For every study that warns against the health perils of coffee, there’s another that points to Java as the key to longevity.
Really, if you pick any trendy food—wine, kale, chocolate—and search for its health effects, you’re bound to find mixed messages.
So what’s the deal? Why are nutrition studies so often unreliable?
The question was debated in a scholarly squabble this past month by nutrition specialist Christopher Gardner, Ph.D., and John Ioannidis, MD, DSc, who focuses on the accuracy and reliability of scientific studies. The two met to debate a controversial statement: Most studies on the effect of nutrition and diet are false.
Ioannidis, a nutrition study skeptic, believes that it’s true. Many nutrition studies, he said, are fraught with design errors: Participants are often not randomized and the data of the studies are frequently kept private. Perhaps even more problematically, large food industries have been caught offering financial incentives to scientists.
In such a setup, the survey data would likely be self-reported, which leaves room for bias and error, he pointed out. On top of that, the study would need to account for a slew of confounding factors, such as exercise, smoking and drinking habits—the list is extensive — to ensure that any outcomes are due to broccoli, and not something else. And while some studies do control for those extraneous factors, others do not, Ioannidis said.
Studies based on observational epidemiology also do not provide evidence to show that one thing caused another — they only correlate with a rise or fall of risk for a condition. Any conclusions drawn from the data are purely associational, which is not necessarily bad, but it leaves room for uncertainty, confusion and potentially misleading information, Ioannidis said.
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