Chapter 3 Nutrition and the Scientific Method

Learning Objectives

By the end of this chapter you will be able to:

• Describe the importance of research and scientific methods to understanding nutrition.
• Delineate the steps in the scientific method.
• Differentiate between types of scientific nutrition studies.
• Describe different types of scientific publications presenting nutrition data.

The Scientific Method

The discovery of chemicals and their roles in nutrition are examples of how the scientific method leads to new and useful information. Observations are the first steps of the scientific process. Scientists notice associations between eating habits, foods, and health issues. The next steps are to make an educated prediction about what is happening (formally called a hypothesis), to test this hypothesis, and to interpret the results. Finally, they gather additional evidence from multiple sources, discuss their finding with colleagues, come to a conclusion, and present their findings to others, usually in a written research report. This organized process of inquiry used in science is called the scientific method. This orderly presentation shows the core of the scientific process. However, actual scientific research can be less linear. Experiments lead to modification of hypotheses, which requires more experiments, which may generate entirely new questions and hypotheses, etc.

 

In 1811, French chemist Bernard Courtois was isolating saltpeter for producing gunpowder to be used by Napoleon’s army. To carry out this isolation, he burned some seaweed and, in the process, observed an intense violet vapor that crystallized when he exposed it to a cold surface. He sent the violet crystals to an expert on gases, Joseph Gay-Lussac, who identified the crystal as a new element. It was named iodine, the Greek word for violet. Below are examples of some of the studies which led to the conclusion that iodine is a nutrient with specific health benefits. Rest assured that experiments involving human subjects are carefully regulated in the modern era!

Example study 1:

• Observation. Eating seaweed is a cure for goiter, a gross enlargement of the thyroid gland in the neck.
• Hypothesis. In 1813, Swiss physician Jean-Francois Coindet hypothesized that the seaweed contained iodine, and that iodine could be used instead of seaweed to treat his patients^[1].
• Experimental test. Coindet administered iodine tincture orally to his patients with goiter.
• Data analysis. Administration of iodine successfully treated the goiters.
• Interpretation. Iodine is the component of seaweed that is effective in treating goiters.

Example study 2:

• Hypothesis. French chemist Chatin proposed that the low iodine content in food and water in certain areas far away from the ocean was the primary cause of goiter and renounced the theory that goiter was the result of poor hygiene.
• Experimental test. In the late 1860s the program, “the stamping-out of goiter,” started with people in several villages in France being given iodine tablets.
• Data analysis. Eighty percent of goitrous children who received iodine tablets were cured.
• Interpretation. Goiters arise because of a deficiency of iodine. Supplementation with iodine can cure the condition.

Example study 3:

• Hypothesis. In 1918, Swiss doctor Bayard proposed iodizing salt as a good way to treat people in areas in which goiter is common.
• Experimental test. Iodized salt was transported by mules to a small village at the base of the Matterhorn where more than 75 percent of school children were goitrous. Each family received salt containing one of three different concentrations of iodine. They used it in food preparation for six months.
• Data analysis. The prevalence of goiter among the children declined in all the groups.
• Interpretation. Even small amounts of iodine decrease the prevalence of goiter in children.

Example study 4:

• Hypothesis. School-age girls eating iodized salt will have less goiter than those who eat salt without iodine. Physician David Marine recruited volunteers among families in Akron, Ohio.
• Experimental test. Physician David Marine conducted the first American experiment of treating goiter with iodized salt in Akron, Ohio^[2]. Over 4000 girls participated (with parental consent). Some used iodized salt in home cooking and some did not.
• Data analysis. In the untreated groups, over 25% of the girls had goiter. In the treated group, only 0.2% had goiter.
• Interpretation. Addition of iodine to the diet through iodized salt is effective in reducing goiter in school-aged girls.
• Conclusions. These studies and others conducted in the US and in Europe demonstrated the effectiveness of iodized salt in treating goiter. Salt with iodine was first available in grocery stores in Switzerland in 1922, in Michigan in 1924, and throughout the US soon after. Today, more that 70% of American households use iodized salt, and many countries consider iodized salt an important part of their public health strategies. The incidence of goiter and another medical condition called congenital iodine deficiency syndrome have declined with the use of iodized salt.

Evidence-Based Approach to Nutrition

It took more than one hundred years from iodine’s discovery as an effective treatment for goiter until public health programs recognized it as such. Although a lengthy process, the scientific method is a productive way to define essential nutrients and determine their ability to promote health and prevent disease. The scientific method is part of the overall evidence-based approach to designing nutritional guidelines^[3]. An evidence-based approach to nutrition includes^[4]:

• Defining the problem or uncertainty (e.g., the incidence of goiter is lower in people who consume seaweed)
• Formulating it as a question or hypothesis (e.g., Does eating seaweed decrease the risk of goiter? Or There is a compound in seaweed that decreases the risk of goiter.)
• Setting criteria for quality evidence
• Evaluating the results of research studies
• Summarizing the body of evidence and making decisions
• Specifying the strength of the supporting evidence required to make decisions
• Disseminating the findings

In the U.S., the Food and Nutrition Board of the National Academy of Medicine (NAM; formerly called the Institute of Medicine, IoM), a nonprofit, non-governmental organization, constructs its nutrient recommendations (i.e., Dietary Reference Intakes, or DRI) using an evidence-based approach to nutrition. The procedure for setting the DRI is documented and available to the public^[5]. The same approach is used by the U.S. Department of Agriculture (USDA) and the U.S. Department of Health and Human Services (HHS). The USDA and HHS websites have multiple articles about nutrition and health (https://www.usda.gov/topics/food-and-nutrition and https://www.hhs.gov/programs/prevention-and-wellness/nutrition-and-fitness/index.html). Gathering information from multiple sources can be helpful. Differences in data interpretation can lead to different opinions even among experts. Comprehensive references for understanding how DRIs are produced are published by the National Academies of Sciences, Engineering and Medicine^{[6] and [7]}.

Types of Scientific Studies

Various types of studies are used to investigate researchers’ questions. Data from these studies may support a hypothesis or produce evidence that it is not true. Types of studies include observational studies and experimental studies with human subjects, animal studies, and studies that use cells or molecules in test tubes or dishes (in vitro studies). Each type has advantages and drawbacks, and each can provide different types of data.

Table 3.1 Types of Scientific Studies. Source: Human Nutrition, University of Hawai‘i at Mānoa Food Science and Human/CC BY 4.0.

Type	Description	Example	Notes
Observational studies	Studies which observe what people do and don’t ask people to change anything	Do people who eat a diet low in saturated fat have less cases of heart disease?	Can only indicate associations (correlation), not cause-and-effect relationship (causation). Might include something happening to people (such as measuring and weighing or taking a blood sample to analyze), but no treatment or intervention.
Experimental studies (also called Interventional studies)	Studies in which a variable is changed between two groups. Subjects receive a treatment that controls do not receive.	Do people who take a calcium supplement develop osteoporosis less often than those who take a placebo (pill that looks the same but does not contain calcium)?	Can indicate causation. Some studies are blinded, which means the subjects do not know if they are subjects or controls. Randomization of participants helps eliminate bias and influence of other factors.
Animal studies	Includes observational and experimental studies using animals as subjects	Does a new drug lower blood pressure in rats? In pigs?	Can give preliminary information about safety and efficacy, can be less expensive than human studies, can be more controlled than human studies (rats don’t go out for ice cream after dinner!). Ethical considerations are different (though still important) for animals.
In vitro studies	Studies using cells or molecules	Does the new drug cross a cell membrane efficiently?	Cannot indicate how something will affect an intact animal (including humans); widely used in developing treatments to determine safety and to learn how compounds act in cells.

Observational Studies

Observational studies may also be called epidemiological studies. In this type of study, the researcher is interested in a particular variable but does not control it. Subjects are exposed to a particular factor in the course of living their lives, and researchers observe the health or other characteristics of the people. Examples of factors that are studied in this way include smoking cigarettes, eating a high-fiber diet, and taking vitamin supplements, possibly over many years. The question that researchers are trying to answer is whether the factor is associated with an increased risk of a bad health outcome (such as heart disease) or possibly a good health outcome, such as stronger bones. Observational studies can be prospective or retrospective.

Prospective studies

In prospective studies, subjects are recruited and followed over time. Subjects are free of disease or symptoms at the beginning of the study; researchers monitor them for exposure to the factor as well as for the outcome to be measured, hoping to gain enough data to draw conclusions about a possible link between the factor and some health condition. The most common type of these studies is a cohort study. Subjects are recruited from a population and followed for a set amount of time.

For example, researchers might be interested in whether vitamin E intake is associated with the risk for Alzheimer’s disease (AD), a disease which may develop slowly over many decades. They could recruit a cohort of healthy people without AD, ask at regular intervals how much vitamin E they intake and whether they have developed any symptoms of the disease. You can see that these types of studies are complicated by reliance on people’s memory and honesty about answering questions about diet and health as well as by the need to keep the study going for many years.

Retrospective Studies

Retrospective studies are observational studies in which subjects are chosen because they already have a disease or other characteristic. Researchers ask them questions about their past exposure to the variable they are studying and try to draw conclusions about an association between exposure and disease development. The most common type of retrospective study is a case-control study. The subjects who have the disease are called the cases. For each case, the researchers find a person who does not have the disease but otherwise matches in important ways such as age, sex, location, even lifestyle, profession, education, etc. These matching but healthy people are called controls. The two groups are compared to determine if they have to a suspected intervention (e.g. agent of harm), and how that is (or is not) related to the outcome or interest (e.g. the disease under investigation).

An example of this type of study investigating vitamin E and Alzheimer’s disease would involve recruiting patients with AD and a set of matched individuals without AD. Both groups (or their caregivers) would be questioned about the individuals’ intake of vitamin E in food and supplements. They would use statistics to determine if cases had more or less vitamin E intake than the controls did, over their lives. These studies are faster than prospective studies, but they are reliant on even a longer memory than prospective studies. Could you figure out how much vitamin E your grandparents ate over their lifespan?

A significant characteristic of observational studies is that while associations (correlations) can be made between exposures and disease development, cause-and-effect (causation) cannot be determined.

Experimental studies

Also called interventional studies, these are designed to test whether a treatment or lifestyle change can alter the onset or course of a disease or condition. Subjects are recruited to take part in the study. Those receiving the treatment are called experimental subjects; those who do not receive the treatment are called controls. Except for the treatment, the conditions that the two groups experience should be the same. Examples of this include things like other foods eaten, amount of exercise, types of daily routines, age, sex, and so forth. Because the only difference between the groups is the treatment, researchers can conclude that differences in outcome between the two groups is due to the treatment. In other words, experiments allow conclusions about cause and effect (causation) to be drawn.

Generally, subjects in the study are randomly assigned to either the experimental or control group. This randomization means the experimenter and the subjects do not choose who gets the treatment, which prevents bias (such as the older subjects being more likely to get the treatment). If it is possible to hide knowledge of whether a person is getting the treatment, a study is said to be blinded. For example, if the study involves taking a new medication in a pill, the experimental group could receive a medicine-containing pill and the controls would receive a pill without medication, known as a placebo. If neither the subjects nor the researchers know who is in which group, the study is called a double-blind study. Obviously, studies cannot be blinded if the treatment is something that cannot be hidden, such as running two miles a day on a treadmill!

The gold standard for human studies is a randomized, double-blind, placebo-controlled experimental study. These may be called clinical trials, especially when health conditions are studied.

Animal studies and in vitro studies

These studies can be useful in answering preliminary questions about safety and identifying how a treatment works without endangering human lives. Results can also lead to hypotheses for clinical testing on humans.

Nutritional Assessment

Nutritional assessment is the interpretation of data to determine whether a person or groups of people are well nourished or malnourished (either over-nourished or under-nourished). Nutritional assessment can be done using the ABCD methods. These refer to the following:

• Anthropometry
• Biochemical methods
• Clinical methods
• Dietary methods

Anthropometric methods of assessing nutritional status

The word anthropometry comes from two words: Anthropo- means ‘human’ and –metry means ‘measurement’. To assess growth, several different measurements including length, height, weight, head circumference, mid-arm circumference, head/chest ratio, and hip/waist ratio can be used. Height and weight measurements are essential to evaluate physical growth in children. The importance of proper measurements is demonstrated by the use of the detailed  Anthropometry Procedures Manual (revised May 2021) in the National Health and Nutrition Examination Survey.

Figure 3.4 shows an example of an anthropometric measurement: body height. A child is standing next to a wall with one person making sure their knees are straight, shins are against the wall, and shoulders are level. The back of the head, shoulder blades, buttocks, shins and heels should be touching the wall. With a hand on the chin, a second person places a board on the head and measures the distance between the spot where the board touches the wall and the floor.

 

Biochemical methods of assessing nutritional status

Biochemical (laboratory) methods include measuring a nutrient or its metabolite in the blood, feces, urine or other tissues that have a relationship with the nutrient. An example of this method is measuring glucose levels in blood. This method is useful for determining if an individual has diabetes.

Clinical methods of assessing nutritional status

Clinical signs and symptoms may suggest nutrient deficiencies. Valuable information may be obtained by experienced clinicians examining skin, eyes, ears, mouth, hair, nails, and gums. Deficiencies or toxicities of nutrients may be evident by changes in the appearance of these and other organs. Asking patients about changes they may have noticed is also important.

Dietary methods of assessing nutritional status

Dietary methods of assessment include looking at past or current intakes of nutrients from food by individuals or a group to determine their nutritional status. There are several methods used to do this:

24 hour recall

A trained professional asks the subject to recall all food and drink consumed in the previous 24 hours. This is a quick and easy method. However, it is dependent upon the subject’s short-term memory and may not be very accurate.

Food frequency questionnaire

The subject is given a list of foods and asked to indicate intake per day, per week, and per month. This method is inexpensive and easy to administer. It is more accurate than the 24-hour recall.

Food diary

Food intake is recorded by the subject at the time of eating. This method is reliable but difficult to maintain. Also known as a food journal or food record.

Observed food consumption

This method requires food to be weighed and exactly calculated. It is very accurate but rarely used because it is time-consuming and expensive.

Evolving Science and Bias

Science is always moving forward, albeit sometimes slowly. One study is not enough to make a guideline or a recommendation or cure a disease. Science is a stepwise process that builds on past evidence and finally culminates into a well-accepted conclusion. Unfortunately, not all scientific conclusions are developed in the interest of human health, and some can be biased. Therefore, it is important to know where a scientific study was conducted and who provided the funding, as this can have an impact on the scientific conclusions being made. For example, the fact that a tobacco company paid for an air quality study likely diminishes the study’s scientific value. Similarly, a study on the nutritional benefits of red meat performed at a laboratory funded by a national beef producers’ association probably suffers from bias.

Nutrigenomics

A new field of study in nutritional science, called nutrigenomics, aims to personalize nutritional information for people based on their genes. Genes, sections of DNA inherited from parents, contain information to make the body’s components. DNA sequences code for RNA and proteins and are responsible for the various traits we possess. Turning genes on and off changes how the body functions. The interaction of genes and the environment, including food choices, is an evolving scientific field. One goal is to find how nutrients impact good health, depending on different DNA sequences in different people. Individualized recommendations may become possible.

Nutrition and the Media

A motivational speaker once said, “A smart person believes half of what they read. An intelligent person knows which half to believe.” In this age of information, where instant Internet access is just a click away, it is easy to be misled if you do not know where to go for reliable nutrition information.

Using Eyes of Discernment

“New study shows that margarine contributes to arterial plaque.”

“Asian study reveals that 2 cups of coffee per day can have detrimental effects on the nervous system.”

How do you react when you read headlines of this nature? Do you avoid margarine and coffee? When reading nutrition-related claims, articles, websites, or advertisements, always remember that one study may not provide a definitive answer. Readers looking for answers to complex nutritional questions can be misled. Listed below are ways that you can develop discerning eyes when reading nutritional news.

The scientific study under discussion should be published in a peer reviewed journal, such as the Journal of Nutrition. Question studies that come from less trustworthy sources (such as non peer-reviewed journals or websites) or that are not formally published.

The report should disclose the methods used by the researcher(s). Did the study last for three or thirty weeks? Were there ten or one hundred participants? What did the participants do? Did the researchers observe the results themselves or did they rely on self-reports from program participants?

Who were the subjects of this study? Humans or animals? If human, are any traits/characteristics noted? Depending on the group of people studied (elderly? children? pregnant women?), the results may be more or less relevant to you.

Credible reports often disseminate new findings in the context of previous research. A single study on its own gives you very limited information, but if a body of literature supports a finding, it adds to credibility.

Reviews or meta-analyses deliver a broad perspective and may be more inclusive than individual research reports.

When reading such news, ask yourself, “Is this making sense?” If the report states that coffee affects the nervous system, is the amount that a person would have to drink realistic? Remember, if a headline professes a new remedy for a nutrition-related topic, it may well be a research-supported piece of news, but it may be a sensational story designed to catch your attention. Track down the original journal article to see if it really supports the conclusions being drawn in the news report.

When reading websites, one way to evaluate the information being presented is to use a set of criteria to help decide if the website is reliable. One set, presented by the Oklahoma Community College library^[8], is described below. It is easy to remember by the initials ABCD, which stand for authority, bias, currency, and documentation.

• Authority: Who is the author? What are the author’s credentials? Does the author have expertise in the area? Is the author associated with a reputable organization?
• Bias: Is the information balanced? Is it more opinion than fact? Does it present facts, or is it designed to sway opinion? Is a product, service, or idea being sold?
• Currency: When was the page last updated? In scientific fields which change quickly, articles over five years old may be out of date. Are any links dead? Is the information consistent with your knowledge in the subject?
• Documentation: Is information documented with references? Are the facts given supported with evidence? If statistics are provided, what is the source? Is I possible to find the original sources? Is the page free of spelling mistakes or other obvious mistakes?

You can read more about the ABCD criteria (https://libguides.occc.edu/ld.php?content_id=12162742) or watched a video about the ABCD criteria (https://www.youtube.com/watch/g6M-ViddtUE) to learn more.

Trustworthy Sources

Let’s consider some reputable organizations and websites from which you can usually obtain valid nutrition information.

Organizations Active in Nutrition Policy and Research

Authoritative nutritional news will be based upon solid scientific evidence, supported by multiple studies, and published in peer-reviewed journals. Whatever the source of your nutritional news, remember to apply the criteria outlined above to help ensure the validity of the information presented. Below are some examples of websites which can be considered credible sources for nutritional news.

US Department of Agriculture Food and Nutrition Information Center (FNIC). The FNIC site (https://www.nal.usda.gov/programs/fnic) has more than 2,500 links to information about diet, nutrition, diet and disease, weight and obesity, food-safety and food-labeling, packaging, dietary supplements and consumer questions. Using this interactive site, you can find tips and resources on how to eat a healthy diet, nutritional information, and a food planner.

The Academy of Nutrition and Dietetics (AND). The AND promotes scientific, evidenced-based, research-supported food and nutrition related information on its website, (https://www.eatright.org/). It is focused on informing the public about recent scientific discoveries and studies, weight-loss concerns, food safety topics, nutrition issues, and disease prevention.

Department of Health and Human Services (HHS). The HHS’s website, (https://www.hhs.gov/), provides credible information about healthful lifestyles and the latest in health news. A variety of online tools such as MyHealthFinder (https://odphp.health.gov/myhealthfinder) are available to assist with food-planning, weight maintenance, physical activity, and dietary goals. You can also find healthful tips for all age groups, tips for preventing disease, and information on daily health issues in general.

Centers for Disease Control and Prevention (CDC). The Centers for Disease Control and Prevention (http://www.cdc.gov) distributes an online newsletter called CDC Vital Signs which provides up-to-date public health information and data regarding food, nutrition, cholesterol, high blood pressure, obesity, teenage drinking, and tobacco usage.

Evaluating Nutrition Research Reports

There are two parts to evaluating reports of discoveries in nutrition research: they type of study and the type of publication. We have already discussed the types of studies that are used in nutrition science; see Table 3.1. above. Different types of publications are discussed next.

Types of Scientific Publications

In the biomedical literature, including nutrition literature, types of publications include:

• A primary source is one in which the authors directly participated in the research or documented their personal experiences. They examined the patients, injected the rats, ran the experiments, or at least supervised those who did. Many, but not all, papers published in biomedical journals are primary sources. An abstract of such a paper should have at least a brief outline of the experimental methods.
• A secondary source summarizes one or more primary or secondary sources, usually to provide an overview of current understanding of the topic, to make recommendations, or to combine results of several studies. Examples include literature reviews or systematic reviews found in medical journals and medical guidelines or position statements published by major health organizations.
• A tertiary source usually summarizes a range of secondary sources. Textbooks, edited scientific books, lay scientific books, and encyclopedias are examples of tertiary sources.
• News or magazine articles or articles in lay-language scientific magazines such as Scientific American are secondary sources, but they are not peer-reviewed and are NOT considered a type of scientific publication. When it comes to reliability, news or magazine reports are the least reliable as they are often written by non-scientists and lack review by scientists in the field.

Primary sources reflect the results of a single study, and these results may conflict with other published primary studies. The reliability of these will vary with the type of experiment, the study design, the sample size, the care taken by the researchers to do the study properly (this can be hard to tell unless you are an expert in the field), and whether the correct statistical analysis is used (determining this takes some real knowledge of statistics). Peer reviewed reports are more reliable, so reading peer-reviewed journals is a good idea.

Secondary sources in biomedical journals, which have been peer-reviewed by other scientists in the field, are usually reliable. In scientific review articles, a scientist in the field summarizes the current state of the field. They may review and aggregate in vitro, animal, and both observational and experimental human studies. Abstracts for scientific review articles will lack experimental details and focus on overall conclusions for a clinical problem.

Another type of secondary study is a meta-analysis. This type of study uses statistics to combine the results of multiple published studies, which increases the sample size. The goal of a meta-analysis is to address the issue of conflicting research reports and attempt to come to a conclusion that is supported by most of the data. An abstract for this type of study will describe the search criteria for finding the studies included as well as a description of the statistical methods. Strong data from meta-analyses and a general scientific consensus can result in publication of treatment or diagnostic guidelines from bodies of experts associated with national or international groups. Examples are such groups relevant to nutrition are the Centers for Disease Control (CDC), National Institute of Health (NIH), United States Department of Agriculture (USDA), Food and Drug Administration (FDA), World Health Organization (WHO), and Academy of Nutrition and Dietetics (AND).

Tertiary sources including textbooks should include information for which there is general scientific consensus; they are generally highly reliable. However, they are often reviewed by educators rather than scientists in the research area, and because of the time it takes to publish a book, may be out of date in rapidly-developing fields.

Using Research Reports for Nutrition Decision-Making

Once a research report is determined to be reliable, the reader will decide whether it addresses the question they are asking. For individuals or organizations making decisions about nutrition and other health-related topics, the weight given to a research report depends on the type of publication as well as the type of study. In general, reports of multiple well-done, randomized, double-blind, placebo-controlled studies with large samples sizes are considered most reliable. Figure 3.6 ranks the types of studies and publications we have discussed, with the type most likely to be used for human health decisions toward the top.

Statistical Analysis of Nutrition Research

Statistics is a branch of mathematics that describes, analyzes, and draws conclusions from data. Because of the complexities in nutrition research, statistical analysis is especially important. To understand the conclusions of nutrition studies, basic understanding of some statistical concepts will help.

The first concept we will discuss is statistical significance, which is the term researchers use to indicate that they are confident that the results of their study are due to what they are studying and not due to random chance. Statistical significance is represented by the p-value. The p-value is a statistical estimate of how likely it is that the difference between the treated and untreated groups would occur randomly; it is expressed as a number between 0 and 1. A small p-value is better and means that the results are more likely to be applicable to larger groups. A p-value of less than 0.05 (commonly written p-value<0.05 or p<0.05) is generally accepted to indicate statistical significance. Researchers accept that there is always a level of uncertainty. Figure 3.7 demonstrates a humorous interpretation of p-values.

Another set of terms commonly used in studies of human subjects includes odds ratio (OR), relative risk (RR), and hazard ratio (HR). These are comparisons of the chance of a particular outcome with or without treatment. An OR, RR, or HR equal to 1 means that the treatment neither increased nor decreased the risk. If OR, RR, or HR is less than 1, the treatment is associated with LESS risk. Values over 1 mean that the risk is increased by the treatment. An OR, RR, or HR of 2 means that treatment leads to twice the risk, while a value of 0.5 means there is half the risk for the treated group compared to the control group.

 

A third concept is that of confidence interval (CI). It is usually expressed as “95% CI” and is a range of values. The range is calculated statistically and indicates that researchers are confident that the answer will fall in this range during 95% of the times that the experiment is repeated. For this reason, a small 95% CI is better and indicates more confidence that the answer is meaningful. Thus:

Large 95% CI = Less confidence in the experimental results

Small 95% CI = More confidence in the experimental results

A confidence interval is normally written in parentheses following an OR, RR, or HR (Figure 3.9) or may be shown by bars on a graph (Figures 3.9, 3.10). Most of the time, the OR, RR, or HR will be found in the middle of the 95% CI, but not always. In general, if the 95% CI includes 1.0, the OR, RR, or HR is not statistically significantly different from 1, which means the exposure or treatment does not have a statistically significant effect on the outcome.

 

Wrapping it up

When interpreting nutritional information, evaluating the source as well as the design of the study is important. Finding the original study and taking a look at its data and the statistical evaluation of the data will help the reader to decide whether to use the information to make nutrition decisions.

References

1. Zimmerman, M.B. Research on Iodine Deficiency and Goiter in the 19th and Early 20th Centuries. Journal of Nutrition. 2008; 138(11), 2060–63. http://jn.nutrition.org/content/138/11/2060.full  Accessed September 17, 2017
2. Carpenter, K.J. David Marine and the Problem of Goiter. Journal of Nutrition. 2005; 135(4), 675–80. http://jn.nutrition.org/content/135/4/675.full?sid=d06fdd35-566f -42a2-a3fd- efbe0736b7ba Accessed September 17, 2017.
3. Myers E. Systems for Evaluating Nutrition Research for Nutrition Care Guidelines: Do They Apply to Population Dietary Guidelines? J Am Diet Assoc. 2003; 12(2), 34–41. http://jandonline.org/article/S0002-8223(03)01378-6/abstract. Accessed September 17, 2017.
4. Briss PA, Zara S, et al. Developing an Evidence-Based Guide to Community Preventive Services—Methods. Am J Prev Med. 2000; 18(1S), 35–43. https://www.ncbi.nlm.nih.gov/pubmed/10806978. Accessed September 17, 2017.
5. US Department of Health and Human Services. Dietary Reference Intakes (DRIs). https://health.gov/our-work/nutrition-physical-activity/dietary-guidelines/dietary-reference-intakes. Updated: January 18, 2023. Accessed August 16, 2024.
6. National Academies of Sciences, Engineering, and Medicine. 2017. Guiding Principles for Developing Dietary Reference Intakes Based on Chronic Disease. Washington, DC: The National Academies Press. https://nap.nationalacademies.org/catalog/24828/guiding-principles-for-developing-dietary-reference-intakes-based-on-chronic-disease. Accessed August 16, 2024.
7. Food and Nutrition – Nutrition – Dietary Reference Intakes. National Academies of Sciences, Engineering, and Medicine. https://nap.nationalacademies.org/topic/380/food-and-nutrition/nutrition-dietary-reference-intakes Accessed August 16, 2024.
8. Occclibrary. (2012, January 9). Evaluating Websites. YouTube. https://www.youtube.com/watch?v=g6M-ViddtUE.

Attributions

Adapted by by Pattie S. Green, Ph.D., and Jonathan E. Pottle, Ph.D., Tacoma Community College, from the following sources:

• Human Nutrition by University of Hawai‘i at Mānoa Food Science and Human Nutrition Program, which is licensed under a Creative Commons Attribution 4.0 International License.
  • Research and the Scientific Method
  • Types of Scientific Studies
• Kansas State University Human Nutrition (FNDH 400) Flexbook, “Nutrition Research Statistics,” by Lindshield, B. L. (2018). by NPP eBooks. 19. CC BY-NC-SA 4.0 license.