You should pack foods high in ________ to provide the most energy or kilocalories per gram of food.

3

1 Learning Outcomes After reading this chapter, you will be able to:

1.1 Discuss the factors that drive our food choices.

1.2 Define the term nutrition and characterize nutrients.

1.3 Explain the primary roles of the six classes of nutrients found in food.

1.4 Describe the best approach to meeting your nutritional needs.

1.5 Summarize three ways in which diet influences health.

1.6 Summarize the ABCD method used to assess the nutrient status of individuals and populations.

1.7 Discuss the current nutritional state of the average American diet.

1.8 Describe the scientific method that leads to reliable and accurate nutrition information.

1.9 Explain how to identify reliable nutrition infor- mation and how to recognize misinformation.

True or False? 1. Food choices are driven primarily by flavor. T/F 2. Nutrition is the study of dietary

supplements. T/F 3. Carbohydrates provide our main source of energy. T/F 4. Alcohol is a nutrient. T/F 5. Taking a dietary supplement is the only way to meet your nutrient needs. T/F 6. The most effective method of nutritional assessment is to ask clients to write down what they’ve eaten in the last 24 hours. T/F 7. About 25 percent of all Americans are obese. T/F 8. Eliminating all fat from the diet will

reduce your risk of developing heart disease. T/F 9. Cancer is the leading cause of death in the United States. T/F

10. You can get good nutrition advice from anyone who calls him- or herself a nutritionist. T/F See page 36 for the answers.

What Is Nutrition?

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4 Chapter 1 | What Is Nutrition?

What Drives Our Food Choices? LO 1.1 Discuss the factors that drive our food choices.

Have you ever considered what drives your food choices? Or are you on autopilot as you stand in line at the sub shop and squint at yet another menu board? Do you enjoy some foods and eat them often, while avoiding others with a vengeance? You obviously need food to survive, but beyond your basic instinct to eat are many other factors that affect your food choices. These factors include taste and enjoyment; culture and environment; social life and trends; nutrition knowledge; advertising; time, convenience, and cost; and habits and emotions (Figure 1.1).

Taste and Enjoyment Research confirms that when it comes to making food choices, taste is the most important consideration.2,3 This shouldn’t be too much of a surprise, considering there are more than 10,000 taste buds in the mouth. These taste buds tell you that chocolate cheesecake is sweet, fresh lemon juice is sour, and a pretzel is salty. Our preferences for sweet, salty, or creamy foods may be inf luenced by our genes4 and may change as we age.5

We have a taste for fat, which may also be genetically linked.6 When fat is combined with sugar, such as in a sugar-laden doughnut, our preference for that food is even stronger.7

Texture also affects our likelihood of enjoying foods. We enjoy a f laky piecrust but dislike one that is tough; we prefer crunchy apples to mealy ones, and creamy rather than lumpy soups. Almost 30 percent of adults dislike slippery foods, such as oysters and okra.8 Researchers have suggested that people’s preferences for sweetness, high fat, and specific textures begin early in life and this makes them resistant to change.9▲ Figure 1.1 Many Factors Influence Your Food Choices

Food Choices

Advertising Social reasons

Convenience

Emotions

Time

Habits

Culture

Nutrients

Cost

Taste

TrendsNutrition knowledge

During the course of a day, we make over 200 decisions about food, from when to eat, how much to eat, and what to eat, to how the food is prepared, and even what size plate to use.1 You make these decisions for reasons you may not even be aware of. If your dietary advice comes from media sound

bites, you may receive conflicting information. Last week’s news flash announced that eating more pro-

tein would help you fight a bulging waist. Yesterday’s headline boldly announced that limiting sugary

drinks was the key. This morning, the TV news lead was a health report on the weight-loss benefits of

consuming more dietary fiber.

It can be frustrating when nutrition news seems to change daily, but the research behind this barrage

of news illustrates the progress nutrition scientists are making toward understanding what we eat and

how it affects our health. Today’s research validates what nutrition professionals have known for decades:

Nutrition plays an invaluable role in your health.

In addition to exploring the factors that affect food choice, this chapter introduces you to the study

of nutrition. Let’s begin with the basic concepts of why and what you eat, why a healthy diet is important

to your well-being, and how you can identify credible sources of nutrition information.

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What Drives Our Food Choices? 5

Culture and Environment Enjoying food is not just a physiological sensation. Other factors, such as our culture and the environment, also play a role in which foods we eat.10 If you were a student in Mexico, you may regularly feast on corn tortillas and tamales, as corn is a staple of Mexican cuisines. In India, meals commonly include lentils with rice and vegetables, whereas Native Americans often enjoy stews of mutton (sheep), corn, vegetables, and berries. And, in Asian countries, rice likely would be front and center on your plate.

The environment in which its people live significantly influences a culture’s cuisine. This includes the climate and soil conditions as well as the native plants and animals and the distance people live from rivers, lakes, or the ocean. Foods that are available and acces- sible are more likely to be regularly consumed than foods that are scarce. For example, native Alaskans feast on fish because it is plentiful, but eat less fresh produce, which is difficult to grow locally. For most Americans today, global food distribution networks have made eating only locally available foods less of an issue than in the past; however, the tendency persists for some food items.

Our food environment—the variety of food choices available, the size and shape of plates and glassware, the packaging of foods, and the types and amounts of food that are visible—has a strong influence on what and how much we consume. We eat more food when the serving plates are larger and drink less when beverages are served in taller glasses. Environmental cues also affect eating patterns. You are more likely to linger over a meal when the light is dimmed,11 or quickly finish your meal when you are standing rather than sitting. Physical cues, such as a friend’s empty appetizer plate covered with disposed-of cocktail sticks, may signal you to eat more of your appetizer.

Social Life and Trends Every year on the fourth Thursday in November, approximately 48 million turkeys are consumed when Americans gather with family and friends to celebrate Thanksgiving.12 A person is likely to eat more on Thanksgiving than on any other Thursday, and this is partly because of the number of people eating with them. Eating dinner with others has been shown to increase the size of the meal by over 40 percent, and the more people present at the meal, the more you’ll eat.13

Eating is an important way to bond with others. Sharing a meal with family or friends stimulates conversation, creates traditions, and expands our food experiences. Although eat- ing a quick meal in the campus cafeteria may not provide you the most healthy food options, it will allow you to socialize with classmates.

For many people, activities such as watching a football game with fellow fans or going to a movie with friends often involve particular foods. More pizzas are sold on Super Bowl Sunday than on any other day of the year.14 Movie theater owners bank on their patrons buying popcorn, candy, and beverages at the concession stand before heading in to watch the film.15

Food choices are also affected by popular trends. For instance, home cooks in the 1950s bought bags of “newfangled” frozen vegetables in order to provide healthy meals in less time. A few decades later, vegetables went upscale and consumers bought them as part of ready-to-heat stir-fry mixes. Today, shoppers pay a premium for bags of fresh veggies, like carrots, that have been prewashed and peeled, sliced, or diced, and they pay even more if the food is labeled “organic.” In 2013 alone, Americans spent more than $35 billion on organic foods.16 Millennials (people born between about 1980 and 2000) who are parents are the biggest group of consumers buying organic foods.

Roughly one in three Americans is of Hispanic, Native American, Asian, or African descent. Cultural food preferences often influence food choices.

Eating junk food while watching sports or attending a sporting event sometimes seems like an American way of life.

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6 Chapter 1 | What Is Nutrition?

Food sustainability and food waste are also topics that are on the radar of restaurant patrons and shoppers, who may choose vegetarian meals or smaller portions out of concerns for the environment. Supermarkets provide dozens of choices in flavored and enhanced bottled teas and waters, which are trendy beverages among college students. As food manufacturers pour more money into research and development, who knows what tomorrow’s trendy foods will be?

Nutrition Knowledge Individuals may choose certain foods they associate with good health or avoid other foods they associate with poor health. For example, many Americans consume vegetables, fruits, and whole

grains because they perceive them as healthy choices that can help them control their blood pressure or reduce their risk of colon cancer.17 At the same time, many Americans worry about fried foods causing heart disease.

When it comes to weight management, some consumers believe that specific dietary components are the culprits behind weight gain. While 3 in 10 consumers believe that overeating any type of food will cause weight gain, one in four believe that sugar is more likely to cause you to pack on the pounds.18

The more aware you are of the effects of food choices on health, the more likely you are to make an effort to improve those choices. If you believe that choosing low-sodium foods will decrease your blood pressure or that eating yogurt with active cultures will improve your digestion, you are more likely to choose these foods. Many consumers are label-reading in the supermarket, checking the expiration date, Nutrition Facts panel, and ingredients list before buying a food product.19

Advertising The food and beverage industry spends over $136 million annually on advertising.20 Food companies spend these large sums on advertising for one reason: It works, especially on young people. American children view an estimated 30 hours of food commercials on the television annually, and more than half of these advertisements are for unhealthy foods.21

In contrast, commercials for fruits and vegetables are rare, which is unfortunate because healthy foods can be successfully marketed. The Fruit and Vegetable (FNV) campaign, the brainchild of the Partnership for a Healthier America (PHA), a nonprofit organization working with public, private, and nonprofit leaders to develop strategies to end childhood obesity, knows that celebrity marketing to kids is powerful. They recruited influential actors and athletes, all pro bono, to get kids to chow down more produce. Their research showed that 70 percent of individuals who were aware of FNV stated that they purchased and ate more fruits and vegetables after seeing or hearing about the campaign.22

Time, Convenience, and Cost When it comes to making a meal, time is often at a premium. A recent survey reported that close to 60 percent of Millennials spend as little as 15 minutes cooking dinner during the week.23 Consequently, supermarkets are now offering more prepared and partially prepared foods. If chicken is on the menu tonight, you can buy it uncooked at the meat counter in the supermarket, or you can go to the deli and buy it hot off the rotisserie, cooked and stuffed with bread crumbs or grilled with teriyaki sauce. Rice or pasta side dishes and cooked vegetables are also available to complete the meal.

The USDA certifies that foods labeled “organic” are grown without the use of toxic and persistent pesticides or fertilizers.

Rates of fruit and vegetable consumption increased among consumers exposed to the FNV advertising campaign.

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What Is Nutrition? 7

Convenience has also become more of a factor in food selection. Foods that are easily accessible to you are more likely to be eaten. Decades ago, the most convenient way to get a hot cup of coffee was to brew it at home. Today, Americans are more likely to get their latte or half-caff from one of the 29,000 coffee shops across the United States.24

For reasons related to both time and convenience, people eat out more often today than they did a few decades ago. In the 1970s, Americans spent less of their household budget on eating out, compared with today.25 Because cost is often an issue when con- sidering where to eat out, most meals consumed away from home are fast food, which is often cheaper and quicker than more nutritious meals. Though cheap fast food may be easy on the pocketbook, it is taking its toll on the health of Americans. Epidemiological research suggests that low-cost, high-calorie diets, such as those that incorporate lots of burgers, fries, tacos, and soft drinks, increase the risk of obesity, especially among those at lower socioeconomic levels.26

The good news is that cheaper food doesn’t have to always mean fast food, and when healthy foods are offered at lower prices, people do buy them. More Americans, especially urban Millennials, are opting for boxes of fresh fruits and vegetables or meal kits delivered directly to their door. They may eat home-cooked meals more often because of these services.27

Researchers have found that lowering the cost of fresh fruits and vegetables improves the consumption of these nutritious foods.28 This suggests that price reductions are an effective strategy to increase the purchase of more-healthful foods.

Habits and Emotions Your daily routine and habits often affect both when you eat and what you eat. For exam- ple, if you routinely start your day with a bowl of cereal, you’re not alone. Ready-to-eat cereals are the number-one breakfast food choice among Americans.29 Many individuals habitually snack when watching television or sitting at the computer.30

For some individuals, emotions can sometimes drive food choice: feeling happy or sad can trigger eating. In some cases, appetite is suppressed during periods of sadness or depression; in others, food is used as an emotional crutch during times of stress, depres- sion, or joy.

Although brown rice is a healthy whole-grain addition to any meal, it generally takes almost an hour to cook. For time-strapped consumers, food manufacturers have developed brown rice that cooks in 10 minutes and a precooked, microwavable variety that reheats in less than 2 minutes.

LO 1.1: THE TAKE-HOME MESSAGE Taste and enjoyment are the primary rea- sons people prefer certain foods. A food’s availability makes it more easily become part of a culture, and many foods can be regularly eaten out of habit. Advertising, food trends, limited time, convenience, emotions, and the percep- tion that foods are healthy or unhealthy also influence food choices.

What Is Nutrition? LO 1.2 Define the term nutrition and characterize nutrients.

The science of nutrition is the study of food and the nutrients we need to sustain life and reproduce. It examines the way food nourishes the body and affects health. Since its incep- tion, the science of nutrition has explored how food is digested, absorbed, transported, metabolized, and used or stored in the body. Nutritional scientists study how much we need of each nutrient, the factors that influence our needs, and what happens if we don’t consume enough. As with any science, nutrition is not stagnant. The more we discover about the relationship between nutrition and well-being, the greater the impact will be on long-term health.

nutrition Science that studies how nutrients and other components of foods nourish the body and affect body functions and overall health.

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8 Chapter 1 | What Is Nutrition?

Nutrients Are Essential Compounds in Food The body is one large organism made up of millions of cells that grow, age, reproduce, and die, all without your noticing. You slough off millions of skin cells when you towel off after a shower, yet your skin isn’t noticeably thinner today than it was last week. Your body replaces skin cells at a rate fast enough to keep you covered, and it manufactures new cells using the same nutrients found in a variety of foods. As cells die, nutrients from food provide the building blocks to replace them. Nutrients also provide the energy we need to perform all body functions and processes, from maintaining heartbeat to playing tennis.

There are six categories of nutrients found in foods and in the body: carbohydrates, lipids (fats), protein, vitamins, minerals, and water. Foods also often contain beneficial non-nutrient compounds, such as phytochemicals or zoochemicals, and nondigestible fiber, as well as chemicals added by food manufacturers to enhance color, flavor, or tex- ture or extend shelf-life.

Plant foods are made up of about 10 percent carbohydrates, fats, proteins, vitamins, and minerals (Figure 1.2). The rest is typically water, and plant foods contain more water (about 90 percent) than do animal foods (about 70 percent). Animal foods are composed of about 30 percent protein, lipids, vitamins, and minerals. One unique quality of animal foods, with the exception of dairy products, is that they do not contain any carbohydrates by the time we consume them.

A healthy human body is about 60 percent water. The other 40 percent is made up of protein and fat, as well as a small amount of stored carbohydrates, minerals in bone, and small amounts of vitamins. Thus, the old saying is true that we are what we eat, from the carbohydrates in broccoli to the proteins in meat. The six biochemical ingredients needed to sustain life are all provided by the foods in our diets.

In general, nutrients are essential—they must come from foods because either they cannot be made in the body at all, or they cannot be made in sufficient amounts to meet the body’s needs. The body can make a few nonessential nutrients in sufficient quanti- ties. An example is vitamin D, which is synthesized in the skin upon exposure to sunlight. Under some circumstances, nonessential nutrients can become essential. We refer to these nutrients as conditionally essential. If you are not exposed to enough sunlight, you will not be able to synthesize an adequate amount of vitamin D. You must then obtain vitamin D from foods and/or supplements.

Most Nutrients Are Organic Carbohydrates, proteins, lipids, and vitamins are the most complex of the six classes of nutrients. These nutrients are organic because their chemical structures contain carbon. Organic nutrients also contain the elements hydrogen and oxygen, and in the case of proteins and some vitamins, nitrogen is also part of the molecule (Figure 1.3).

Minerals are the least complex of the nutrients. From calcium to zinc, each mineral is an individual element, and its atoms are exactly the same whether found in food or in the body. For instance, the structure of zinc found in lean meats and nuts is the same as that found in a cell membrane or a hair follicle. Minerals are inorganic because, as individual elements, they do not contain carbon. Water, a three-atom molecule composed of hydrogen and oxygen, is also inorganic. The Chemistry Boost will help you visualize elements and molecules.

Some Nutrients Provide Energy All creatures need energy in order to function, and humans are no exception. Energy is defined as the capacity to do work. It also provides a source of heat. The body derives chemical energy from certain nutrients in foods, which store energy in their chemical

nutrients Compounds in foods that sustain body processes. There are six classes of nutrients: carbohydrates, fats (lipids), proteins, vitamins, minerals, and water.

essential nutrients Nutrients that must be consumed from foods because they cannot be made in the body in sufficient quantities to meet its needs and support health.

▲ Figure 1.2 Nutrients in Foods and in the Body Water is the most abundant nutrient found in foods and in the body. Carbohydrates, fats, protein, vitamins, and minerals make up the rest. Note that foods also contain non-nutritive compounds, such as phytochemicals and fiber.

Minerals

Minerals

Vitamins

Vitamins

Minerals Vitamins

Carbohydrates

Protein

Fat

Water

Human body

Protein

Fat

Water

Protein

Water

Carbohydrates

Chicken breast

59%

20%

17%

Broccoli (raw)

22%

74%

7%

89%

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What Is Nutrition? 9

bonds. During digestion and metabolism, the bonds are broken and the energy is released. This chemical energy released when the foods are digested can be converted into adenosine triphosphate (ATP), a form of energy the body can use. Carbohydrates, lipids (fats), and proteins are defined as the energy-yielding nutrients because they contribute energy to the body. Alcohol, although not a nutrient, also provides energy.

Scientists use the metric system to measure weight, volume, and distance. Grams are the fundamental units of measurement for weight; liters are the fundamental units for volume; and meters are the units used to measure distance. The metric system is a decimal system; that is, larger and smaller units are multiples or divisions of 100. For example, a kilogram is 1,000 grams (kilo = 1,000) and a centimeter is a hundredth of a meter (cent = 100). This uniform system of measurement allows scientists all over the world to share and compare data. Appendix B provides commonly used metric units.

Scientists measure the energy in foods in kilocalories. A kilocalorie is defined as the amount of energy needed to raise the temperature of one kilogram of water 1 degree

organic Describing compounds that contain carbon or carbon–carbon bonds.

nonessential nutrients Nutrients that can be made in sufficient quantities in the body to meet the body’s requirements and support health.

inorganic Describing elements or compounds that do not contain carbon.

energy Capacity to do work.

energy-yielding nutrients Three nutrients that provide energy to the body to fuel physio- logical functions: carbohydrates, lipids, and protein.

kilocalorie Amount of energy required to raise the temperature of 1 kilogram of water 1 degree centigrade; used to express the measurement of energy in foods; 1 kilocalorie is equal to 1,000 calories.

◀ Figure 1.3 The Chemical Composition of the Six Classifications of Nutrients in Food Each nutrient contains a unique combination of chemical elements.

Carbon

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

In or

ga ni

c O

rg an

ic

Hydrogen Oxygen Nitrogen Single elements

Some vitamins contain nitrogen

Carbohydrates

Lipids

Proteins

Vitamins

Minerals

Water

H ƒ

H ¬ C ¬ H ƒ

H

H ¬ O ¬ H

Methane (CH4) Water (H2O)

Chemical Bonds Most nutrients consist of carbon, hydrogen, and oxygen. These elements

combine to form compounds through chemical reactions. An atom of each element can carry a positive or negative charge and can form a set number of bonds with other elements. For example, carbon can form bonds with four elements, hydrogen can form one bond, and oxygen can form two bonds, as illustrated below. Two or more atoms bonded together are called molecules. Molecular oxygen, for example, contains two oxygen atoms (O2). Compounds are molecules containing two or more different elements. Water (H2O) is a compound. Molecules tend to be more stable than atoms, and, like atoms, can carry a positive or negative charge. Charged atoms or molecules are called ions.

Chemistry Boost

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10 Chapter 1 | What Is Nutrition?

Celsius. A kilocalorie is not the same as a calorie (with a lowercase c ), which is a much smaller unit of measurement. (In fact, a “calorie” is so small that one slice of bread con- tains about 63,000 calories.) One kilocalorie is equal to 1,000 calories.

To add to the confusion, the term Calorie (with an uppercase C ) is used on nutrition labels to express the energy content of foods and is often used in science textbooks to mean kilocalories. This text refers to the units of energy found in foods as kilocalories, abbreviated kcalories or kcals.

Each energy-yielding nutrient provides a set number of kilocalories per gram. Thus the number of kilocalories in one serving of a given food can be determined based on the amount (in grams) of carbohydrates, protein, and fat in the food. Carbohydrates and pro- tein provide 4 kilocalories per gram; so, for example, a food that contains 5 grams of car- bohydrate and 3 grams of protein would have 32 kilocalories ([5 * 4] + [3 * 4] = 32). Fats yield 9 kilocalories per gram, more than twice the number of kilocalories in either carbohydrates or protein. Alcohol contains 7 kilocalories per gram, which must be taken into account when calculating the energy of alcohol-containing foods and beverages (Figure 1.4).

Use the Calculation Corner to determine the number of kilocalories in a snack of potato chips and cola.

Energy in foods and in the body is trapped within the bonds that keep the mol- ecules together. When the bonds are broken during the process of metabolism, a sig- nificant amount of energy, including some heat, is released. The energy can then be used to digest and absorb the meal, contract muscles, fuel the heartbeat, synthesize new cells, and perform other functions. The Chemistry Boost will help you visualize covalent bonds.

People’s energy needs vary according to their age, gender, and activity level. Males generally need more energy because they weigh more and have more muscle mass (which

▶ Figure 1.4 The Energy-Yielding Nutrients and Alcohol Provide Kilocalories Carbohydrates, fats, and protein provide energy, or kilocalories, to fuel the body. Alcohol also contains kilocalories.

Carbohydrates 4 kcal/g

Alcohol 7 kcal/g

Fats 9 kcal/g

Protein 4 kcal/g

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What Is Nutrition? 11

Covalent Bonds A chemical reaction unites two atoms by creating a bond that forms a new

molecule. A covalent bond is formed when atoms share their electrons, as in the case of water. The oxygen atoms require two additional electrons and the hydrogen atoms need one electron to be stable. When these three atoms combine, the oxygen shares one electron with each of the hydrogen atoms and the hydrogen atoms share one electron with the oxygen atom. The atoms are held together because of their affinity to share each other’s electrons. The covalent bond that is formed is strong and difficult to break. Trapped within the bonds is stored energy that is released when the bonds are broken.

Chemistry Boost

O H

H

O

H H

Calculation Corner

Calculating Kilocalories in a Snack of Chips and Soda Suppose you ate an entire 8-ounce bag of potato chips and drank a 16-ounce cola while you studied for an exam. Together these two items contain 144 grams of carbohydrate (in the cola and chips), 12 grams of protein (from the chips), and 60 grams of fat (also in the chips). How many kilo- calories did you consume?

(a) To calculate the total kilocalories in this snack, multiply the total grams of each energy nutrient times the number of kilocalories per gram of that nutrient. Remember, a gram of carbohydrate and protein each contain 4 kilocalories and a gram of fat contains 9 kilocalories.

(144 g * 4 kcals/g) + (12 g * 4 kcals/g) + (60 g * 9 kcals/g) = 1,164 kcals 576 kcals + 48 kcals + 540 kcals = 1,164 kcals

In one sitting, you consumed more than 1,100 kilocalories, which for some people may be more than half of the amount they need to meet their daily energy requirement. If behaviors like this become habits, they can quickly result in weight gain.

(b) Another useful measure for assessing the nutritional quality of the snack is the percentage of fat, protein, and/or carbohydrate found in the food (you learn in later chapters that there are ranges for each nutrient that are considered part of a healthy diet). For example, what percentage of kilo- calories in the chips and soda is from fat? To answer this question, divide the fat kilocalories by the total kilocalories in the food and multiply by 100:

(540 kcals , 1,164 kcals) * 100 = 46, fat

Almost half of the kilocalories in this snack are from fat. Do you think this is likely to be a desirable proportion?

For practice, complete the same calculations for carbohydrate and protein.

Go to Mastering Nutrition and complete a Math Video activity similar to the problem in this Calculation Corner.

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12 Chapter 1 | What Is Nutrition?

requires more kilocalories to function) and less body fat. Younger people require more energy than older adults because they are still growing and therefore synthesizing more new tissue. Physically active individuals require more energy than sedentary people to fuel their activities and meet their body’s basic energy needs.

Energy that is not used to fuel the body will be stored, predominantly as fat, for later use. If you regularly consume more kilocalories than you expend, you will accumulate stored fat in adipose tissue and gain weight. The opposite is also true. Eating fewer kilo- calories than the body needs will result in the breakdown of stored energy and weight loss.

LO 1.2: THE TAKE-HOME MESSAGE Nutrition is the science of how nutrients and other components of foods nourish the body, and how the body uses nutrients to manufacture and replace cells and produce energy. Most nutrients are essential; that is, they cannot be synthesized in adequate amounts to meet body needs. Carbohydrates, lipids, proteins, and vitamins are organic nutrients composed of the chemical elements carbon, hydrogen, oxygen, and sometimes nitrogen. Minerals and water are inorganic because they don’t contain carbon. Energy in foods is measured in kilocalories. The energy-yielding nutrients—carbohydrates (4 kilocalories per gram), lipids (9 kilocalories per gram), and proteins (4 kilocalo- ries per gram)—provide fuel to be used by the body or stored for future use. Alcohol (7 kilocalories per gram) is not a nutrient but does provide energy.

Nutrient Provides Energy

Participates in Growth, Maintenance, Support, or Structure Regulates Body Processes

Macronutrients Carbohydrates Yes No No

Protein Yes Yes Yes

Fats Yes Yes Yes

Water No Yes Yes

Micronutrients Vitamins No Yes Yes

Minerals No Yes Yes

TABLE 1.1 Functions of the Major Nutrients by Type

Carbohydrates are found in a variety of foods, including breads, grains, and pasta.

What Are the Primary Roles of the Six Classes of Nutrients? LO 1.3 Explain the primary roles of the six classes of nutrients found in food.

Individual nutrients supply energy, regulate metabolism, and provide structure ( Table 1.1). Some nutrients, including carbohydrates, lipids, proteins, and water, are called macronu- trients (macro means “large”) because they are needed in much larger amounts to support normal functioning. Vitamins and minerals, though equally important to health, are con- sidered micronutrients (micro means “small”) because they are required in smaller amounts to perform their key roles. We introduce each of the six classifications of nutrients briefly in this chapter; they are discussed in much greater detail later in the textbook.

Carbohydrates Are the Primary Energy Source All forms of carbohydrates are composed of carbon (carbo-), hydrogen, and oxygen (hydrate means “water”). Carbohydrates supply simple sugar, called glucose, which is the primary source of energy for most body cells.

macronutrients Essential nutrients, including water and the energy-containing carbohydrates, lipids, and proteins that the body needs in large amounts.

micronutrients Essential nutrients the body needs in smaller amounts: vitamins and minerals.

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What Are the Primary Roles of the Six Classes of Nutrients? 13

Carbohydrates are found in most foods. Breads, cereals, nuts, fruits, legumes (dry beans, peas, and lentils), other vegetables, and dairy products are all rich in carbohydrates. The only foods that do not provide significant amounts of carbohydrates are animal products other than dairy, such as eggs, meat, poultry, and fish. (Chapter 4 covers carbohydrates in detail.)

Lipids Also Provide Energy The term lipid refers to a diverse group of organic compounds including fats (also called triglycerides), phospholipids, and sterols that are insoluble in water. These nutrients contain the same chemical elements as carbohydrates, including carbon, hydrogen, and oxygen. The difference is that lipids are much more concentrated than carbohydrates and contain less oxygen.

Triglycerides make up the majority of the lipids we eat and are found in margarine, butter, oils, and animal products. Triglycerides are an important energy source for the body, especially during rest and sleep. The body stores excess energy as triglycerides in the adipose tissue beneath the skin, which insulates the body and cushions the organs. (Chapter 5 presents more information on lipids.)

Proteins Provide the Building Blocks for Tissue Synthesis Proteins contribute the basic building blocks, known as amino acids, to synthesize, grow, and maintain tissues in the body. The tissues in muscles, bones, and skin are primarily made up of protein. Proteins also participate as neurotransmitters in the complex communication network between the brain and the rest of the body, and they play a role in the immune system and as enzymes that catalyze chemical reactions.

Proteins are similar in composition to carbohydrates and lipids in that they contain carbon, hydrogen, and oxygen. But proteins are unique in that they all contain the element nitrogen, and some also contain sulfur. Proteins can be used for energy but are usually not a primary energy source.

Protein is found in a variety of foods, including meats, dairy products, nuts, and seeds. Legumes such as soy also provide signifi- cant protein, and certain other vegetables, whole grains, and some fruits provide small amounts. (Chapter 6 covers protein in detail.)

Vitamins and Minerals Play Vital Roles in Metabolism Vitamins and minerals do not provide energy, but they are involved in numerous key functions in the body. They are essential to help regulate metabolism, for example, and without them we would be unable to convert carbohydrates, fats, and proteins to energy or to sustain numerous other chemical reactions. A deficiency of vitamins and minerals can cause a cascade of ill health effects ranging from fatigue to stunted growth, weak bones, and organ damage. The metabolic fate of carbohydrates, protein, and fats in the body depends on consuming enough vitamins and minerals in the daily diet.

Vitamins Many vitamins function as coenzymes; that is, they help enzymes catalyze reactions in the body. For example, the B vitamin thiamin attaches to and assists an enzyme involved in carbohydrate metabolism. Vitamins also activate enzymes that participate in building bone and muscle, energy production, fighting infections, and maintaining healthy nerves and vision.

There are 13 known vitamins, and each has a unique chemical structure. They are grouped into two classifications according to their solubility, which affects how they are

enzymes Proteins in living cells that act as catalysts and control chemical reactions.

coenzymes Substances, such as vitamins or minerals, that facilitate the activity of enzymes.

solubility Ability to dissolve into another substance.

Meats and dairy products are excellent sources of protein. Plant products, such as nuts, seeds, and legumes, also provide protein to the diet.

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14 Chapter 1 | What Is Nutrition?

A wide variety of fruits and vegetables are abundant sources of water-soluble vitamins.

absorbed, stored, and excreted. Water-soluble vitamins, which include vitamin C and the eight B-complex vitamins, are easily absorbed and excreted by the body and need to be consumed daily. The fat-soluble vitamins—A, D, E, and K—are stored in the liver and fatty tissues and thus don’t need to be consumed on a daily basis. (Vitamins are dis- cussed in Chapters 9 and 10.)

Minerals Minerals are inorganic elements that assist in body processes and are essential to the struc- ture of hard tissues, such as bone, and soft tissues, such as the red blood cells. Minerals like calcium and phosphorus work with protein-containing hormones and enzymes to maintain and strengthen teeth and bones. A deficiency of any of the minerals can cause disease symptoms. Falling short of daily iron needs, for example, can cause fatigue and impair your immunity.

Minerals are classified by the amount needed in the diet and total content found in the body. Major minerals are needed in amounts of at least 100 milligrams per day and are found in amounts of at least 5 grams in the body. Calcium and magnesium are two examples of major minerals. In addition to contributing to the structure of bones and teeth, some major minerals help maintain fluid balance, participate in energy meta- bolism, or contribute to muscle contractions. (Each individual major mineral is described in Chapter 12.)

Trace minerals are needed in amounts of less than 100 milligrams per day and are found in amounts of less than 5 grams in the body. Iron and zinc are two examples of trace minerals. Among other functions, trace minerals transport oxygen and carbon di oxide, participate in cell growth and development, control the metabolic rate, and play a role in body defenses. (Chapter 13 provides more specific detail on the role of trace minerals.)

Water Is Critical for Numerous Functions Some of the essential roles of water in the body probably seem obvious, as it makes up the majority of all body fluids, including digestive secretions, blood, urine, and perspi- ration. Less obvious is the fact that water is part of every cell in the body, from muscle and bone cells to brain and nerve cells. Water is also vital to several key body functions. It is essential during metabolism, for example, because it provides the medium in which metabolic reactions take place. Water functions in digestion and absorption and as a transport medium that delivers nutrients and oxygen to the cells through blood and lymph and excretes waste products through the urine and feces. Water helps maintain body temperature and acts as a lubricant for the joints, eyes, mouth, and intestinal tract. It surrounds vital organs and cushions them from injury. Because the body can’t store water, it must be replenished every day to maintain hydration. (The role of water in the body is discussed in Chapter 11.)water-soluble vitamins Vitamins that

dissolve in water; they generally cannot be stored in the body and must be consumed daily.

fat-soluble vitamins Vitamins that dissolve in fat and can be stored in the body.

major minerals Minerals found in the body in amounts greater than 5 grams; also referred to as macrominerals.

trace minerals Minerals found in the body in amounts less than 5 grams; also referred to as microminerals.

LO 1.3: THE TAKE-HOME MESSAGE The six classes of essential nutrients— carbohydrates, lipids (fats), protein, vitamins, minerals, and water—each have specific roles in the body. Carbohydrates and lipids are the body’s primary energy sources. Proteins can be used for energy, but their main role is to provide the building blocks for body structures and functional compounds. Vitamins, minerals, and water are needed to use the energy-producing nutri- ents and for various body processes.