Nutrition Research and 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 developed in the 17th century is used in the sciences including nutritional science, and is called the scientific method.

One example of how the scientific method has been used in nutritional sciences is in the identification of the mineral iodine and it’s role in the thyroid gland. In the early 1800s the development of an enlargement of the neck, known as a goiter, was common in the population, especially in those living far from the sea. It was thought to be caused by poor hygiene. Because of the use of the scientific method, we now know that a goiter develops when iodine in the diet is deficient. Below is a description of how this was determined.

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 using the steps of the scientific method: observation, hypothesis, experimental test, interpretation of results.^[1]Repeat these steps to gather more evidence until you have enough evidence to reach a conclusion.

Steps of the Scientific Method used to identify Iodine

Observation. Eating seaweed is a cure for goiter, an enlargement of the thyroid gland in the neck.

Hypothesis. In 1813, Swiss physician Jean-Francois Coindet hypothesized that the seaweed contains 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 proposed that the low iodine content in food and water of certain areas far away from the ocean were 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.

Results. The program was effective and 80% of children with goiter were cured.

Hypothesis. In 1918, Swiss doctor Bayard proposed iodizing salt as a good way to treat areas where much of the population suffered from goiter.

Experimental test. Iodized salt was transported by mules to a small village at the base of the Matterhorn where more than 75% of school children had goiter. 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.^[2]

Results. This study conducted on over 4,000 school children found that iodized salt prevents 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% 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.

This is just one example of how the scientific method was used to determine how to treat a specific health condition. There have been millions of studies using this method, and you are benefitting from the results of these studies when you take a medication for a specific disease or condition, or when you modify a behavior to achieve a desired result.

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 part of the overall evidence-based approach to designing nutritional guidelines. An evidence-based approach to nutrition includes:^[3]

• Defining the problem or uncertainty (e.g., the rate of colon cancer is higher in people who eat red meat)
• Formulating it as a question (e.g., does eating red meat contribute to colon cancer?)
• Setting criteria for quality evidence
• Evaluating the body of evidence
• Summarizing the body of evidence and making decisions
• Specifying the strength of the supporting evidence required to make decisions
• Disseminating the findings

The Food and Nutrition Board of the National Academy of Medicine (NAM) [formerly known as the Institute of Medicine (IOM)], a non-profit, non-governmental organization, constructs its nutrient recommendations (i.e., Dietary Reference Intakes, or DRI) using an evidence-based approach to nutrition. The entire procedure for setting the DRI is documented and made available to the public. The same approach is used by the US Department of Agriculture (USDA) and US Department of Health and Human Services (HHS). 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.

Types of Scientific Studies

There are many types of scientific studies that can be used to test a particular hypothesis including epidemiological studies, interventional clinical trials, and randomized clinical interventional trials.

Epidemiological studies observe what is actually happening in a population in relation to health over time. The goal is to find factors associated with an increased or decreased risk for a health event, though these sometimes remain elusive. Often these types of studies can help refine a hypothesis. They can be used to predict future health needs, but cannot directly determine if one variable causes another.

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. A randomized clinical interventional trial is a study in which participants are assigned by chance to separate groups that compare different treatments. Neither the researchers nor the participants can choose or know which group a participant is assigned to. That’s called a double blind study. In these types of studies, the control group usually receives a placebo instead of the actual intervention. These are powerful tools to provide supporting evidence for a particular relationship and are considered the “gold standard” of scientific studies.

High quality clinical interventional trial studies are:

• 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 groups, 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.
• “double-blinded” studies in which neither the researchers nor the participants know into which group they have been assigned. This is done to reduce bias on the part of the researchers.
• those studies that include a sufficient number of participants (signified by “n”). Generally the higher the “n” the more robust and significant is the study.

The limitations of clinical intervention studies 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.)

Because of the types of study 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.

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 are less expensive than human studies and they require less time to conduct. 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. The main disadvantage of these types of studies is that researchers are not working with whole humans and thus the results may not be as applicable. Nevertheless, well-conducted animal and cell studies that can be repeated by multiple researchers and obtain the same conclusion are definitely helpful in building the evidence to support a scientific hypothesis.

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 step-by-step, gradual 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 it is important to know where a scientific study was conducted and who provided the funding for the study. This can help you identify bias. Bias means that a researcher or group prefers one outcome over another, so they do not give all possible outcomes an equal chance. If you read an air quality study paid for by a tobacco company that found that smoking did not reduce indoor air quality, you would be skeptical of that result. You should also be skeptical of one on the benefits of red meat performed at a laboratory funded by a national beef association, or the benefits of a dietary supplement paid for by a supplement manufacturing corporation.

Science can also be contentious even among experts that do not have any conflicting financial interests. Contentious science is actually a good thing as it forces researchers to be of high integrity, well-educated, well-trained, and dedicated. It also instigates public health policy makers to seek out multiple sources of evidence in order to support a new policy. 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.

references

Chapter 1, section 1.4 from Consumer Nutrition by Megan Grimsley and Susan Kazen published in 2021 under a CC BY-NC-SA license.