Nutrition Research: Design Process & Types of Studies

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

In this lesson, we learn about different kinds of nutritional research used to develop nutritional advice. We will also examine the limitations of each type of research.

Nutritional Advice

''Cut carbs.''

''Eat more fiber.''

''Avoid fat.''

''Eat more meat.''

''Go vegetarian.''

There seems to be so much nutritional advice out there, and a lot of it tends to be contradictory. It can lead us to wonder, ''where do they even come up with this stuff?!''

While there may not be a rhyme or reason to how non-scientists or entrepreneurs interpret the results, professional nutritionists develop their recommendations based on nutritional research. Learning how to evaluate nutritional research and its different design processes can help someone determine for themselves whether or not the nutritional advice is sound.

The US government developed nutritional advice based on nutritional research
My plate

Good nutritional research follows the scientific method. The scientific method follows the following steps:

  1. Ask a question
  2. Formulate a hypothesis
  3. Design and perform an experiment
  4. Analyze the experiment results
  5. Draw up conclusions and share results

Experimental Design

Coming up with a good question and developing the hypothesis are important steps. These steps need to be based on prior research and gaps in current knowledge. Once these steps have been developed, an experiment needs to be designed.

In nutritional research, primary or secondary research can be conducted. Primary research occurs when scientists gather their own data to analyze. Secondary research occurs when scientists analyze the results from other research, and make conclusions based on the results from other researchers. Secondary research can be really important in order to summarize data and help draw conclusions when results from different studies seem to be contradictory. Typically, however, researchers want to focus on primary research.

There are four main types of primary research for nutrition:

  • Animal or laboratory
  • Case-control
  • Cohort
  • Randomized

Types of research

Animal and laboratory studies are when the effects of a nutrient or food are examined in animals or cells in a test tube. These types of studies are frequently done in nutrition because it is difficult to ethically perform randomized studies on humans. For example, nutritionists cannot set up a study and tell one group of people to not eat protein because if the study went on for too long, those participants would die or suffer serious health consequences. So, the next best thing is to do the study on animals and hope the results translate in a similar way to humans.

Rats fed copper and rats not fed copper helped lead to a better understanding of copper deficiencies
Rats with and without copper

Case-control studies take a group of people who have a specific condition or outcome, such as diabetes or successful lost weight. The studies then compare that group to a group who doesn't have that condition or outcome. Researchers ask questions about the behavior of the group members. For example, nutritionists may ask how many servings of fruits and vegetables did members from each group eat a day. This type of study is helpful because we are actually using people. However, a shortcoming is that we are relying on people to remember what they have done in the past and to accurately report it.

Cohort studies gather a large group of people and follow them for an extended period of time. This can even be for 20 or more years! Throughout the course of the study, data will be collected on the participants. For example, participants may need to keep a food journal detailing what they have eaten each day. At the end of the study (and often during certain check points throughout the study) each participant will be tested for a variety of health conditions. The foods eaten can then be compared to the health conditions that participants have. This type of study is better than case-control because researchers are not relying on participants to recall past events. These studies are limited, however, because there is still no randomization.

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