Let’s focus on one of the most vexing dietary issues: saturated fat. Some studies suggest that it increases the risk of cardiovascular disease, and others suggest that it does not. Why this apparent contradiction?
“Nutrition research is not well funded,” says David Jenkins, Canada Research Chair in Nutrition at the University of Toronto and St. Michael’s Hospital in Toronto. For this reason, nutrition research trials typically have only 70 to 120 subjects. “When you don’t have big enough numbers, that’s where things can go wrong,” says Jenkins.
Small studies don’t provide powerful results, so researchers repeat the same small study multiple times and then group similar studies together in what’s called a meta-analysis. “We pool the data and arrive at a medium-sized study and reliable results,” says Jenkins. “Without meta-analysis, we end up with “He said, she said.” »
So imagine a small study being repeated several times. A research team may discover something that contradicts commonly accepted science. They are the ones who are aberrant. When combined in a meta-analysis, it won’t really skew the results. But when presented as an independent study, it can provoke sensationalist headlines. This is when you need to remember that small studies that haven’t been replicated shouldn’t change your thinking on a given topic. Base your nutritional decisions on the weight of evidence, not the trend of the day.
This is also true for the saturated fat debate. Although there are certainly good studies which indicate that there is no link between saturated fat and heart disease, the overwhelming majority further evidence supports connection. Jenkins advises choosing more plant-based foods and reducing the intake of saturated fats from animal products.
Jason Riis, a cognitive psychologist and senior researcher at the Behavior Change for Good Initiative at the Wharton School of the University of Pennsylvania, says: “Of course, read the dissenting opinions and continue to review the evidence, but follow the opinion of the vast majority of experts on a scientific question is usually a very good bet to make.
It’s also easier to understand nutrition research when you know more about the types of studies scientists conduct. The gold standard for assessing cause and effect (for example, whether saturated fat causes heart disease) is the randomized controlled trial (RCT), in which participants are divided by chance into separate groups that undergo different diets. But it is not always possible to carry out RCTs because they are expensive and it is difficult for people to follow a strict diet long term.
Instead, researchers often rely on correlational studies, which don’t show cause and effect, but tell us whether two things are related in some way. A big problem in this research is controlling variables outside of what is being studied. With saturated fat, for example, researchers try to control for other factors like income or exercise, but can never account for all the variables.
Correlational studies leave more room for interpretation than RCTs – and when human nature kicks in, it can seem like advice is flip-flopping. “Even when scientists try to be objective, their existing beliefs can get in the way,” says Riis. Personal biases, funding sources, or pressure to succeed can unintentionally seep into a researcher’s work and influence results.
Another possible influence is social conformity. The need to fit in is powerful: Studies show that being ostracized from a peer group activates the same part of the brain that feels physical pain. “Researchers care about telling the truth in their area of expertise, but they also care about how their peers and audiences will value their ideas,” says Riis. “Some experts may also find themselves in a situation where they will feel like they look stupid if they back down or admit they are wrong.”
Researchers can overcome this problem through open dialogue with colleagues to see if there are points that all parties can agree on. Riis talks about a newer type of research called adversarial collaboration, in which researchers with opposing viewpoints develop a dual-hypothesis study together and agree on all variables.
Just as scientists must find a way to address their biases in nutritional research, so must laypeople. If you believe a certain idea is true – say that saturated fats are healthy – you are probably (unknowingly) searching for information that fits your point of view. You might also be influenced by nutritional advice from friends, family and Facebook.
You can try to overcome this problem by reading different interpretations of the same science and listening to arguments from all points of view. “If you really want to understand science, you have to keep thinking about it, read new evidence, talk to more people, and be willing to update your beliefs,” says Riis.
The next time you see a headline about a new study that seems to contradict nutritional standards, remember that these are the studies that get the media attention; the vast majority of nutritional research never goes beyond the confines of medical journals. Examine the story carefully. Determine whether it is an RCT or a correlation study, and whether it is a single trial or a meta-analysis. Look for possible biases on the part of researchers and yourself; also determine if the study was conducted by a reputable institution and if it was published in a peer-reviewed journal.
Finally, ignore “experts” who claim to be 100% sure of the science on a given issue. “It shouldn’t bother you if an expert is uncertain, as long as he or she can say, ‘Right now, we don’t have a completely definitive study, but the available evidence makes me about 80 percent certain that. . . “, says Riis. He adds: “Science is a process, not an outcome.”
Registered dietitian Cara Rosenbloom is president of Words to Eat By, a nutrition communications company specializing in writing, nutrition education and recipe development. She is co-author of “Nourish: Whole Food Recipes Using Seeds, Nuts, and Beans.”
