial, but reducing the amount of omega-6 fatty acids in the diet to improve the ratio may not be helpful. Omega-6 fatty acids protect heart health by lowering LDL cholesterol and improving insulin resistance.

Fatty Acid Deficiencies - Most diets in the United States meet the minimum essential fatty acid requirement adequately. Historically, deficiencies have developed only in infants and young children who have been fed fat-free milk and low-fat diets or in hospital clients who have been mistakenly fed formulas that provided no polyunsaturated fatty acids for long periods of time. Classic deficiency symptoms include growth retardation, reproductive failure, skin lesions, kidney and liver disorders, and subtle neurological and visual problems.

In general, except for seafood, animal fats tend to have a higher proportion of saturated fatty acids. Except for the tropical oils, plant foods tend to have a higher proportion of monounsaturated and polyunsaturated fatty acids. Consumers can find an abundant array of fresh, unprocessed foods that are naturally low in saturated fat and trans fat. In addition, many familiar foods have been processed to provide less saturated and trans fat. For example, saturated fat is removed by skimming milk or trimming meats. Manufacturers can use fat-free milk in creamy desserts and lean meats in frozen entrées. Sometimes manufacturers simply prepare the products differently.

For example, potato chips may be baked instead of fried. Such choices make healthy eating easy.

The distinction between LDL and HDL has implications for the health of the heart and blood vessels. The blood lipid linked most directly to heart disease is LDL cholesterol. As mentioned, HDL also carry cholesterol, but elevated HDL represent cholesterol returning from the rest of the body to the liver for breakdown and excretion. The transport of cholesterol from the tissues back to the liver is sometimes called reverse cholesterol transport or the scavenger pathway.

High LDL and low HDL cholesterol are both associated with a high risk of heart disease. Having adequate HDL is beneficial, but having high HDL is not necessarily more beneficial. Some people think of HDL as healthy and LDL as lousy, or refer to LDL as "bad," and HDL as "good," cholesterol. Keep in mind that the cholesterol itself is the same and that the differences between LDL and HDL reflect the proportions and types of lipids and proteins within them—not the type of cholesterol.

the FDA advises pregnant and lactating women, women of childbearing age who may become pregnant, and young children to include fish in their diets, but to avoid tilefish (also called golden snapper or golden bass), swordfish, king mackeral, marlin, and shark. They are also advised to limit average weekly consumption of a variety of ocean fish and shellfish to 12 ounces (cooked or canned) and white (albacore) tuna to 6 ounces (cooked or canned). Commonly eaten seafood relatively low in mercury include shrimp, catfish, pollock, salmon, and canned light tuna.

In addition to the direct toxic effects of mercury, some research suggests that mercury may diminish the health benefits of omega-3 fatty acids. Such findings serve as a reminder that our health depends on a healthy environment.

Which blood lipid is linked most directly to heart disease?

Low-density lipoprotein

benefits of eating almonds or walnuts

Lower mortality Providing satiety Lower blood cholesterol and blood pressure limiting oxidative stress

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. (Remember from Chapter 3 that bile is a digestive secretion that is made by the liver, stored in the gallbladder, and released into the small intestine when needed.) 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. Having both water-soluble and fat-soluble ends enables bile to act as an emulsifier—a substance that promotes the mixing of fat molecules in the surrounding watery fluids. Note that bile is not a digestive enzyme; it is, however, essential in preparing fats for digestion by the lipase enzymes from the pancreas and small intestine.

Most of the hydrolysis of triglycerides occurs in the 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. Occasionally, enzymes remove all three fatty acids, leaving a free molecule of glycerol. Phospholipids are digested similarly—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.

mediterranean diet - people can receive as much as 40 percent of a day's kcalories from fat, but their limited consumption of milk and milk products and meats provides less than 10 percent from saturated fats. In addition, because the animals in the Mediterranean region pasture-graze, the meat, milk and milk products, and eggs are richer in omega-3 fatty acids than those from animals fed grain.

Other foods typical of the Mediterranean region, such as wild plants and snails, provide omega-3 fatty acids as well. All in all, the traditional Mediterranean diet has earned a reputation for its health benefits as well as its delicious flavors. Consumers need to beware that the typical Mediterranean-style cuisine available in US restaurants, however, has been adjusted to popular tastes. Quite often, these meals are much higher in saturated fats and meats—and much lower in the polyunsaturated fats and vegetables—than the traditional fare. Unfortunately, it appears that people in the Mediterranean region who are replacing some of their traditional dietary habits with those of the United States are losing the health benefits previously enjoyed.

Which term describes the process of a substance combing with oxygen?

Oxidation

According to the Mediterranean Diet Pyramid, how often should one eat meat?

No more than a few times a month

The fat cells of the adipose tissue readily take up and store triglycerides.

Other body cells store only small amounts of fat for their immediate use; fat accumulation in nonadipose cells is toxic and impairs health. This scenario occurs when the diet delivers excesses and the liver increases its fat production. Fatty liver linked to obesity causes chronic inflammation, which can advance to fibrosis, cirrhosis, and cancer.

The Percent Daily Value describes the amount of fat in a food, as a percent of the Daily Value for fat. The percent kcalories of fat is the percentage of the total kcalories of fat in the food. Assume you purchased a frozen macaroni cheese product that provides 250 kcalories and 12 grams of fat. The Daily Value for fat is 65 grams, based on a 2000-kcalorie diet. Part 1: Calculate the Percent Daily Value for the Macaroni and Cheese. Part 2: Calculate the percent of fat kcalories in the Macaroni and Cheese. Part 3: Which number will provide you with an accurate idea of how this choice affects the Daily Value recommendation?

Part 1: Percent Daily Value: 18.5% Part 2: Percent kcalories: 43.2% Part 3: Best choice: percent kcalories

Consumers need to keep in mind that low-fat and fat-free foods still deliver kcalories. Alternatives to fat can help lower energy intake and support weight loss only when they actually replace fat and energy in the diet.

Perhaps the best advice for consumers regarding fat in the diet would be to replace saturated fat with unsaturated fat (see Photo 5-6). Sometimes these choices can be difficult, though, because fats make foods taste delicious. To maintain good health, must a person give up all high-fat foods forever—never again to eat marbled steak, hollandaise sauce, or gooey chocolate cake? Not at all. These foods bring pleasure to a meal and can be enjoyed as part of a healthy diet when eaten occasionally in small quantities; but they should not be everyday foods. The key dietary principle for fat is moderation, not deprivation. Appreciate the energy and enjoyment that fat provides, but take care not to exceed your needs.

Despite common misconceptions, 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 referred to as endogenous (en-DODGE-eh-nus), whereas cholesterol from outside the body (from foods) is referred to as exogenous (eks-ODGE-eh-nus). Right now, as you read, your liver is manufacturing cholesterol from fragments of carbohydrate, protein, and fat. In fact, the liver makes about 800 to 1500 milligrams of cholesterol per day, thus contributing much more to the body's total than does the diet. For perspective, the Daily Value on food labels for cholesterol is 300 milligrams per day. Cholesterol's harmful effects in the body occur when it accumulates in the artery walls and contributes to the formation of plaque (PLACK). These plaque deposits lead to atherosclerosis (ATH-er-oh-scler-OH-sis), a disease that causes heart attacks and strokes. Chapter 18 provides many more details.

Phospholipids, including lecithin, have a unique chemical structure that allows them to be soluble in both water and fat. The food industry uses phospholipids as emulsifiers, and in the body, phospholipids are part of cell membranes. Sterols have a multiple-ring structure that differs from the structure of other lipids. In the body, sterols include cholesterol, bile, vitamin D, and some hormones. Animal-derived foods are rich sources of cholesterol. Table 5-2 summarizes the lipid family of compounds.

spoiling

Polyunsaturated fats spoil most readily because their double bonds are unstable; monounsaturated fats are slightly less susceptible. Saturated fats are most resistant to oxidation and thus least likely to become rancid.

Solid Fats and Oils Solid fats include the fats in meat and poultry (as in poultry skin, luncheon meats, and sausage); the fats in whole milk, cheeses, and butter; shortening (as in fried foods and baked goods); and hard margarines. Because solid fats deliver an abundance of saturated fatty acids, they are considered discretionary kcalories. The fats of fish, nuts, and vegetable oils are not counted as discretionary kcalories because they provide valuable omega-3 fatty acids, essential fatty acids, and vitamin E. When discretionary kcalories are available, they may be used to add fats in cooking or at the table or to select higher fat items from the food groups. Some solid fats, such as butter and the fat trimmed from meat, are easy to see. Others—such as the fat that "marbles" a steak or is hidden in foods such as cheese—are less apparent and can be present in foods in surprisingly high amounts. Any fried food contains abundant solid fats—potato chips, french fries, fried wontons, and fried fish. Many baked goods, too, are high in solid fats—pie crusts, pastries, crackers, biscuits, cornbread, doughnuts, sweet rolls, cookies, and cakes.

Reports on trans-fatty acids raise the question whether margarine or butter is a better choice for heart health. The American Heart Association has stated that because both the saturated fat of butter and the trans fat of hard stick margarine can raise blood cholesterol and contribute to heart disease, the best choices are soft margarines (liquid or tub). Soft margarines are less hydrogenated and relatively lower in trans-fatty acids; consequently, they do not raise blood cholesterol as much as the saturated fats of butter or the trans fats of hard (stick) margarines do. Read labels to determine how much trans fat a margarine contains. Many manufacturers are now offering nonhydrogenated margarines that are "trans-fat free." In addition, manufacturers have developed margarines fortified with plant sterols that lower blood cholesterol.

Heart Disease As mentioned earlier, elevated LDL cholesterol is a major risk factor for cardiovascular disease (CVD). As LDL cholesterol accumulates in the arteries, blood flow becomes restricted and blood pressure rises. The consequences are deadly; in fact, heart disease is the nation's number-one killer of adults. LDL cholesterol is often used to predict the likelihood of a person's suffering a heart attack or stroke; the higher the LDL, the earlier and more likely the tragedy. Much of the effort to prevent and treat heart disease focuses on lowering LDL cholesterol. Saturated fats are most often implicated in raising LDL cholesterol. In general, the more saturated fat in the diet, the more LDL cholesterol in the blood. Not all saturated fats have the same cholesterol-raising effect, however. 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. Making such distinctions may be impractical in diet planning, however, because these saturated fatty acids typically appear together in the same foods. In addition to raising blood cholesterol, saturated fatty acids contribute to heart disease by promoting blood clotting. Fats from animal sources (meats, milk, and milk products) are the main sources of saturated fats in most people's diets. Selecting lean cuts of meat, skinless poultry, and fat-free milk products helps lower saturated fat intake and the risk of heart disease.

Research also suggests an association between dietary trans fats and heart disease. In the body, trans fats alter blood cholesterol the same way some saturated fats do: they raise LDL cholesterol and lower HDL cholesterol. Limiting the intake of trans fats can improve blood cholesterol and lower the risks of heart disease and all-cause mortality. To that end, many restaurants and manufacturers have taken steps to eliminate or greatly reduce trans fats in foods. The decrease in trans fatty acids in the food supply is apparent in a decrease in plasma concentrations of trans fatty acids in consumers. Unlike saturated fat and trans fat, dietary cholesterol raises blood cholesterol very little, if at all. Furthermore, there is no clear relationship between dietary cholesterol and heart disease, which is complicated, in part, by the influence of more than 100 gene variations.

Total fat, saturated fat, and cholesterol are also expressed as "% Daily Values" for a person consuming 2000 kcalories. Using 35 percent of energy intake as the guideline for fat, the Daily Value is 78 grams of fat; using 10 percent for saturated fat, the Daily Value is 20 grams of saturated fat. The Daily Value for cholesterol is 300 milligrams regardless of energy intake. There is no Daily Value for trans fat, but consumers should try to keep intakes as low as possible and within the 10 percent allotted for saturated fat.

The % Daily Value for fat on food labels is based on 78 grams. To know how your intake compares with this recommendation, you can either count grams until you reach 78 or add the "% Daily Values" until you reach 100 percent—if your energy intake is 2000 kcalories a day. If your energy intake is more or less, you can calculate your personal daily fat allowance in grams. Suppose your energy intake is 1800 kcalories per day and your goal is 30 percent kcalories from fat. Multiply your total energy intake by 30 percent, then divide by 9:

What is the simplest of the 18-carbon fatty acids?

Stearic acid

Protein Foods The fats in seafood, nuts, and seeds are considered oils, whereas the fats in meat and poultry are considered solid fats. Because these meats provide high-quality protein and valuable vitamins and minerals, however, they can be included in a healthy diet if a person makes lean choices (see Table 5-6), prepares them using the suggestions outlined in How To 5-1, and eats small portions. When preparing meat, fish, or poultry, consider grilling, baking, or broiling, but not frying. Fried fish does not benefit heart disease; fried fish from fast-food restaurants and frozen fried fish products are often low in omega-3 fatty acids and high in trans- and saturated fatty acids.

The American Heart Association recommends eating at least two servings of fish a week, with an emphasis on fatty fish (salmon, herring, and mackerel, for example). Fish provides many minerals (except iron) and vitamins. Because fish is leaner than most other animal-protein sources it can help with weight-loss efforts. The combination of losing weight and eating fish improves blood lipids even more effectively than can be explained by either the weight loss or the omega-3 fats of the fish. Chapter 19 discusses the adverse consequences of mercury, an environmental contaminant common in some fish; in general, mercury is relatively high in tilefish (also called golden snapper or golden bass), swordfish, king mackerel, and shark and relatively low in cod, haddock, pollock, salmon, sole, tilapia, and most shellfish. Most healthy people who eat two servings of fish a week can maximize the health benefits while incurring minimal risks. Nonfish sources of omega-3 fatty acids such as flaxseed may have less benefit.

LDL (Low-Density Lipoproteins)

The LDL circulate 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.

Some fats in the diet are essential for good health, but others can be harmful. For this reason, recommendations focus both on the quantity and the quality of the fat in the diet. The current American diet delivers excessive amounts of solid fats, representing an average of almost one-fifth of the day's total kcalories. Major sources of solid fats in the American diet include desserts, pizza, cheese, and processed and fatty meats (sausages, hot dogs, bacon, ribs). Because foods made with solid fats provide abundant energy, but few if any essential nutrients, they contribute to weight gain and make it difficult to meet nutrient needs. Solid fats also provide abundant saturated fat and trans fat. Even without overweight or obesity, high intakes of solid fats increase the risk of some chronic diseases. One strategy to control saturated fat, trans fat, and kcalories is to limit solid fats in the diet.

The blood lipid profile 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. Both the amounts and types of fat in the diet influence the risk for disease. - blood lipid profile: results of blood tests that reveal a person's total cholesterol, triglycerides, and various lipoproteins.

Summarize fat digestion, absorption, and transport.

The body makes special arrangements to digest and absorb lipids. It provides the emulsifier bile to make them accessible to the fat-digesting lipases that dismantle triglycerides, mostly to monoglycerides and fatty acids, for absorption by the intestinal cells. Four types of lipoproteins transport 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 contain mostly cholesterol; and HDL are the densest and are rich in protein. High LDL and low HDL indicate increased risk of heart disease. By clearing blood cholesterol and inhibiting inflammation, HDL have a protective effect.

Cancer 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. (Chapter 18 provides many more details about these risk factors and the development of cancer.) The relationship between dietary fat and the risk of cancer differs for various types of cancers. In the case of breast cancer, evidence has been weak and inconclusive. Some studies indicate an association between dietary fat and breast cancer; more convincing evidence indicates that body fatness contributes to the risk. In the case of colon cancer, limited evidence suggests a harmful association with foods containing animal fats.

The relationship between dietary fat and the risk of cancer differs for various types and combinations of fats as well. The increased risk in cancer from fat appears to be due primarily to saturated fats or dietary fat from meats (which is mostly saturated). Fat from milk or fish has not been implicated in cancer risk.

Be aware that the "% Daily Value" for fat is not the same as "% kcalories from fat." This important distinction is explained in How To 5-3. Because recommendations apply to average daily intakes rather than individual food items, updated food labels will no longer provide "% kcalories from fat." Still, you can get an idea of whether a particular food is high or low in fat.

They may appear similar, but their difference is worth understanding. Consider, for example, a piece of lemon meringue pie that provides 140 kcalories and 12 grams of fat. Because the Daily Value for fat is 78 grams for a 2000-kcalorie intake, 12 grams represent about 18 percent:

solid shortening and margarine are made from vegetable oil that has been hardened through hydrogenation. This process both saturates some of the unsaturated fatty acids and introduces trans-fatty acids. Many convenience foods contain trans fats, including: Fried foods such as french fries, chicken, and other commercially fried foods Commercial baked goods such as cakes, pie crusts, frozen pizzas, biscuits, muffins, cookies, doughnuts, pastries, breads, and crackers Snack foods such as chips Imitation cheeses

To keep trans-fat intake low, use these foods sparingly.

Which of the following is not a function of adipose tissue?

To regulate blood glucose levels

functions of adipose tissue

To store fat To insulate the body from temperature extremes To protect vital organs from shock to secrete proteins that help regulate energy balance

Storing Fat as Fat - When meals deliver more energy than the body needs, the excess is stored as fat in the adipose cells for later use. As Figure 5-18 shows, triglycerides fill the adipose cells, storing a lot of energy in a relatively small space. This accumulation of fat in adipose tissue represents a key advantage that allows humans to survive through times when food is unavailable.

Using Fat for Energy - After meals, the blood delivers chylomicrons and VLDL loaded with triglycerides to the body's cells. An enzyme—lipoprotein lipase (LPL)—hydrolyzes those triglycerides, releasing fatty acids, diglycerides, and monoglycerides into the cells for energy. Fat supplies about 60 percent of the body's ongoing energy needs during rest. During prolonged light to moderately intense exercise, fat may make a slightly greater contribution to energy needs (see Photo 5-4). As exercise intensity increases, fat contributes less (and carbohydrate contributes more) to the fuel mix. - lipoprotein lipase (LPL): an enzyme that hydrolyzes triglycerides passing by in the bloodstream and directs their parts into the cells, where they can be metabolized for energy or reassembled for storage.

Milk and Milk Products Like meats, milk and milk products should also be selected with an awareness of their saturated fat contents (see Table 5-8). Keep in mind that the fat in milk is considered a solid fat; it is apparent as butter, but less so when suspended in homogenized milk. Fat-free and low-fat milk products provide as much or more protein, calcium, and other nutrients as their whole-milk versions—but with little or no saturated fat. Selecting fermented milk products, such as yogurt, may also help to lower blood cholesterol. These foods increase the population and activity of bacteria in the colon that use cholesterol. Interestingly, cheese does not seem to raise LDL cholesterol as its saturated fat content might predict, perhaps because its calcium promotes fat excretion in the GI tract. Such findings serve as a reminder to focus more on foods and eating patterns than on individual nutrients.

Vegetables, Fruits, and Grains Most vegetables and fruits naturally contain little or no fat. Although avocados and olives are exceptions, most of their fat is unsaturated, which is not harmful to heart health; in fact, avocados can significantly improve blood lipids as can olives and their oils. Most grains contain only small amounts of fat. Consumers need to read food labels carefully, though, because many refined grain products such as fried taco shells, croissants, and biscuits are high in saturated fat, and pastries, crackers, and cookies may contain trans fats. Similarly, many people add butter, margarine, or cheese sauce to grains and vegetables, which raises the saturated- and trans-fat contents. Because fruits are often eaten without added fat, a diet that includes several servings of fruit daily can help a person meet the dietary recommendations for fat. A diet rich in vegetables, fruits, whole grains, and legumes also offers abundant vitamin C, folate, vitamin A, vitamin E, and dietary fiber—all important in supporting health. Consequently, such a diet protects against disease by reducing saturated fat as well as by increasing nutrients. It also provides valuable phytochemicals, which help defend against heart disease.

monounsaturated fatty acid

a fatty acid that lacks two hydrogen atoms and has one double bond between carbons; abbreviated MUFA. Examples include palmitoleic acid and oleic acid. A monounsaturated fat is composed of triglycerides in which most of the fatty acids are monounsaturated. mono = one

Choline

a nitrogen-containing compound found in foods and made in the body from the amino acid methionine. Choline is part of the phospholipid lecithin and the neurotransmitter acetylcholine.

The following factors help lower LDL and/or raise HDL:

Weight control Monounsaturated or polyunsaturated, instead of saturated, fat in the diet Soluble dietary fibers Phytochemicals Moderate alcohol consumption Physical activity - Not too surprisingly, numerous genes influence how the body handles the synthesis, transport, and degradation of lipids and lipoproteins. Much current research is focused on how nutrient-gene interactions may direct the progression of heart disease.

The major sources of saturated fats in the US diet are fatty meats, whole milk, tropical oils, and products made from any of these foods. To limit saturated fat intake, consumers must choose carefully among these high-fat foods. More than a third of the fat in most meats is saturated. Similarly, more than half of the fat is saturated in whole milk and other high-fat milk products, such as cheese, butter, cream, half-and-half, cream cheese, sour cream, and ice cream. The tropical oils of palm, palm kernel, and coconut, which are rarely used by consumers in the kitchen, are used heavily by food manufacturers, and are commonly found in many commercially prepared foods.

When choosing meats, milk products, and commercially prepared foods, look for those lowest in saturated fat. Labels help consumers to compare products. Even with careful selections, a nutritionally adequate diet will provide some saturated fat. Zero saturated fat is not possible even when experts design menus with the mission to keep saturated fat as low as possible. Because most saturated fats come from animal foods, vegetarian diets can, and usually do, deliver fewer saturated fats than mixed diets.

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 and leaving a bond between the two molecules

Emulsifier

a compound with both water-soluble and fat-soluble portions that can attract fats and oils into water, combining them.

The emulsification of fat by bile is often compared to ________.

a detergent removing grease spots from clothes

unsaturated fatty acid

a fatty acid that lacks hydrogen atoms and has at least one double bond between carbons (includes monounsaturated and polyunsaturated fatty acids). An unsaturated fat is composed of triglycerides in which most of the fatty acids are unsaturated.

Hydrophilic

a term referring to water-loving, or water-soluble, substances.

Adipose tissue is more than just a storage depot for fat. 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. Researchers are currently exploring how adipokines influence the links between obesity and chronic diseases such as type 2 diabetes, hypertension, and heart disease. Obesity, for example, increases the release of the adipokine resistin that promotes inflammation and insulin resistance—factors associated with heart disease and diabetes. Similarly, obesity decreases the release of the adipokine adiponectin that protects against inflammation, diabetes, and heart disease. Fat serves other roles in the body as well. Because fat is a poor conductor of heat, the layer of fat beneath the skin insulates the body from temperature extremes. Fat pads also serve as natural shock absorbers, providing a cushion for the bones and vital organs. Fat provides the structural material for cell membranes and participates in cell signaling pathways.

adipokines: proteins synthesized and secreted by adipose cells. resistin: a protein produced by adipose cells that promotes inflammation and causes insulin resistance. adiponectin: a protein produced by adipose cells that inhibits inflammation and protects against insulin resistance, type 2 diabetes, and cardiovascular disease.

the type of fat may be more important than the

amount of fat

Linoleic acid is an essential fatty acid and 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. Should a linoleic acid deficiency develop, arachidonic acid, and all other omega-6 fatty acids that derive from linoleic acid, would also become essential and have to be obtained from the diet. A nonessential nutrient (such as arachidonic acid) that must be supplied by the diet in special circumstances (as in a linoleic acid deficiency) is considered a conditionally essential nutrient. Normally, vegetable oils and meats supply enough omega-6 fatty acids to meet the body's needs.

arachidonic acid: 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. conditionally essential nutrient: a nutrient that is normally nonessential, but must be supplied by the diet in special circumstances when the need for it exceeds the body's ability to make it.

Fill in the missing columns by matching the food choice with the type of fat.

avocado: monounsaturated cheddar cheese: saturated coconut oil: saturated canola oil: monounsaturated - Saturated fat is the predominant fat in coconut oil (~82%) and cheddar cheese (~63%), whereas monounsaturated fat is the predominant fat in avocado and canola oil.

Most often, a fat is partially hydrogenated, and some of the double bonds that remain after processing change their configuration from

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

Many vitally important body compounds are sterols. Among them are bile acids, the sex hormones (such as testosterone, androgen, and estrogen), the adrenal hormones (such as cortisol, cortisone, and aldosterone), 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. Unlike fatty acids, cholesterol cannot be used for energy.

endogenous: from within the body. exogenous: from outside the body. plaque: an accumulation of fatty deposits, smooth muscle cells, and fibrous connective tissue that develops in the artery walls in atherosclerosis. Plaque associated with atherosclerosis is known as atheromatous plaque. atherosclerosis: a type of artery disease characterized by plaques (accumulations of lipid-containing material) on the inner walls of the arteries.

triglycerides—either from food or from the body's fat stores—provide the cells with

energy

Recall that gram for gram, fat provides more than twice as much energy (9 kcalories) as carbohydrate or protein (4 kcalories), making it an extremely efficient storage form of

energy - the body's fat stores have virtually unlimited capacity, thanks to the special cells of the adipose tissue (the body's fat tissue; consists of masses of triglyceride-storing cells.)

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 and are therefore essential fatty acids. The cells do not possess the enzymes to make any of the omega-6 or omega-3 fatty acids from scratch, nor can they convert an omega-6 fatty acid to an omega-3 fatty acid or vice versa. Cells can, however, use the 18-carbon member of an omega family from the diet to make the longer fatty acids of that family by forming double bonds (desaturation) and lengthening the chain two carbons at a time (elongation). This is a slow process because the omega-3 and omega-6 families compete for the same enzymes. Too much of a fatty acid from one family can create a deficiency of the other family's longer fatty acids, which becomes critical only when the diet fails to deliver adequate supplies. Therefore, the most effective way to maintain body supplies of all the omega-6 and omega-3 fatty acids is to obtain them directly from foods—most notably, from vegetable oils, seeds, nuts, fish, and other seafoods.

essential fatty acids: fatty acids that the body requires but cannot make, and so must be obtained from the diet; both linoleic acid and linolenic acid are essential fatty acids.

Some foods are made with fat replacers—ingredients that provide some of the taste and texture of fats, but with fewer kcalories. Because the body may digest and absorb some of these fat replacers, they may contribute energy, although significantly less energy than fat's 9 kcalories per gram. Some fat replacers are derived from carbohydrate, protein, or fat. Carbohydrate-based fat replacers are used primarily as thickeners or stabilizers in foods such as soups and salad dressings. Protein-based fat replacers provide a creamy feeling in the mouth and are often used in foods such as ice creams and yogurts. Fat-based replacers act as emulsifiers and are heat stable, making them most versatile in shortenings used in cake mixes and cookies.

fat replacers: ingredients that replace some or all of the functions of fat and may or may not provide energy.

Which of these protein foods is the leanest?

flounder

A triglyceride consists of three fatty acids attached to a

glycerol -A triglyceride contains a molecule of glycerol with three fatty acids attached. Each carbon in glycerol is attached to a fatty acid. Cholesterol contains a four-ring carbon structure with one carbon side chain.

Phospholipids

have chemical structures that allow them to be soluble in both water and fat, a feature that allows them to form the lipid bilayer of the plasma membrane of a cell. Sterols are multiple-ringed structures that include cholesterol and steroid hormones.

The liver makes HDL (high-density lipoproteins) to remove cholesterol from the cells and carry it back to the liver for recycling or disposal. By efficiently clearing cholesterol, HDL help prevent plaque buildup, thereby lowering 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.

high-density lipoproteins: lipoproteins that help remove cholesterol from the blood by transporting it to the liver for reuse or disposal.

the degree of unsaturation

influences the firmness of fats at room temp - most polyunsaturated vegetable oils are liquid at room temperature, and the more saturated animal fats are solid. Some oils—notably, cocoa butter, palm oil, palm kernel oil, and coconut oil—are saturated; they are firmer than most vegetable oils because of their saturation, but softer than most animal fats because of their shorter carbon chains (8 to 14 carbons long). Generally, the shorter the carbon chain, the softer the fat is at room temperature.

The blood lipid profile reveals the concentration of various lipids in the blood. A desirable level of total cholesterol is

less than 200 mg/dL

a fourth 18-carbon fatty acid

linolenic acid - has three double bonds - essential fatty acid

Each day, the GI tract receives, on average from the food we eat, 50 to 100 grams of triglycerides, 4 to 8 grams of phospholipids, and 200 to 350 milligrams of cholesterol. These lipids are hydrophobic, whereas the digestive enzymes are hydrophilic. As you read, notice how the body elegantly meets the challenges of keeping the lipids mixed in the watery fluids of the GI tract and facilitating the work of the

lipases

The chylomicrons are one of several clusters of lipids and proteins that are used as transport vehicles for fats. As a group, these vehicles are known as lipoproteins, and they solve the body's challenge of transporting fat through the watery bloodstream. The body makes four main types of lipoproteins, distinguished by their size and density. Each type of lipoprotein contains different kinds and amounts of lipids and proteins. The more lipids, the less dense; the more proteins, the more dense

lipoproteins: clusters of lipids associated with proteins that serve as transport vehicles for lipids in the lymph and blood.

Fatty acids differ not only in the length of their chains and their degree of saturation, but also in the

locations of their double bonds

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 (see the inside front cover for details). The DRI suggest that linoleic acid provide 5 to 10 percent of the daily energy intake and linolenic acid 0.6 to 1.2 percent. No DRI have been established for the

long-chain omega-3 fatty acids EPA or DHA. - EPA: - DHA:

In the body, lipids provide energy, insulate against temperature extremes, protect against shock, and maintain cell

membranes

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

micelles: tiny spherical complexes of emulsified fat that arise during digestion; most contain bile salts and the products of lipid digestion, including fatty acids, monoglycerides, and cholesterol.

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.

monoglycerides: molecules of glycerol with one fatty acid attached. A molecule of glycerol with two fatty acids attached is a diglyceride.

The Dietary Guidelines recommend replacing saturated fats with

monounsaturated and polyunsaturated fats.

a relatively small amount of trans-fat in the diet comes from

natural sources - At current levels of consumption, natural trans fats have little, if any, effect on blood lipids. Some naturally occurring trans-fatty acids, known as conjugated linoleic acids, may even have health benefits. Conjugated linoleic acids are not counted as trans fats on food labels.

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 - the last letter of the Greek alphabet (ω), used by chemists to refer to the position of the closest double bond to the methyl end of a fatty acid.

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

omega-3 fatty acid

Regular consumption of ________ may help prevent blood clots.

omega-3 fatty acids

Cancer The omega-3 fatty acids of fatty fish may protect against some cancers as well, perhaps by suppressing inflammation. Even when omega-3 fats do not protect against cancer development, there seems to be a significant reduction in cancer-related deaths. Thus, dietary advice to reduce cancer risks parallels that given to reduce heart disease risks: reduce saturated fats and increase omega-3 fatty acids. Evidence does not support

omega-3 supplementation

Lecithin

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

Cholesterol

one of the sterols containing a four-ring carbon structure with a carbon side chain.

Omega-3 Supplements Omega-3 fatty acids are available in capsules of fish oil supplements, although routine supplementation is not recommended. High intakes of omega-3 polyunsaturated fatty acids may increase bleeding time, interfere with wound healing, raise LDL cholesterol, and suppress immune function. Such findings reinforce the concept that too much of a good thing can sometimes be harmful. People with heart disease, however, may benefit from doses greater than can be achieved through diet alone. This paradox reminds us that dietary advice to lower the risk of heart disease may differ from dietary advice to treat patients with heart disease. Because high intakes of omega-3 fatty acids can cause excessive bleeding, supplements should be used

only under close medical supervision

Cell membrane is made of

phospholipids assembled into a lipid bilayer - A phospholipid is similar in structure to a triglyceride, but only has two fatty acids and a phosphate compound attached to the glycerol backbone. The glycerol and phosphate heads are soluble in water, whereas the fatty acid tails are soluble in fat. A phospholipid bilayer is an ideal structure for a cell membrane, which must co-exist in watery fluids both outside and inside the cell. The phosphate heads form the outer and inside edges of the membrane, and the fatty acid tails associate with each other in the middle of the membrane. A membrane made up only of triglycerides could not co-exist in watery fluids to be functional.

conjugated linoleic 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).

are the following saturated or unsaturated? solid at room temp hydrogenated liquid at room temp

solid at room temp: saturated hydrogenated: saturated liquid at room temp: unsaturated - The degree of unsaturation influences the firmness of fats at room temperature. Fats containing high amounts of saturated fatty acids tend to be solid at room temperature because the saturated fatty acids stack together. Unsaturated fatty acids do not stack neatly because the double bond causes the fatty acid to bend. Thus, foods high in unsaturated fats tend to be liquid at room temperature.

Research on the different types of fats has spotlighted the many beneficial effects of the omega-3 polyunsaturated fatty acids. Regular consumption of omega-3 fatty acids may help 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 lower the incidence of heart disease-related deaths, support a healthy immune system, and

suppress inflammation

Triglycerides

the chief form of fat in the diet and the major storage form of fat in the body; composed of a molecule of glycerol with three fatty acids attached; also called triacylglycerols (try-ay-seel-GLISS-er-ols). - lipids composed of three fatty acids attached to a glycerol

point of unsaturation

the double bond of a fatty acid, where hydrogen atoms can easily be added to the structure

In nature, most double bonds are cis—meaning that the hydrogens next to the double bonds are on the same side of the carbon chain. Only a few fatty acids (notably a small percentage of those found in milk and meat products) naturally occur as...

trans-fatty acids - (meaning that the hydrogens next to the double bonds are on opposite sides of the carbon chain)

A saturated fatty acid contains ______ double bonds within the fatty acid chain, whereas an unsaturated fatty acid contains ______ double bonds

zero; one or more - A saturated fatty acid contains only single bonds between its carbon atoms because every carbon between the methyl and acid ends is holding the maximum number of hydrogen atoms, which is two. An unsaturated fatty acid contains one or more double bonds. Whenever a hydrogen is missing from two adjacent carbons in a chain, a double bond is formed so that each carbon in the chain is linked to four atoms. Carbon has a valence of four, requiring it to bond to 4 atoms, but two of those bonds could be to the same other atom.