1.5.2. Nutritional Science

Research and the Scientific Method

Photo by Jonathon Simcoe on unsplash.com / CC0

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. This organized process of inquiry used in science is called the scientific method.

Figure Scientific Method Steps

Source: Research and Scientific Methods

The Scientific Method in Action

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 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.
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 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. [2]
Results. This study was conducted on over four-thousand school children, and found that iodized salt prevented goiter.

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


Everyday 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? Where is your money invested? What college do you attend?

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.

Types of Scientific Studies

There are various types of scientific studies on humans that can be used to provide supporting evidence for a particular hypothesis. These include epidemiological studies, interventional clinical trials, and randomized clinical trials. Valuable nutrition knowledge also is obtained from animal studies and cellular and molecular biology research.

Table Types of Scientific Studies

Type Description Example Notes
Epidemiological studies Observational study of populations around the world and the impact of nutrition on health. Diets with a high consumption of saturated fat are associated with an increased risk of heart attacks. Does not determine cause-and-effect relationships.
Intervention clinical trials Scientific investigations where a variable is changed between groups. Testing the effect of different diets on blood pressure. One group consumes an American diet, group 2 eats a diet rich in fruits and vegetables, and group 3 eats a combination of groups 1 and 2. If done correctly, it does determine cause-and-effect relationships.
Randomized clinical trials (RCTs)  Participants are assigned by chance to separate groups that compare different treatments. Neither the researchers nor the participants can choose which group a participant is assigned. Testing the effect of calcium supplements on women with osteoporosis. Participants are given a pill daily of a placebo or calcium supplement. Neither the participant nor the researcher know what group the participant is in. Considered the “gold” standard for scientific studies.
Studies of animal and cellular biology Studies are conducted on animals or on cells. Testing the effects of a new blood pressure drug on guinea pigs or on the lipid membrane of a cell. Less expensive than human trials. Study is not on whole humans so it may be not applicable.

Note: There are various type of scientific studies that can be conducted. These studies range in strength with RCTs being the gold standard.

Nutrition Assessment

Nutritional assessment is the interpretation of anthropometric, biochemical (laboratory), clinical and dietary data to determine whether a person or groups of people are well nourished or malnourished (overnourished or undernourished).

Nutritional assessment can be done using the ABCD methods. These refer to the following:

  • A: Anthropometry
  • B: Biochemical methods
  • C: Clinical methods
  • D: Dietary methods

Anthropometry Methods of Assessing Nutritional Status

The word anthropometry comes from two words: Anthropo means ‘human’ and metry means ‘measurement’. The different measurements taken to assess growth and body composition are presented below.

To assess growth, several different measurements including length, height, weight, head circumference, mid-arm circumference, skin-fold thickness, head/chest ratio, and hip/waist ratio can be used. Height and weight measurements are essential in children to evaluate physical growth. As an additional resource, the NHANES Anthropometry Procedures Manual (revised January 2004) can be viewed here https://www.cdc.gov/nchs/data/nhanes/nhanes_03_04/BM.pdf

Figure Measuring Height

Source: UNICEF, 1986, How to weigh and measure children: assessing the nutrition status of young children. CC BY 4.0 license

Biochemical Methods of Assessing Nutritional Status

Biochemical or laboratory methods of assessment 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 would be to take blood samples to measure levels of glucose in the body. This method is useful for determining if an individual has diabetes.

Figure Measuring Blood Glucose Levels

A woman testing her blood sugar levels
Source: image by TesaPhotography / CC0.

Clinical Methods of Assessing Nutritional Status

In addition to the anthropometric assessments, you can also assess clinical signs and symptoms that might indicate potential specific nutrient deficiency. Special attention are given to organs such as skin, eyes, tongue, ears, mouth, hair, nails, and gums. Clinical methods of assessing nutritional status involve checking signs of deficiency at specific places on the body or asking the patient whether they have any symptoms that might suggest nutrient deficiency.

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

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, an air quality study paid for by a tobacco company diminishes its value in the minds of readers as well as a red meat study performed at a laboratory funded by a national beef association.

Nutritional Science Evolution

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 of 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.

Using Science and Technology To Change the Future

As science evolves, so does technology. Both can be used to create a healthy diet, optimize health, and prevent disease. Picture yourself not too far into the future: you are wearing a small “dietary watch” that painlessly samples your blood, and downloads the information to your cell phone, which has an app that evaluates the nutrient profile of your blood and then recommends a snack or dinner menu to assure you maintain adequate nutrient levels. What else is not far off? How about another app that provides a shopping list that adheres to all dietary guidelines and is emailed to the central server at your local grocer, who then delivers the food to your home? The food is then stored in your smart fridge which documents your daily diet at home and delivers your weekly dietary assessment to your home computer. At your computer, you can compare your diet with other diets aimed at weight loss, optimal strength training, reduction in risk for specific diseases or any other health goals you may have. You also may delve into the field of nutritional genetics and download your gene expression profiles to a database that analyzes your genes against millions of others.

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 two cups of coffee per day can have detrimental effects on the nervous system.”

How do you react when you read news of this nature? Do you boycott margarine and coffee? When reading nutrition-related claims, articles, websites, or advertisements, always remember that one study does not substantiate a fact. One study neither proves nor disproves anything. Readers who may be looking for complex answers to nutritional dilemmas can quickly misconstrue such statements and be led down a path of misinformation. Listed below are ways that you can develop discerning eyes when reading nutritional news:

  1. 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.
  2. 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 actually do? Did the researcher(s) observe the results themselves or did they rely on self reports from program participants?
  3. Who were the subjects of this study? Humans or animals? If human, are any traits/characteristics noted? You may realize you have more in common with certain program participants and can use that as a basis to gauge if the study applies to you.
  4. 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.
  5. Peer-reviewed articles deliver a broad perspective and are inclusive of findings of many studies on the exact same subject.
  6. When reading such news, ask yourself, “Is this making sense?” Even if coffee does adversely affect the nervous system, do you drink enough of it to see any negative effects? Remember, if a headline professes a new remedy for a nutrition-related topic, it may well be a research-supported piece of news, but more often than not, it is a sensational story designed to catch the attention of an unsuspecting consumer. Track down the original journal article to see if it really supports the conclusions being drawn in the news report.

When reading information on websites, remember the following criteria for discerning if the site is valid:

  1. Who sponsors the website?
  2. Are names and credentials disclosed?
  3. Is an editorial board identified?
  4. Does the site contain links to other credible informational websites?
  5. Even better, does it reference peer-reviewed journal articles? If so, do those journal articles actually back up the claims being made on the website?
  6. How often is the website updated?
  7. Are you being sold something at this website?
  8. Does the website charge a fee?

For more information, visit http://www.csuchico.edu/lins/handouts/eval_websites.pdf

Trustworthy Sources

Now 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:

  • Health Canada provides information on an extensive number of subjects relating to the Health of Canadian citizen. Topics include but are not limited to; healthy living, food and nutrition, environmental and workplace health and drugs and health products. Visit their website to explore their content. 
  • Canadian Society for Exercise Physiology (CSEP) website provides physical activity guidelines and recommendations for Canadians of all ages. 
  • US Department of Agriculture Food and Nutrition Information Center. The USDA site http://fnic.nal.usda.gov 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, http://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 website, HealthFinder.gov, provides credible information about healthful lifestyles and the latest in health news. A variety of online tools 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.

  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.


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Fundamentals of Health and Physical Activity by Kerri Z. Delaney and Leslie Barker is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.