Why does nutrition research matter?
Nutrition research is integral to how we understand the impacts of various foods and/or behaviors on health. In looking for research, one of the best places to start is PubMed, a free U.S. government-run website that allows users to search for health related literature.
PubMed can be a quick way to decipher between a health-related claim and quackery. In other words, if someone claims that “eating 10 bowls of spinach a day prevents sickness,” but there are zero articles to be found on the topic, then it’s likely a dubious claim. With that said, PubMed doesn’t necessarily decipher good research from bad research; in other words, just because it’s on PubMed doesn’t mean it’s substantiated. PubMed is simply a database for ALL research.
How do you decipher good research from bad research?
In an ideal setting, researchers conduct experiments that utilize interventions to answer a question (hypothesis). Let’s say, as an example, the hypothesis is “Does a diet rich in minimally processed foods reduce risk of disease?” To answer the question, participants are randomly placed into different groups. One group receives the intervention (or “treatment,”) for example, a diet low in “processed” foods and the other receives a control (or “placebo”) for example, a diet high in “processed” foods.
These Randomized Controlled Trials (RCTs) are considered the “gold standard” of scientific research. RCTs are usually performed in a controlled setting (such as in a lab) where external influences are limited. Though ideal, RCTs are too expensive and impractical to conduct long-term (plus, we can’t expect study participants to fully follow diet rules when we know that success rates with dieting are insanely low).
In looking for good research, RCTs that are performed on human subjects will be most reliable and relatable. This is important to consider when deciphering nutrition fact from fiction: studies performed on rats do not translate to conclusive evidence for us! If RCTs on the claim in question do not exist, then chances are the claim is not substantiated.
Why is nutrition research so messy?
Because of the limitations of RCTs, most food- and diet-related research is observational. The goal of observational research is to observe patterns in behaviors over time (such as “the impact of eating X amount of added sugar per day“). From here, researchers can draw associations between levels of intake with various health outcomes, most notably the development of heart disease, diabetes, etc. When conducting observational studies, researchers often look back in time, using medical records, participant self-report, and sometimes even blood samples, to collect information. Observational studies are super interesting as they help to identify any potential associations between our behaviors and our health. Though helpful, there are major limitations with observational research:
Limitations of nutrition research
The first is time. For practical reasons, an observational period is usually short: from a couple of weeks to a few years. Short studies make it difficult to draw statistically significant conclusions. In other words, were the associations true or did they happen by chance? The second limitation is relying on study participants to self-report their food intake. Can you remember what you ate on a Tuesday 3 months ago? Drawing conclusions based on self-report is very unreliable! The third is study design: who participated in the study? How may participants completed the study? For example, a study performed on men, ages 65-80, is not applicable to a group of adolescent dancers. And last is the potential for confounding variables.
Confounding variables are anything that could impact what is observed in a study. Examples include alcohol consumption and cigarette smoking. While researchers often use statistical methods to try to control for these confounding variables (for example, separating the participants who smoke versus those who do not smoke), it’s impossible to control for everything. Other confounding variables that can have a huge impact on health outcomes include socioeconomic status, race, and even degree of disordered eating.
Last, we should also consider how various studies define their variables. In regards to added sugar, Christy Harrison says, “In many studies, participants grouped as consuming the “lowest [amount of] added sugar”… consume an amount equivalent to eating some sweetened foods at every meal and every snack, and having dessert every day.” This is wildly different from how my fellow perfectionists often translate the research: “According to the research, I should “AVOID” or “ELIMINATE” foods with added sugar!” Nope, dancers, even the research shows us that it’s not all-or-nothing!
The impact of disordered eating on nutrition research
Since the definition of “disordered eating” is so grey in a culture that normalizes food restrictions and dieting, it’s hard to define “normal eating.” As I mentioned in this article, it took me years before I knew that my “clean eating lifestyle” was disordered! Interestingly, disordered eating behaviors and weight cycling (a common result of restrictive dieting) have been associated with negative health outcomes, including diabetes. So, it’s nearly impossible to conclude specific health outcomes from “eating foods high in X” when we know that disordered eating could impede results.
For example, when looking at sugar consumption studies, any potential negative health outcomes could arguably be associated with excessive intakes of sugar during a “binge” cycle. And if that’s the case, then it’s safe to say that repairing one’s relationship with food might be a better takeaway.
How should we use nutrition research?
Despite the limitations of observationanecal studies, and the scarcity of reliable RCTs, there are two types of research that can help us in better understanding various nutrition- and diet-related claims.
Systematic reviews and meta-analyses examine larger bodies of evidence in comparison to only looking at one study. But even with these, results should be taken with a grain of salt since outcomes are oftentimes inconclusive. In regards to heart health, a 2018 review concluded, “To date, a lot of results obtained have produced few conclusions and sometimes, even contradictions.”
We need to remember that association doesn’t equate to causation. Any manipulation of the macronutrients is likely to result in some form of dieting/restriction or disordered eating. Eating “processed” foods or foods that contain saturated fat, added sugar, and/or high fructose corn syrup will not be the sole contributor to your overall health.
Beware of anecdotal research and bias
More than ever, self-proclaimed nutrition enthusiasts utilize personal experience as a way to push specific eating behaviors. These claims are not supported by evidence and should be taken with a grain of salt. Rsearch funding is another consideration. Studies will always disclose funding. While funding isn’t always problematic (in fact, it’s necessary for most researchers to do their work), bias often exists. For example, if a study that concludes “the benefits of vitamin XYZ” is funded by the brand who manufactuers vitamin XYZ, it’s understandable to question the reliability of those results.
Nutrition research has played a major role in topics around fat, sugar, food addiction, and processed foods. Check out these articles to dive more into these topics:
- Is saturated fat bad for me?
- Is sugar bad for me?
- Is clean eating healthy?
- Are processed foods unhealthy?
- Can you be addicted to food (or sugar?)
Quick note: Christy Harrison is a fellow dietitian who covers these facts and more in her book, Anti Diet: Reclaim Your Time, Money, Well-Being, and Happiness Through Intuitive Eating. I credit Christy to my education on the subject of detangling the confusion around nutrition research!