The Press Fans Overblown Fears About Diet Soda—Again

By Elizabeth Nolan Brown of Reason.

""I have never seen a thin person drinking Diet Coke," tweeted Donald Trump, himself a frequent consumer of diet soda, back in 2012. Besides being an amusing self-own, Trump's comment helps explain the trouble with most research on diet drinks—including a new study that's been making the media rounds this week. 

"It doesn't matter if it's sugary or diet: New study links all soda to an early death," reported The Washington Post on September 4. It was one of many similar headlines. The implication of all of them was clear: Zero-calorie cola is a big fat lie, and if you don't ditch it now you're staring down a premature grave.

But let's back up. Here's what the paper in JAMA Internal Medicine actually found about drinks containing artificial sweeteners: People who consumed two or more per day were slightly more likely than those who abstained from all soda to die from diseases related to circulatory problems.

(Consuming one or more sugar-sweetened soda per day, meanwhile, was associated with increase risk of dying from liver, appendix, pancreas, and intestinal diseases.) Whether these circulatory problems are directly related to diet soda is unknown—and there are good reasons to suspect they are not.

"Researchers cautioned that elevated soft-drink consumption may be a marker for an overall unhealthy lifestyle," the Post points out. That is, people who consume sodas daily may also be more likely to eat out at restaurants, consume processed snacks, or engage in other dietary habits that up their disease risk.

Alternately, people who don't drink soda at all may be more likely to engage in some behaviors—drinking more water, say, or consuming other nutritious beverages—that accrue them disease-protective benefits.

And while all sorts of people drink diet soda, it tends to be especially popular among people actively trying to lose weight and/or to give up a non-diet soda habit. Which is to say that diet drink consumers could (as that Trump tweet suggests) be heavier to begin with, or could share some other quality (such as previously high consumption of sugary drinks) that sets them up for future health problems.

The scientist behind this study tried to account for some confounding factors, such as smoking and obesity. But accounting for all lifestyle differences is impossible. Here's what the lead researcher, Neil Murphy, told the Post:

We recognize that a possible explanation for the positive associations found for artificially sweetened soft drinks is that participants who were already at greater health risk (those who were overweight or obese; those with prediabetes) may have switched to artificially sweetened soft drinks to manage their calorie and sugar intake.

Even the notoriously pro-nanny-state Center for Science in the Public Interest urged caution about the latest research. "This new European study is somewhat inconsistent with earlier findings," the group's director of nutrition told the Post.

That's true: Several meta-analyses last year found no association between drinking diet soda and weight gain or increased body mass index. Those studies also found no association between aspartame (the most common artificial sweetener) and negative effects on heart-disease risk factors, fat levels, or metabolic issues."