human nutrition assignment | Applied Sciences homework help

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Source: Centers for Disease Control. 2017. Leading Causes of Death. Available at www.cdc.gov. TABLE 1.3 Leading Causes of Death in the United States M01_BLAK8260_04_SE_C01.indd 17 12/1/17 9:48 PM 18 Chapter 1 | What Is Nutrition? resist chronic disease. Variants alone rarely cause disease directly; usually, they increase the risk that the disease will develop given a conducive environment. The interactions between genes and your environment are complex. Scientific advances point to a variety of mechanisms by which nutrition—a key aspect of the cellular environment—inter- acts with genes to influence your risk of disease. While you can’t change the genetic cards you are dealt, by improving the quality of your diet, you can change the way you play the game. The Human Genome Project (HGP) mapped the sequence of all of the genes (the genome) in humans. Completion of the HGP has enabled nutritionists, geneticists, and other researchers to actively examine the synergistic effects of nutrition and genetics. This reaction either increases or decreases gene expression, producing greater or smaller amounts of proteins, which in turn affects body function. The study of the mechanisms by which factors such as food intake alter gene expression without changing the DNA sequence is known as epigenetics. For exam- ple, folate, one of the B vitamins, may alter the expression of genes as the embryo develops during early pregnancy. A deficiency of folate during this critical time increases the risk of specific birth defects in the baby. We talk more about this in Chapter 10. Until recently, nutrition research and genetic research contributed separately to our understanding of human health and disease. Studied together, these two fields help us understand how genetic variations influence an individual’s response to his or her diet (nutrigenetics), and how nutrients and other components of foods influence genetic expres- sion (nutritional genomics, or nutrigenomics). Recent advances in nutritional genomics have already yielded potential clinical appli- cations. For example, research has shown that chronic inflammation can be reduced with consumption of certain bioactive compounds found in food. These compounds include vitamin C in fruits and vegetables, vitamin E in wheat germ and vegetable oils,32 and the omega-3 fatty acids in fish.33 Increasing dietary intake of these compounds may regulate the expression of genes coding for proteins active in inflammation. Nutritional genomics may have tremendous potential to provide personalized dietary recommendations based on an individual’s genetic makeup. Ultimately, a future regis- tered dietitian nutritionist (RDN) may be able to use this information to recommend dietary modifications specific to a patient’s DNA. gene expression Processing of genetic information to create a specific protein. epigenetics Study of the variety of environmental factors and other mechanisms influencing gene expression. nutritional genomics Study of the relationship between genes, gene expression, and nutrition. registered dietitian nutritionist (RDN) Health professional who is a food and nutrition expert; RDNs obtain a college degree in nutrition from an Academy of Nutrition and Dietetics–accredited program and pass a national exam. ▲ Figure 1.5 Chronic Disease Is a Mixture of Genetic Influences and Our Environment Environmental influences Diet Physical activity Gene variants Susceptibility genes Chronic Disease The study of nutritional genomics may one day allow individuals to tailor their diets to their DNA. LO 1.5: THE TAKE-HOME MESSAGE Eating a balanced diet that includes ade- quate but not excessive amounts of all nutrients is the best way to stay healthy and reduce the risk of developing four of the top 10 leading causes of death in the United States, including heart disease, cancer, stroke, and diabetes. A healthy diet also prevents nutrient-deficiency diseases such as scurvy. In addi- tion, a healthy diet influences gene expression in ways that may increase or decrease your risk of disease. How Do We Assess Nutritional Status? LO 1.6 Summarize the ABCD method used to assess the nutrient status of individuals and populations. How do you know if you are eating enough of the essential nutrients? If you suspect you may not be meeting all of your nutrient needs, or you have been diagnosed with a nutrition-related disease, turn to a nutrition professional, such as an RDN. The RDN will M01_BLAK8260_04_SE_C01.indd 18 12/1/17 9:48 PM How Do We Assess Nutritional Status? 19 conduct a complete assessment to find out if you are getting too much, too little, or the right amount of all nutrients. Nutrition professionals describe a person’s state of nutrition as either healthy or malnourished. Someone who lacks a specific nutrient, or isn’t consuming enough energy, is undernourished, which means that person is at risk of losing too much weight or devel- oping a disease related to a nutrient deficiency. In contrast, an individual who overconsumes a particular nutrient, or eats too many kilocalories, is described as being overnourished. This person runs the risk of becoming overweight, developing diseases such as diabetes or heart disease, or potentially accumulating toxic amounts of a specific nutrient in the body. The ABCD Method Is Used to Assess the Nutritional Status of Individuals Evaluating a person’s current nutrition status begins with a look at that person’s health history, including any experiences with acute or chronic illness, and diagnostic proce- dures, therapies, or treatments that may increase nutrient needs or induce malabsorption. Does the patient have a family history of diabetes or heart disease? Has the patient been overweight or underweight in the past? To learn more about evaluating your own family history, see the Self-Assessment. malnourished Characterized by an inappropriate level of essential nutrients to maintain health; overnourishment and undernourishment are forms of malnutrition. undernourished Characterized by an inadequate energy intake or a deficiency in quality or quantity of one or more individual nutrients. overnourished Characterized by an excessive intake of energy or one or more individual nutrients. acute Characterized by a sudden onset and rapid progression of symptoms. malabsorption Condition characterized by impaired absorption of nutrients through the gastrointestinal tract. Along with the health history, nutrition professionals use a number of specialized methods to assess the nutritional status of individuals. You can use the mnemonic ABCD to help you remember these methods, which include collecting anthropometric data, collecting biochemical (laboratory) data, conducting a clinical exam, and performing dietary intake assessments ( Table 1.4). ABCD is more of a framework than a chronological guideline. Each portion builds off the other, but it is not necessary to conduct the method in any specific order. Assessing Dietary Intake through Questionnaires and Interviews Questioning an individual about his or her dietary intake and diet history is an important aspect of a nutrition assessment. A detailed diet history is conducted by a skilled inter- viewer who knows just what types of questions to ask to help a patient remember not only current food intake but food intake in the past. Two tools used to collect dietary intake data are questionnaires and interviews. Food frequency questionnaires and food records can be used to gather information about how often a specific food or category of food is eaten. A nutrition interview can reveal data about lifestyle habits, such as how many meals are eaten daily, where they are eaten, and who prepares them. Self-Assessment How Healthy Is Your Family Tree? You inherited your DNA from your parents, so the extent to which DNA affects health is largely hereditary. Does your family have a history of heart disease, diabetes, or obesity? What about other chronic diseases or conditions? Before you learn about the role that healthy eating plays in preventing chronic diseases, ask your parents and grandparents about your family’s health history. If there are certain diseases or conditions that run in your family, you’ll want to pay particular attention to these as you learn more throughout this text. An easy way to gather information about your family’s health history is by visiting My Family Health Portrait at http://familyhistory.hhs.gov. The site generates a family tree report according to the medical history you enter. Save a copy of the report for future reference. M01_BLAK8260_04_SE_C01.indd 19 12/1/17 9:48 PM 20 Chapter 1 | What Is Nutrition? weight, as well as how a child’s height and weight compare with others of the same age. All of these measurements are easily obtained with a scale and tape measure. The BMI is a measure of weight relative to height, and waist circumference measures abdominal fat. Body composition measurements can provide data on an individual’s lean body tissue and percentage of body fat. The measurements can be assessed with special- ized equipment, such as skin calipers or the Bod Pod. (We discuss these measurements in greater detail in Chapter 14.) Data collected from anthropometric measurements is then compared with reference standards. Patterns and trends become evident when more than one measurement is taken over time and compared with the initial values. By combining the results of the BMI and waist circumference with other information gathered during the nutrition assessment, an individual’s risk of developing diseases associated with obesity, such as diabetes and heart disease, can be determined. Conducting a Clinical Examination A person who is malnourished will exhibit physical symptoms as the body adjusts to the lack or excess of nutrients. Therefore, several parts of the body can be inspected during a clinical exam for evidence of malnutrition. Observing the hair, skin, eyes, fingernails, tongue, and lips can provide clues that point to under- or overnutrition. For example, cracks at the corners of the mouth can be evidence of B-vitamin deficiencies, whereas small pinpoint hemorrhages on the skin may reflect a deficiency of vitamin C. Observations of physical symptoms should be followed up by more direct measurements, including laboratory assessments. Collecting Biochemical Data Laboratory tests based on body fluids, including blood and urine, can be important indicators of nutritional status, but they are also influenced by non-nutritional factors. Biochemical tests of urine assess nutritional status by measuring, for example, how fast a nutrient is excreted through the urine and the metabolic by-products of various nutrients found in urine. Blood tests may measure levels of albumin (a blood protein) to screen for protein deficiency; low hemoglobin levels in the blood indicate iron-deficiency anemia; and a high fasting blood sugar level may suggest diabetes. Surveys Are Used to Assess the Nutritional Status of a Population Group Assessing the nutritional status of an individual in a clinical setting is one thing, but how do we determine the nutritional status of a population? What percentage of Americans is meeting the dietary recommendations for healthy eating? To find out, researchers col- lect dietary intake information on a large scale. The information is used by researchers in many ways, such as to determine the adequacy of the current nutrient recommendations for different population groups, to evaluate and develop food assistance programs, and to assess risk of nutritional deficiencies. Populations are typically assessed through the use of surveys. Numerous national surveys have been developed by a variety of federal agencies to assess the health and nutritional status of Americans. The National Health and Nutrition Examination Survey (NHANES) is one of the most prominent. Conducted annually, it is used to determine the nutritional status of Americans of all ages and to monitor their risk behaviors over time. The intake of carbohydrates, lipids, protein, vitamins, minerals, and fiber is collected using a 24-hour recall method and reported in the document What We Eat in America. The Framingham Heart Study, which coined the term risk factors, had a major impact on the dietary intake of Americans. This study used surveys to collect longitudinal data on two generations and more than 10,000 participants to establish the current recommenda- tions for the prevention of cardiovascular disease. body mass index (BMI) Measurement calculated using the metric formula of weight in kilograms divided by height in meters squared; used to determine whether an individual is underweight, at a healthy weight, overweight, or obese. One of the easiest ways to determine an individual’s intake of nutrients is to use the food frequency questionnaire (FFQ). This form of assessment provides evidence of consump- tion patterns over time. For example, if you wanted to determine the usual calcium intake over time of an older woman with osteoporosis, an FFQ could be used to indicate the number of servings of dairy foods “per day, per week, and per month,” as well as whether she “seldom” or “never” consumes milk, cheese, or yogurt. The FFQ is a reasonably reli- able, accurate, and inexpensive method to assess usual intake.34 This assessment tool is not as helpful in assessing the actual amount consumed of a nutrient, nor does it always accurately reveal usual intake. For that information, a food record or 24-hour dietary recall usually provides a better picture.35 A food record is simply a diary of what foods and beverages are eaten, how much, and when they are eaten over a defined period of time. Food records are often kept for 3–7 days and are considered by some to be one of the best methods for collecting diet information. There are drawbacks to this method. The accuracy depends on the individual’s skill and com- mitment to keeping a valid record. Many people start out strong and then lose interest or simply forget to record the food. Or, they might alter their usual food intake to avoid feeling embarrassed about what they eat. Food records can be kept in written form, such as a journal, or with an electronic diet analysis program. There are also new digital and mobile devices that may help improve the accuracy, ease, and evaluation of recording dietary intake.36 The FFQ or a diet record should be selected based on the specific information the assessor needs to know, such as iron intake over time and how much iron the individual eats daily, as well as the assessor’s ability to complete the instrument accurately. The information obtained from these tools is then compared with current dietary standards, which we discuss in the next chapter. The 24-hour dietary recall method is a quick assessment conducted by a trained interviewer who asks a patient to recall all the food and drinks, including snacks, eaten the previous day. This tool relies on the skills of the interviewer and the individual’s ability to remember what he or she ate and drank the day before. Because dietary intake varies from one day to the next, one 24-hour period may not provide an accurate estimate of typical intake. Collecting Anthropometric Data Data about body size or body composition is also called anthropometric data. In adults, this usually means height, weight, body mass index (BMI), waist-to-hip ratios, and waist circumference. For children, growth charts have been developed that compare height to Type of Assessment Measurements What They Determine Anthropometric Height Weight Body mass index Waist-to-hip ratio Waist circumference Growth, obesity, changes in weight, and risk of developing chronic diseases such as diabetes and heart disease Biochemical Blood, urine, and feces Protein, mineral, and vitamin status and disease Clinical Observe hair, fingernails, skin, lips, mouth, muscles, joints, overall appearance Signs of deficiencies and excesses of nutrients Dietary Intake Diet history Diet record Food frequency questionnaire 24-hour dietary recall Usual nutrient intake and deficiencies or excesses of various nutrients TABLE 1.4 The ABCDs of Nutrition Assessment Whether a handwritten log or a smartphone app, food diaries can be useful tools for assessing nutritional status. M01_BLAK8260_04_SE_C01.indd 20 12/1/17 9:48 PM How Do We Assess Nutritional Status? 21 weight, as well as how a child’s height and weight compare with others of the same age. All of these measurements are easily obtained with a scale and tape measure. The BMI is a measure of weight relative to height, and waist circumference measures abdominal fat. Body composition measurements can provide data on an individual’s lean body tissue and percentage of body fat. The measurements can be assessed with special- ized equipment, such as skin calipers or the Bod Pod. (We discuss these measurements in greater detail in Chapter 14.) Data collected from anthropometric measurements is then compared with reference standards. Patterns and trends become evident when more than one measurement is taken over time and compared with the initial values. By combining the results of the BMI and waist circumference with other information gathered during the nutrition assessment, an individual’s risk of developing diseases associated with obesity, such as diabetes and heart disease, can be determined. Conducting a Clinical Examination A person who is malnourished will exhibit physical symptoms as the body adjusts to the lack or excess of nutrients. Therefore, several parts of the body can be inspected during a clinical exam for evidence of malnutrition. Observing the hair, skin, eyes, fingernails, tongue, and lips can provide clues that point to under- or overnutrition. For example, cracks at the corners of the mouth can be evidence of B-vitamin deficiencies, whereas small pinpoint hemorrhages on the skin may reflect a deficiency of vitamin C. Observations of physical symptoms should be followed up by more direct measurements, including laboratory assessments. Collecting Biochemical Data Laboratory tests based on body fluids, including blood and urine, can be important indicators of nutritional status, but they are also influenced by non-nutritional factors. Biochemical tests of urine assess nutritional status by measuring, for example, how fast a nutrient is excreted through the urine and the metabolic by-products of various nutrients found in urine. Blood tests may measure levels of albumin (a blood protein) to screen for protein deficiency; low hemoglobin levels in the blood indicate iron-deficiency anemia; and a high fasting blood sugar level may suggest diabetes. Surveys Are Used to Assess the Nutritional Status of a Population Group Assessing the nutritional status of an individual in a clinical setting is one thing, but how do we determine the nutritional status of a population? What percentage of Americans is meeting the dietary recommendations for healthy eating? To find out, researchers col- lect dietary intake information on a large scale. The information is used by researchers in many ways, such as to determine the adequacy of the current nutrient recommendations for different population groups, to evaluate and develop food assistance programs, and to assess risk of nutritional deficiencies. Populations are typically assessed through the use of surveys. Numerous national surveys have been developed by a variety of federal agencies to assess the health and nutritional status of Americans. The National Health and Nutrition Examination Survey (NHANES) is one of the most prominent. Conducted annually, it is used to determine the nutritional status of Americans of all ages and to monitor their risk behaviors over time. The intake of carbohydrates, lipids, protein, vitamins, minerals, and fiber is collected using a 24-hour recall method and reported in the document What We Eat in America. The Framingham Heart Study, which coined the term risk factors, had a major impact on the dietary intake of Americans. This study used surveys to collect longitudinal data on two generations and more than 10,000 participants to establish the current recommenda- tions for the prevention of cardiovascular disease. body mass index (BMI) Measurement calculated using the metric formula of weight in kilograms divided by height in meters squared; used to determine whether an individual is underweight, at a healthy weight, overweight, or obese. M01_BLAK8260_04_SE_C01.indd 21 12/1/17 9:48 PM 22 Chapter 1 | What Is Nutrition? How Healthy Is the Average American Diet? LO 1.7 Discuss the current nutritional state of the average American diet. The food supply in the United States provides an array of nutritious choices to meet the dietary needs of Americans. Fresh fruits and vegetables, whole grains, lean meats, fish, and poultry are easily accessible and affordable through local grocery stores and farmers markets. With such an abundance of healthy foods to choose from, are Americans adopt- ing healthy diets? The Quality of the American Diet Needs Improvement In general, the American diet is too high in added sugars, sodium, and saturated fat.37 Added sugars account for 13 percent of America’s daily kilocalories. This is largely due to Americans’ love of soft drinks, other sugary beverages, and sweets and treats.38 High sodium intake is a risk factor for hypertension, and Americans consume far more than is recommended. The American diet also contains too much saturated fat, the form of fat linked to cardiovascular disease. Whereas the recommended intake is to consume less than 10 percent of your total daily kilocalories from saturated fat, Americans, on average, are consuming over 11 percent. However, most Americans don’t exceed the recommended dietary cholesterol intake limit of 300 milligrams per day.39 In contrast, our intake of fiber and certain vitamins and minerals is too low.40 Our low fiber intake is partly due to inadequate consumption of fruits and vegetables and overconsumption of refined grains, which provide far less fiber than whole grains. (The role of dietary fiber in health is discussed in Chapter 4.) American women fail to meet their recommended intake for iron, and Americans in general don’t consume enough vitamin D, potassium, and calcium.41 In an attempt to balance their poor choice in foods, over 50 percent of Americans take at least one vitamin or mineral supplement per day.42 Our lack of a healthy diet may be due in part to where we eat and with whom we eat. Today, many Americans eat most of their meals away from home.43 Some of us eat in the car or buy takeout meals or prepared foods from the supermarket. Research suggests that increasing the number of meals consumed as a family may improve the dietary quality of the entire family. Eating family meals together seven or more times per week has been associated with consuming an additional serving of both fruits and vegetables daily as compared with families who do not dine together.44 The majority of Americans understand the positive benefits of eating breakfast, yet nearly 25 percent of Americans skip this morning meal.45 Breakfast, which often includes foods from the dairy, grains, and fruit groups, is an important meal that could provide Americans with fiber (whole-grain cereal), vitamin D and calcium (milk), and potassium added sugars Sugars added to foods during processing and/or packaging. LO 1.6: THE TAKE-HOME MESSAGE An individual’s nutritional status is assessed by gathering information from health history, dietary record, and anthropometric, clinical, and biochemical (laboratory) data. When the information from the ABCD methods is viewed together, a comprehensive picture of the individual’s nutritional status can be determined. The National Health and Nutrition Examination Survey is used to determine the nutritional status of a large population. The Framingham Heart Study provided the foundation for the current dietary recommendations for heart health. M01_BLAK8260_04_SE_C01.indd 22 12/1/17 9:48 PM How Healthy Is the Average American Diet? 23 (bananas, orange juice). Many Americans are falling short of fiber and these three nutrients in their daily diet. Rates of Overweight and Obesity in Americans Are Too High As Americans take in more kilocalories than they burn in their sedentary lives, they create a recipe for overweight and obesity. Overall, more than 35 percent of American adults are obese.46 Rates within certain populations and geographical regions are even higher (Figure 1.6). Along with these increases in obesity have come higher rates of type 2 diabetes, particularly among children, and increased rates of heart disease, cancer, and stroke. Reducing America’s obesity rate is therefore a top public health priority. Healthy People 2020 Provides Health Objectives for Americans The U.S. Surgeon General has issued calls for a nationwide health improvement program since 1979. The latest edition of this report, Healthy People 2020, contains a set of health objectives for the nation to achieve over the second decade of the twenty-first century.47 There are more than 35 topic areas in Healthy People 2020, rang- ing from ensuring that Americans have adequate access to health services to improvements in their diet and physical activity. Objec- tives are developed within each topic area. For example, research indicates that Americans’ body weights are increasing rather than decreasing. Thus, “Nutrition and Weight Status” is one topic area. The numerous objectives developed within this topic area, if ful- filled, will help Americans improve their diet and reduce their weight and their risk for chronic disease. Table 1.5 lists a few objec- tives in this topic area. As you can see from the table, consuming adequate amounts of fruits and vegetables is beneficial to managing one’s weight. Americans should increase their intake of both of these food sources to help them improve their nutrition and weight status. ▲ Figure 1.6 Obesity Trends Among U.S. Adults Over the past few decades, rates of obesity have risen significantly in the United States. Source: Centers for Disease Control. 2016. “Prevalence of Self-Reported Obesity among U.S. Adults.” Available at www.cdc.gov. a b Objectives Target for Americans (%) Status of Americans (%) Increase the proportion of adults who are at a healthy weight 33.9 30.8 Reduce the proportion of adults who are obese 30.5 33.9 Reduce the proportion of children and adolescents ages 2–19 who are considered obese 14.5 16.1 Increase the contribution of fruits to diets of the population age 2 years and older 0.9 cups/1,000 kcals 0.5 cups/1,000 kcals Increase the variety and contribution of vegetables to the diets of the population age 2 years and older 1.1 cups/1,000 kcals 0.8 cups/1,000 kcals Source: United States Department of Health and Human Services. Nutrition and Weight Status: Objectives. Updated January 12, 2017. Healthy People 2020. Available at www.HealthyPeople.gov. Accessed January 2017. TABLE 1.5 Healthy People 2020 Nutrition and Weight Status Objectives M01_BLAK8260_04_SE_C01.indd 23 12/1/17 9:48 PM 24 Chapter 1 | What Is Nutrition? What Is Credible Nutrition Research? LO 1.8 Describe the scientific method that leads to reliable and accurate nutrition information. If you Google the word nutrition, you will get a list of about 14.5 million entries in 0.25 sec- onds. Obviously, the world is full of nutrition information at our fingertips. But is it credible? Anyone who has attempted to lose weight can probably tell you how hard it is to keep up with the latest diet advice—because it seems to keep changing. In the 1970s, waist watchers were told that carbohydrates were the bane of their existence and that a protein-rich, low-carbohydrate diet was the key to shrinking their waistline. A decade later, avoiding fat was the way to win the battle of the bulge. By 2000, carbohydrates were being ousted again, and protein-rich diets were back in vogue. More recently, high-protein diets have been losing popularity and high-carbo- hydrate diets are once again being promoted for weight loss. So . . . are you frustrated yet? Whereas diet trends and popular wisdom seem to change fre- quently, basic scientific knowledge about nutrition does not. Results from individual studies are often deemed newsworthy and publicized in the media, but the results of one report do not radically change expert opinion. Only when multiple, affirming research studies have been con- ducted is a consensus reached about nutrition advice. News of the results of one study is just that: news. In contrast, advice from an author- itative health organization or committee, such as the American Heart Association or the Dietary Guidelines Advisory Committee, which is based on a consensus of research infor- mation, is sound information that can be trusted for the long term. Sound Nutrition Research Begins with the Scientific Method Sound research studies begin with a process called the scientific method. Scientists observe something in the natural world, ask questions, and propose an explanation (or hypothesis) based on their observations. They then test their hypothesis by conducting an experiment. There are many steps in the scientific method and many adjustments are made along the way before a scientist has gained enough information to draw a conclusion about his or her hypothesis. In fact, the entire process can take years to complete. Let’s walk through a nutrition-related study in which scientists used the scientific method to study rickets (Figure 1.7). Rickets is a disease in children in which the leg bones are so weakened that they cannot hold up the child’s body weight. The legs bow as a result. In the early 1800s, parents often used cod-liver oil to treat rickets because it seemed to provide a miraculous cure. consensus Agreed-upon conclusion of a group of experts based on a collection of information. scientific method Process used by scientists to gather and test information for the sake of generating sound research findings. hypothesis Idea or explanation proposed by scientists based on observations or known facts. LO 1.7: THE TAKE-HOME MESSAGE The American diet is too high in added sugars, sodium, and saturated fat, and too low in dietary fiber, vitamin D, potassium, and calcium. Rates of overweight and obesity among Americans are too high. Incidences of overweight and obesity among Americans are prevalent, yet many people are falling short of some nutrient needs. Healthy People 2020 is a set of health objectives for the nation to achieve over the second decade of the twenty-first century. Nutrition-related stories often lead in newspa- pers and magazines and on websites. M01_BLAK8260_04_SE_C01.indd 24 12/1/17 9:48 PM What Is Credible Nutrition Research? 25 Scientists noticed the cod-liver oil curing phenomenon and asked themselves why cod-liver oil cured rickets. In doing so, these scientists were using the first step in the scientific method: observing and asking questions. The second step of the scientific method is to formulate a hypothesis. Because cod- liver oil is very rich in vitamin A, scientists initially thought that this vitamin was the curative factor. To confirm this, scientists proceeded to the third step, which was to conduct an experiment. The scientists altered the cod-liver oil to destroy its vitamin A. The altered oil was given to rats that had been fed a diet that caused rickets. Surprisingly, the rats were still cured of rickets. This disproved the scientists’ original hypothesis that vitamin A was the curative factor. They then needed to modify their hypothesis, as it was obvious that there was something else in the cod-liver oil that cured rickets. They next hypothesized that it was the vitamin D in the oil that cured the rats. They conducted another experiment to confirm this hypothesis, which it did. What good would it be to make such an important discovery if other scientists couldn’t find out about it? Fortunately, scientists today share their findings by summarizing and submitting their research to a peer-reviewed journal (Figure 1.8). Other scientists (peers) review the researchers’ findings to make sure that they are sound. If so, the research study is published in the journal. After that, it may be picked up by the popular press and reported. If the relationship between vitamin D and rickets were discovered today, it would probably be the lead story on CNN. As more and more studies confirmed that vitamin D could cure and prevent rickets, a theory developed. By the 1920s, researchers knew with great certainty that vitamin D prevents rickets, and that a deficiency of vitamin D can cause deformed bones in children. Because of this, there is a consensus among health professionals as to the importance of vitamin D in the diets of children. peer-reviewed journal Journal in which scientists publish research findings, after the findings have gone through a rigorous review process by other scientists. ◀ Figure 1.7 Steps of the Scientific Method The scientific method is used to conduct credible research in nutrition and other scientific fields. Observe and ask a question Why does cod-liver oil cure rickets? Hypothesis supported Rats were not cured. Hypothesis not supported Rats were cured. Revise or formulate a new hypothesis Conduct an experiment Feed rats with rickets cod-liver oil that contains no vitamin A. Formulate a hypothesis The vitamin A in cod-liver oil is the curative factor. ▲ Figure 1.8 A Hypothesis Can Lead to a Scientific Consensus When a hypothesis is supported by research, the results are published in peer-reviewed journals. Once a theory has been developed and supported by subsequent experiments, a consensus is reached in the scientific community. Hypothesis supported Publish findings Develop theory Establish consensus M01_BLAK8260_04_SE_C01.indd 25 12/1/17 9:48 PM 26 Chapter 1 | What Is Nutrition? Scientists Use a Variety of Experiments to Test Hypotheses Scientists can use different types of experiments to test a hypothesis. A laboratory exper- iment is done within the confines of a lab setting, such as the rickets experiments with rats. Research conducted with humans is usually observational or experimental. Observational research involves exploring factors in two or more groups of sub- jects to see if there is a relationship to a certain disease or health outcome. One type of observational research is epidemiological research, which looks at health and disease in populations of people. For example, scientists may notice that there is a higher incidence of rickets among children who live in Norway than among children who live in Australia. Through their observations, they may find a relationship between the lack of sun exposure in Norway and the high incidence of rickets there compared with sunny Australia. How- ever, the scientists can’t rule out that the difference in the incidence of rickets in these two populations may also be due to other factors in the subjects’ diet or lifestyle. This type of research does not answer the question of whether one factor directly causes another. Experimental research involves at least two groups of subjects. One group, the experimental group, is given a treatment, and another group, the control group, isn’t. When scientists hypothesized that vitamin D cured rickets, they would have randomly assigned children with rickets to one of two groups (Figure 1.9). The scientists would have laboratory experiment Scientific experiment conducted in a laboratory; some involve animals. observational research Research that involves systematically observing subjects to see if there is a relationship to certain outcomes. epidemiological research Research that studies the variables that influence health in a population; it is often observational. experimental research Research involving at least two groups of subjects receiving different treatments. experimental group In experimental research, the group of participants given a specific treatment, such as a drug, as part of the study. control group In experimental research, the group that does not receive the treatment but may be given a placebo instead; used as a standard for comparison. ▶ Figure 1.9 Controlled Scientific Experiments Scientists use experimental research to test hypotheses. Select a large number of subjects with rickets. Randomly divide subjects into two groups. To prevent bias, neither the subjects nor the scientists know which group receives what treatment. Compare results. Did the vitamin D cure rickets in the experimental group and did the control group remain unchanged? Experimental group receives vitamin D supplement. Control group receives placebo. Vitamin D cures rickets Yes No Revise hypothesis M01_BLAK8260_04_SE_C01.indd 26 12/1/17 9:48 PM What Is Credible Nutrition Research? 27 given the experimental group a vitamin D supplement but would have given the control group a placebo, which looked just like the vitamin D supplement but contained only sugar. If neither of the two groups of subjects knew which pill they received, then the subjects were “blind” to the treatment. If the scientists who gave the placebo and the vitamin D supplement also didn’t know which group received which treatment, the exper- iment would be called a double-blind placebo-controlled study. The scientists would also have to make sure that the variables were the same or controlled for both groups during the experiment. For example, they couldn’t let the control group go outside in the sunshine and at the same time keep the experimental group of subjects inside, since sun- light is known to allow humans to synthesize vitamin D. The exposure to the sunshine would change the outcome of the experiment. A double-blind placebo-controlled study is considered the “gold standard” of research because all of the variables are the same and controlled for the groups of subjects and nei- ther the subjects nor the researcher are biased toward one group. In any scientific research, sample sizes must be large enough to ensure that differ- ences found in the study are due to the treatment rather than to chance. Studying an entire population is usually impossible because the population is too large, the study would be too expensive or time-consuming, or all members of the population do not want to par- ticipate. This was the case with the vitamin D and rickets study mentioned earlier. It would be virtually impossible to measure all children with rickets. Instead, a sample of children with rickets was used and a statistical comparison was done to estimate the effects on the population. Generally, the larger the sample size, the more confident the researchers are that the data reflects reliable differences that would most likely be seen in the population. The beauty of science is that one discovery builds on another. Though this may seem frustrating when the findings of one research study contradict the results of another from just a few months before, conflicting findings actually help scientists formulate new ques- tions. Though many hypotheses fail along the way, a great many discoveries are also made. placebo Inactive substance, such as a sugar pill, administered to a control group during an experiment. double-blind placebo-controlled study Experimental study in which neither the researchers nor the subjects in the study are aware of who is receiving the treatment or the placebo. LO 1.8: THE TAKE-HOME MESSAGE Sound nutrition advice is based on years of research using the scientific method. Several methods can be used to con- duct nutrition research, including laboratory experiments on animals, experi- mental research on humans, and observational, particularly epidemiological, research. In double-blind placebo-controlled studies, neither the subject

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