Unit 3 – The Science of Nutrition

3.2 The Scientific Method

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What is the Scientific Method?

Similar to the method by which a police detective investigates a crime, nutritional scientists discover the health effects of food and nutrients by first making an observation and posing a question that they’d like to answer. Then they formulate a hypothesis, test their hypothesis through experiments, and finally interpret the results. After analyzing additional evidence from multiple sources, they may conclude 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.

Figure 3.1 Scientific Method Steps

Diagram showing the scientific method steps: 1-Ask a Question, 2-Do Background Research, 3-Form a Hypothesis, 4-Test Your Hypothesis, 5-Analyze the Data, 6-Determine Your Conclusion
Scientific Method steps


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 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 that iodine could be used instead of seaweed to treat his patients[1].

Figure 3.2. “Large Goiter in Woman” by E. Theodor Kocher

Experimental test. Coindet administered iodine tincture orally to his patients with goiter.

Interpret results. Coindet’s iodine treatment was successful.

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.

Results. The program was effective, and 80 percent of goitrous children were cured.

Hypothesis. In 1918, Swiss doctor Bayard proposed iodizing salt as an excellent way to treat areas endemic to 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.[2]

Results. This study was conducted on over four-thousand schoolchildren, and found that iodized salt prevented goiter.

Conclusions. Seven other studies similar to Marine’s were conducted in Italy and Switzerland, demonstrating 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 goiter. 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.

VIDEO: Peer Review in 3 Minutes” by libncsu, YouTube (May 1, 2014), 3:14 minutes



Review Quesitons

Career Connection

What are some of the ways in which you think like a scientist, and use the scientific method in your everyday life? Any decision-making process uses some aspect of the scientific method. Think about some of the major decisions you have made in your life and the research you conducted that supported your decision. For example, what brand of computer do you own? How do you save money? What are your plans after graduation?

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 (e.g., Does eating seaweed decrease the risk of goiter?)
  • 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 Institute of Medicine, a nonprofit, 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 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. Full text versions of the DRI publications are available in pdf format at https://www.nap.edu/, along with many other free publications.

Learning Activities

Technology Note: The following activity was created by the University of Hawai‘i at Mānoa Food Science and Human Nutrition Program as an  Open Educational Resource (OER) textbook.   Throughout this book, we have included several of their colorful and interactive review activities.

Learning activities may be used across various mobile devices, however, for the best user experience it is strongly recommended that users complete these activities using a desktop or laptop computer and in Google Chrome.


  1. Zimmerman, M.B. (2008). Research on Iodine Deficiency and Goiter in the 19th and Early 20th Centuries. Journal of Nutrition, 138(11), 2060–63. http://jn.nutrition.org/content/138/11/2060.full
  2. Carpenter, K.J. (2005). David Marine and the Problem of Goiter. Journal of Nutrition, 135(4), 675–80. http://jn.nutrition.org/content/135/4/675.full?sid=d06fdd35-566f -42a2-a3fd- efbe0736b7ba
  3. Myers E. (2003). Systems for Evaluating Nutrition Research for Nutrition Care Guidelines: Do They Apply to Population Dietary Guidelines? Journal of the American Dietetic Association, 12(2), 34–41. http://jandonline.org/article/S0002-8223(03)01378-6/abstract
  4. Briss PA, Zara S, et al. (2000). Developing an Evidence-Based Guide to Community Preventive Services—Methods. Am J Prev Med, 18(1S), 35–43. https://www.ncbi.nlm.nih.gov/pubmed/10806978


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Introduction to Nutrition and Wellness Copyright © 2022 by Janet Colson; Sandra Poirier; and Yvonne Dadson is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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