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Diet Coke on ice
AP File Photo/Wilfredo Lee
You’ve heard it before, and you’ll hear it again: Diet sodas may mess with metabolism.

Did you get the full story about artificial sweeteners and diabetes?

By Svati Kirsten Narula

A study published in Nature this week provides evidence of a link between artificial sweeteners and diabetes, and the media is all over it. “Artificial sweeteners may disrupt body’s blood sugar controls,” wrote the New York Times; “Diet soda may alter our gut microbes and raise the risk of diabetes,” reported NPR.

As a science journalist myself, I considered writing something about the study, too. But the research, while noteworthy, didn’t strike me as particularly new or exciting. That’s partly due to the fact that I’ve read about other studies investigating the potentially harmful effects of artificial sweeteners. It’s also because of personal experience.

In 2008, I was a volunteer subject in a clinical trial investigating whether artificial sweeteners provoke metabolic responses similar to the effects of real sugar—the same big question posed by the study that came out this week—at the National Institutes of Health. Nine people with Type 1 diabetes (including me), 10 people with Type 2 diabetes, and 25 people without diabetes underwent an experiment in which we drank artificially-sweetened diet soda followed by a carbohydrate-rich shake one day, and on an alternate day we drank unsweetened seltzer with the shake instead. Our gut hormones and blood sugar levels were monitored closely on both days.

The study found that ingesting acesulfame-K- and sucralose-sweetened diet soda in addition to carbohydrates, the same way someone might drink a diet coke while eating french fries and a burger for lunch, led to an increase in an insulin-regulating hormone in healthy subjects and those with Type 1 diabetes. It was almost as if our bodies thought we needed more insulin when we consumed diet soda with our food.

Scientists at NIH have continued to investigate the effects of sugar substitutes on blood glucose and the endocrine system. In other studies, they’ve found that consumption of diet soda is associated with statistically significant increases in insulin production in some subjects and markedly higher blood sugar levels in subjects with Type 2 diabetes. Kristina Rother, one of the principal investigators on these studies, says the results support the hypothesis that artificial sweeteners induce insulin resistance—a condition associated with Type 2 diabetes and obesity.

“Things don’t have to be shocking and new to get this shocking and new treatment.”

Rother points to her colleague Susan Schiffman as one of the first to show that artificial sweeteners affect gut bacteria in rodents—research (PDF) that created a stir when it was published in 2008. Years earlier, Schiffman had been quoted alongside David Katz, from Yale, in a 2005 New York Times article questioning the safety of Splenda.

There have been a lot of major news stories about the science behind artificially sweetened products. But I didn’t see a single one this week that acknowledged the ones written earlier this year, or in 2008, or 2005.

More often than not, each individual story gives the impression that the latest science is either totally new or surprisingly compelling. “It seems to amplify every time,” Purdue University’s Susan Swithers told Quartz. “Things don’t have to be shocking and new to get this shocking and new treatment.” Swithers herself has been featured in news stories about artificial sweeteners and diabetes, including an NPR one asking “Do diet drinks mess up metabolisms?” in 2013.

Not many news outlets have the space, time or resources to contextualize, at length, each meaningful scientific study. But there’s something wrong with a cycle in which reporters constantly react to press releases from academic institutions or scientific journals by generating uniquely attention-grabbing stories based on each one.

Virginia Hughes, a contributing editor at Popular Science, points to the numerous articles that have been written about resveratrol (the oft-heralded compound in red wine) as an example: Each piece is accurate and fair, but in aggregate they’re a jumble of contradictions. And they don’t reference each other—there’s little acknowledgment, in each bit of reporting, that other reporting has occurred on other studies and that this jumble of contradictions exists. “Should we switch to a more explanatory, wiki-like model, so that a single study’s results are more fully contextualized?” Hughes wonders. “Should we be writing stories about batches of studies — maybe the last 10 studies of resveratrol, as opposed to the single newest one?” (To that, I say yes, please: This is the time and place for those card stacks and continuously-updated posts at Ezra Klein’s Vox.)

And while a journalist may describe the details of the science correctly—“the researchers analyzed the blood-sugar levels and gut bacteria colonies of 381 participants”—his or her story, taken on its own, doesn’t give readers an accurate representation of how scientific research works. Science is slow; it takes baby steps, and what may look like the “first” piece of evidence about something is usually more like the tenth or twelfth. Former Washington Post reporter David Brown explained this eloquently in a 2008 speech at the University of Iowa (you can read the full text here):

We in the media live in a time of incredible competition for readers’ attention—from television, radio, magazines both real and online, the gigantic blogosphere, and sometimes even our own websites. At the same time, getting on Page 1 is almost all that counts. It has always been important.

Science stories, and especially medical stories, have a really good shot of getting out on Page 1. They are inherently interesting and they appeal to what might be termed, somewhat cynically, as the narcissism of the reader. But that often isn’t enough to get them on the front page. To get there, the story must emphasize novelty, potency, and certainty in a way that, as a general rule, rarely exists in a piece of scientific research.

The Nature paper is a well-done, illuminating bit of research, and it’s a great addition to the cumulative work of other scientists, including Swithers, Rother, and Schiffman. Downplaying the “cumulative” part of the story, though, does a disservice to readers—even well-informed ones. Nutrition expert Marion Nestle recently blogged about the Nature study and expressed some skepticism about the fact that the bulk of the research was done on mice. But larger trials have been done on humans and the NIH is about to start another human trial to see what happens when a bunch of healthy “non-users” of artificial sweeteners start eating sucralose. That’s information that most major media outlets failed to mention in their articles about this study.

Perhaps they just didn’t have the time.