Nutrition has been making headlines for the past few decades. And those headlines can make it difficult to eat healthily. In the 1970s, eggs were vilified because they were high in cholesterol. Research had shown that high levels of LDL cholesterol in blood were linked with an increased risk of heart disease and stroke, and we knew eggs were packed with cholesterol. But it turns out that most of the cholesterol in our bodies is made by our liver and doesn’t come directly from our diets. You can’t fit that kind of nuance into a headline.
The stereotypical problem with news covering nutrition, said David Klurfeld, a nutritional scientist with the USDA, is that studies not designed to answer specific questions are portrayed as though they do.
Observational studies touting the health benefits of coffee have been in the news recently. Researchers followed coffee drinkers and non-coffee drinkers and monitored when and how they died.
Observational studies like these are useful for identifying interesting trends, but they do not demonstrate cause and effect. To test whether coffee prevents a certain disease, the researchers would need to conduct a randomized controlled trial. In this type of experiment, volunteers (preferably hundreds of them or more) are randomly assigned to one of two groups. In this case, one that drinks coffee and one that abstains.
Only when multiple observational studies, randomized controlled trials and experiments in animal models or individual cells all point to the same answer do responsible scientists begin to draw conclusions about nutrition. The results of all of these studies taken together can help inform us about how to improve our diets.
Unfortunately, news can’t wait until a consensus is reached. So here are a few strategies you can use to identify which headlines you should pay attention to. First, make sure the study was conducted in actual living humans. Then, determine whether the study was observational or based on a randomized controlled trial.
Whether the news is reporting on an observational study or a randomized controlled trial, Dawson and Ludwig recommend applying the “sniff test.” Ask yourself whether the claims make sense with what you know of your own experiences and human evolution.
There are lots of dietary trends that don’t pass the sniff test. Consider the fat phobia that erupted about the same time eggs made the bad food list. Ludwig called the low-fat craze a “nutritional disaster” because it caused many Americans to give up things we now know to be exceedingly healthy, like avocados, nuts and full-fat yogurt, while reaching for sugar-packed alternatives. Claims that cutting any given food from our diets will cure us sound too good to be true because they are.
Most importantly, “don’t change your diet based on one study,” Klurfeld advised, especially if that study has a small effect or contradicts a whole lot of other studies.
So next time you hear that chocolate will help you lose weight, cocktails protect you from heart disease, bingeing on sugary fruit juices cleanses your liver, ancient grains like wheat are toxic, or an extra two cups of joe a day will make you immortal, ask questions. How strong is the evidence? Are there multiple studies saying the same thing? And does it pass your common-sense sniff test?
What we do know about nutrition comes from repeated studies with a variety of methodologies in large populations and with mechanisms tested in animal models that show the same thing: Eating lots of fresh fruits and vegetables is good for you. Eating a low-fiber, high-calorie diet packed with sugar and fat is bad for you. But that’s not new or news, so those studies aren’t going to make headlines.
Amid the headline mania, if you want some surefire dietary advice to hold onto, Klurfeld predicts “moderation and variety are the two nutrition rules that are never going to change.”