11 1.7 Interpreting Research
A systematic literature review does what the name implies, it systematically reviews the literature related to a certain research question. For example, the research question might be, “Does chocolate decrease blood pressure?” There is a method for performing the review established ahead of time that details answers to questions such as:
How will journal articles be identified?
Using what databases?
What search terms will be used?
The end product is a conclusion based on the evidence in the identified journal articles. A person in the following video compares it to reading Consumer Reviews or a consumer report about something that you are going to buy. The Cochrane Collaboration performs many systematic reviews; the first link is to a video about the Cochrane Collaboration, the second is a link to the site itself.
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Because they synthesize the findings from multiple trials, systematic literature reviews are considered the highest level of nutrition research evidence and are therefore shown at the top of the strength of nutrition research pyramid below. In vitro studies are shown at the bottom of the triangle because they are the weakest form of evidence overall. It should be pointed out that most systematic literature reviews only consider epidemiological studies and clinical trials and do not include animal studies or in vitro evidence. While these studies are of less strength, they should still be considered.
There are a couple of other factors to consider relating to the different forms of research. First, epidemiological studies cannot show causality (i.e. smoking causes lung cancer), but instead identify relationships or associations (i.e. smoking is associated with lung cancer occurrence). Clinical trials/human studies are the best form of primary research because their findings should be directly translatable to patients. So why use other forms of research? The description below should help explain why the other forms of research are also important.
In general, a certain sequence of studies in nutrition research is often followed as shown in the figure below.
Epidemiological studies find relationships between food/food components and a specific health outcome. This relationship is then investigated by in vitro studies and then, some of the most promising move to animal studies. Then the most promising and safe food/food components are moved into clinical trials/human studies. If it is an individual compound, there will be smaller trials designed to see if the compound is safe before it is moved into larger clinical trials to determine whether the food/food component results in beneficial health outcomes. The overall effect of this process is to select the most promising and safe food/food components for the clinical trials/human studies. This allows time and money to be used more efficiently, because while clinical trials/human studies are the best form of research, they are also normally the most e