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1.3: The Broad Role of Nutritional Science

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    20912
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    Learning Objectives
    • Describe the scientific method.
    • Identify various types of scientific studies.

    The Scientific Method

    Similar to the method by which a police detective finally charges a criminal with a crime, nutritional scientists discover the health effects of food and its nutrients by first making an observation. Once observations are made, they come up with a hypothesis, test their hypothesis, and then interpret the results. After this, they gather additional evidence from multiple sources and finally come up with a conclusion on whether the food suspect fits the claim. This organized process of inquiry used in forensic science, nutritional science, and every other science is called the scientific method.

    The scientific method includes making observations, forming a hypothesis, conducting an experiment, and deciding if data supports the hypothesis.Figure \(\PageIndex{1}\): Steps of the scientific method (CNX OpenStax / CC BY creativecommons.org/licenses/by/4.0)

    When confronted with a claim, scientists must consider the evidence that supports or does not support the claim. A standardized method, called the scientific method, is used to look at the evidence. The scientific method includes the following steps:

    1. The researcher makes an observation and description of an event.
      • Observations of an event lead the researcher to ask a question.
      • Example: You've noticed that the people you know who eat apples don't go to the doctor as often as other people you know who don't eat apples, leading you to the question "Does an apple a day really keep the doctor away?" 
    2. The researcher proposes a hypothesis (educated guess) to explain why the event occurs. 
      • A hypothesis is also referred to as a research question.
      • A hypothesis is written in a way so that it can be evaluated as either true or false.
      • A hypothesis must be testable, unbiased and repeatable.
      • Example: Your hypothesis could be "People who eat an average of 1 or more apples per day have fewer visits to the doctor than people who eat less than 1 apple per day."
    3. The researcher develops an experiment that will test the hypothesis.
      • An experiment is a scientific study that tests the hypothesis.
      • Key elements of a well-designed experiment include:
        • Sample Size - enough people must be studied to ensure that the results obtained are not due to chance alone.
        • Control Group
          • A group of people who are as much like the group of people in the experiment as possible except for the variable being tested.
          • Using a control group helps the researcher judge whether the treatment worked or not.
          • Example: In the apple study you would want a group of people who eat apples regularly (experimental or treatment group) and a similar group of people who are like the treatment group in every way except that they don't eat apples (control group).
          • Scientists compare the 2 groups by plotting variables on a graph.
            • Independent variable
              • controlled by the researcher
              • plotted on the horizontal axis (x axis)
              • example: the number of apples eaten per day
            • Dependent variable
              • not controlled by the researcher
              • observed or measured by the researcher
              • plotted on the vertical axis (y axis)
              • also called the outcome variable
              • example: the number of doctor visits
        • Researcher should attempt to control for other variables that may influence the results
          • Example: Since age may be one reason why people go to the doctor more often, we would want to make sure that we had the same ages of people in each group.
    4. The researcher collects and analyzes data that will either support or reject the hypothesis.
      • Data should be collected in the most reliable and consistent way possible.
      • Example: More reliable information would be collected from the doctor's office charts than simply asking participants to remember how many times they went to the doctor over the past year.
      • If the data do not support the hypothesis, then the hypothesis is either rejected or an alternate hypothesis may be proposed and tested.
      • If the data support the original hypothesis, then a conclusion is drawn. More experiments are typically conducted to further test and confirm support for the hypothesis.
      • If multiple experiments consistently support the hypothesis, then the hypothesis beomes more widely accepted in the scientific community.

    Below is another illustration of the scientific method at work—in this case to prove that iodine is a nutrient.1,2

    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. The following scientific record is some of what took place in order to conclude that iodine is a nutrient.

    • 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 he could use just iodine instead of seaweed to treat his patients.
    • Experimental test. Coindet administered iodine tincture orally to his patients with goiter.
    • Interpret results. Coindet’s iodine treatment was successful.
    • Gathering more evidence. Many other physicians contributed to the research on iodine deficiency and goiter.
    • Hypothesis. French chemist Chatin hypothesized that the low iodine content in food and water of certain areas far away from the ocean were the primary cause of goiter (as opposed to a former 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.
    • Results. The program was effective and 80 percent of goitrous children were cured.
    • Hypothesis. In 1918, Swiss doctor Bayard proposed iodizing salt as a good way to treat areas endemic with goiter.
    • 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. It was given to families to use for six months.
    • Results. The iodized salt was beneficial in treating goiter in this remote population.
    • Experimental test. Physician David Marine conducted the first experiment of treating goiter with iodized salt in America in Akron, Ohio.
    • Results. This study conducted on over four-thousand school children found that iodized salt prevented goiter.
    • Conclusions. Seven other studies similar to Marine’s were conducted in Italy and Switzerland that also demonstrated the effectiveness of iodized salt in treating goiter. In 1924, US public health officials initiated the program of iodizing salt and started eliminating the scourge of goiterism. Today more than 70 percent of American households use iodized salt and many other countries have followed the same public health strategy to reduce the health consequences of iodine deficiency.

    Evidence-Based Approach to Nutrition

    It took more than 100 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 also part of the overall evidence-based approach to designing nutritional guidelines. The Food and Nutrition Board of the Institute of Medicine, a nonprofit, nongovernmental organization, constructs its nutrient recommendations (i.e., Dietary Reference Intakes, or DRIs) using an evidence-based approach to nutrition. The entire procedure for setting the DRIs is documented and made available to the public. The same approach is used by the USDA and HHS, which are departments of the US federal government. The USDA and HHS websites are great tools for discovering ways to optimize health; however, it is important to gather nutrition information from multiple resources as there are often differences in opinion among various scientists and public health organizations. While the latest Dietary Guidelines have been well-received by some, there are nongovernmental public health organizations that are convinced that some pieces of the guidelines may be influenced by lobbying groups and/or the food industry. For example, the Harvard School of Public Health (HSPH) feels the government falls short by being "too lax on refined grains." The guidelines recommend getting at least half of grains from whole grains—according to the HSPH this still leaves too much consumption of refined grains.

    Types of Scientific Studies

    There are many types of scientific studies that can be used to provide supporting evidence for a particular hypothesis. The various types of studies include epidemiological studies, clinical trials, and laboratory studies.

    Epidemiological Studies

    Epidemiological studies are observational studies that look for health patterns and are often used to inform public health. The CDC defines epidemiological studies as scientific investigations that define frequency, distribution, and patterns of health events in a population. Thus, these studies describe the occurrence and patterns of health events over time. The goal of an epidemiological study is to find factors associated with an increased risk for a health event, though these sometimes remain elusive. An example of an epidemiological study is the Framingham Heart Study, a project of the National Heart, Lung and Blood Institute and Boston University that has been ongoing since 1948. This study first examined the physical health and lifestyles of 5,209 men and women from the city of Framingham, Massachusetts and has now incorporated data from the children and grandchildren of the original participants.3 One of the seminal findings of this ambitious study was that higher cholesterol levels in the blood are a risk factor for heart disease.

    Epidemiological studies are used to examine and evaluate public health. Some advantages of epidemiological studies are that they can lead to the discovery of disease patterns and risk factors for diseases. In addition, they can be used to predict future healthcare needs and provide information for the design of disease prevention strategies for entire populations. Some shortcomings of epidemiological studies are that investigators cannot control environments and lifestyles, a specific group of people studied may not be an accurate depiction of an entire population, and these types of scientific studies cannot directly determine if one variable causes another. Scientists regard epidemiological studies as a starting place for ideas about which lifestyle choices MAY contribute to a disease. They can show a CORRELATION between two things happening but NOT whether one factor CAUSED the other. Epidemiological studies may give us ideas but those ideas need clinical trials to figure out what the patterns mean.

    Clinical Trials

    Interventional clinical trial studies are scientific investigations in which a variable is changed between groups of people. When well done, this type of study allows one to determine causal relationships. An example of an interventional clinical trial is a study in Spain that is investigating the effect of a the Mediterranean diet on prevention of cardiovascular diseases. There are many studies that are part of the Prevention with Mediterranean Diet (PREDIMED) trials. In one study4, 7,447 participants were randomly assigned to three different groups; one group followed a Mediterranean diet supplemented with extra-virgin olive oil, the second group followed a Mediterranean diet supplemented with mixed nuts, and the third group was given advice to reduce dietary fat. The two groups following the Mediterranean diet are considered intervention groups; the third group that was simply given advice to follow a reduced-fat diet is considered a control group. All three groups were followed for nearly 5 years to determine effects of the various diets on major cardiovascular events (heart attack, stroke, or death from cardiovascular causes). Results of the study showed that the groups following the Mediterranean diet (supplemented with either extra-virgin olive oil or nuts) had a lower incidence of major cardiovascular events than participants who were assigned to a reduced-fat diet.

    The attributes of high-quality clinical interventional trial studies are:

    • those studies that include a sufficient number of participants;
    • those that include a control group, which does not receive the intervention, to which you can compare the people who receive the intervention being tested;
    • those in which the subjects are randomized into the control group or intervention group, meaning a given subject has an equal chance of ending up in either the control group or the intervention group. This is done to ensure that any possible confounding variables are likely to be evenly distributed between the control and the intervention groups.
      • What are confounding variables? These are factors other than the one being tested that could influence the results of the study. For instance, in the study we just considered, if one group of adults did less physical activity than the other, then it could be the amount of physical activity rather than the diet being tested that caused the differences in major cardiovascular events among the groups.
    • ideally, neither the researchers nor the participants will know who is receiving the treatment - when this occurs, the experiment is known as a double-blind experiment.
      • the blinding process can include a placebo treatment (imitation treatment that has no effect on participants)
      • The "placebo effect" should always be considered. Sometimes, just knowing that they're in a study will cause participants to experience changes that they would attribute to the treatment - regardless of whether they receive the treatment or the placebo.

    Randomized clinical interventional trial studies are powerful tools to provide supporting evidence for a particular relationship and are considered the “gold standard” of scientific studies. However, from their limitations it is clear that epidemiological studies complement interventional clinical trial studies and both are necessary to construct strong foundations of scientific evidence for health promotion and disease prevention.

    The limitations of clinical trials are that they are difficult to carry on for long periods of time, are costly, and require that participants remain compliant with the intervention. Furthermore, it is unethical to study certain interventions. (An example of an unethical intervention would be to advise one group of pregnant mothers to drink alcohol to determine the effects of alcohol intake on pregnancy outcome, because we know that alcohol consumption during pregnancy damages the developing fetus.)

    Laboratory Studies

    Other scientific studies used to provide supporting evidence for a hypothesis include laboratory studies conducted on animals or cells. An advantage of this type of study is that they typically do not cost as much as human studies and they require less time to conduct. These studies can also provide preliminary information to assist in designing human studies. Other advantages are that researchers have more control over the environment and the amount of confounding variables can be significantly reduced. Moreover, animal and cell studies provide a way to study relationships at the molecular level and are also helpful in determining the exact mechanism by which a specific nutrient causes a change in health. Laboratory studies may also be used when research cannot be done with humans.

    The disadvantage of these types of studies are that researchers are not working with whole humans and thus the results may not be relevant or may not always apply directly to humans. In addition, studies involving animals may have ethical implications. Nevertheless, well-conducted animal and cell studies that can be repeated by multiple researchers and obtain the same conclusion are helpful in building the evidence to support a scientific hypothesis. 

    Evolving Science

    Science is always moving forward, albeit sometimes slowly. One study is not enough to make a guideline, recommendation, or cure a disease. Science is a stepwise process that builds on past evidence and finally culminates into a well-accepted conclusion. Agreement involving many experts across multiple scientific disciplines is necessary for recommending dietary changes to improve health and prevent disease. Although a somewhat slow process, it is better for our health to allow the evidence to accumulate before incorporating some change in our diet.

    One of the newest areas in the realm of nutritional science is the scientific discipline of nutritional genetics, also called nutrigenomics. Genes are part of DNA and contain the genetic information that make up all our traits. Genes are codes for proteins and when they are turned “on” or “off,” they change how the body works. While we know that health is defined as more than just the absence of disease, there are currently very few accurate genetic markers of good health. Rather, there are many more genetic markers for disease. However, science is evolving and nutritional genetics aims to identify what nutrients to eat to “turn on” healthy genes and “turn off” genes that cause disease. Eventually this field could progress to the point that a person’s diet can be tailored to their genetics. Thus, your DNA could someday determine your optimal diet!

    Key Takeaways

    • The scientific method is an organized process of inquiry used in nutritional science.
    • The scientific method is part of the overall evidence-based approach to designing nutritional guidelines that are based on facts.
    • There are different types of scientific studies—epidemiological studies, randomized clinical interventional trial studies, and laboratory animal and cell studies—which all provide different, complementary lines of evidence.
    • It takes time to build scientific evidence that culminates as a commonly accepted conclusion.
    • Agreement of experts across multiple scientific disciplines is a necessity for recommending dietary changes to improve health and help to prevent disease.
    • Science is always evolving as more and more information is collected.

    References

    1. Zimmerman MB. Research on iodine deficiency and goiter in the 19th and early 20th centuries. J Nutr. 2008;138(11):2060–63.
    2. Carpenter KJ. David Marine and the problem of goiter. J Nutr. 2005;135(4):675–80.
    3. Framingham Heart Study. History of the Framingham Heart Study. https://framinghamheartstudy.org/fhs-about/history/. Accessed June 1, 2020.
    4. Estruch E, Ros E, Salas-Salvado J, et al; PREDIMED Study Investigators. Primary prevention of cardiovascular disease with a Mediterranean diet supplemented with extra-virgin olive oil or nuts. N Engl J Med. 2018;378:e34.

    1.3: The Broad Role of Nutritional Science is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by LibreTexts.

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