Eat this, don’t eat that. Diet trends come and go based on what the current nutritional studies show and what happens to be hot at the moment. You’ve probably noticed studies focused on nutrition don’t always agree with each other. One may show a low-carb diet is best for weight loss and the next proclaims a diet low in fat as best for melting away the pounds. Then throw Paleo and gluten-free into the mix to further add to the dietary chaos. Is it any wonder that people are confused about what they should eat? The reason nutrition studies are so conflicting and hard to make sense of boils down to four main reasons.
Nutrition Studies Are Hard to Conduct
The “gold standard” study is one called a randomized, double-blind, controlled trial. With this study, one experimental group is exposed to a variable, in this case, a particular type of diet or supplement, and the other is not. The second group serves as a control group. The participants are randomly assigned to groups and don’t know whether they’re in the treatment group or the control group. Everything is carefully structured and controlled.
You can imagine how hard this type of study is to carry out in real life. You’re asking people to stick to a particular diet for a period of time and monitor everything they eat. It’s not as hard to do this with a medication where one group takes the medication and the control group takes a placebo pill – but with diet, it’s a real challenge! Are you going to ask the participants to stay in a clinic or hotel where you can make sure they don’t cheat? Not very practical.
Because randomized, double-blind controlled trials on nutrition are hard to carry out, scientists mostly do observational studies. With these studies, researchers follow people who eat a certain way over time to see if some outcome, like weight loss or the risk of some disease, differs in these people relative to those who don’t eat that type of diet.
For example, you might follow people who eat a vegetarian diet over a 10-year period and compare them to people who eat a standard American diet to see who develops more heart disease. While this study is easier to conduct, it has limitations. For example, vegetarians have other characteristics that might impact their risk for heart disease. People who eat a vegetarian diet might be less likely to smoke and more likely to exercise etc. Sometimes you can control for these factors if you’re aware of them, but some studies don’t do an adequate job.
People Can’t Remember What They Ate
Another problem with nutrition studies is they often rely on food questionnaires or ask people to remember what they ate or how often they eat a certain type of food. A classic example is the food frequency questionnaire where researchers ask participants to list how many times a week they eat a certain food. That’s a toughie! Most of us have a hard time remembering what we ate two days ago, much less what we ate a week ago.
Some nutrition studies even ask participants to recall what they were eating ten years ago! How accurate are those results likely to be? Plus, people like to present themselves in a favorable light. If they thought they SHOULD have eaten more vegetables, they might fudge a little and say they ate more. All in all, most folks aren’t very good judges of how MUCH they eat OR how many calories they expend exercising. Plus, there’s a natural tendency to portray ourselves in a positive light.
Genetic Differences
Another factor that makes it hard to draw solid conclusions from nutritional studies is the fact that people differ genetically and hormonally. If you’re a person with poor insulin sensitivity, you’ll likely have a different response to a low-carb diet than someone with good insulin sensitivity.
Partially because of this, the field of personalized nutrition will likely become a force in the future. There’s growing awareness that individuals respond differently to food based on their individual genetics and the type of gut bacteria they have in their intestines to process that food.
Plus, not all food is the same. Foods grown in certain types of soil or ones that are genetically modified or grown organically may differ nutritionally. In other words, one apple can be more nutritious than another. Not only can this alter the results of the study, since you can’t control for all of these factors, but it means the results might not apply to you if you differ genetically from the participants in the study. Fortunately, one day, you’ll be able to get personalized diet recommendations based on your genes.
Some Studies May Be Biased
You may have noticed some studies are sponsored by particular industries. For example, the dairy industry sponsors nutrition research. Not surprisingly, these studies often show favorable results that place the dairy industry in a positive light. Some studies are also sponsored by corporations like Coca-Cola or Nestle. Interestingly, the results that come out of these studies are often more favorable than the results from studies that aren’t corporate sponsored.
The Bottom Line
Now you have a better idea of why nutrition studies lead to conflicting results. That’s why you shouldn’t jump on every study that comes out and take the results as gospel. Even more important, don’t change your diet based on the results of a single study. Know who sponsored the research and, even then, take the results with a grain of salt.
Only when you begin to see lots of well-conducted studies showing the same thing does the finding have more credibility. For example, a number of studies show the Mediterranean diet has health benefits. Plus, common sense tells you that a diet that emphasizes unprocessed foods with lots of fruits and vegetables is good for you.
The take-home message? Don’t ignore nutrition research but don’t take it as gospel either. You can’t go wrong eating more whole, unprocessed foods.
References:
Journal of Business and Psychology. 17.2 (2002) Accessed on 10 March 2011.
UniteforSite.org. “The Challenges and Failures of Nutrition Studies”
Eater.com. “Why Corporations Make it Hard to Trust Nutrition Studies
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