The diet soda myth

You didn’t think I was going to let an Aaron Carroll Upshot post on “Five Reasons the Diet Soda Myth Won’t Die” go by without a post, did you?

There’s a decent chance you’ll be reading about diet soda studies until the day you die. (The odds are exceedingly good it won’t be the soda that kills you.)

The latest batch of news reports came last month, based on another study linking diet soda to an increased risk of early death.

As usual, the study (and some of the stories) lacked some important context and caused more worry than was warranted. There are specific reasons that this cycle is unlikely to end.

1. If it’s artificial, it must be bad.

People suspect, and not always incorrectly, that putting things created in a lab into their bodies cannot be good. People worry about genetically modified organisms, and monosodium glutamate and, yes, artificial sweeteners because they sound scary.

But everything is a chemical, [emphases mine] including dihydrogen monoxide (that’s another way of saying water). These are just words we use to describe ingredients. Some ingredients occur naturally, and some are coaxed into existence. That doesn’t inherently make one better than another. In fact, I’ve argued that research supports consuming artificial sweeteners over added sugars. (The latest study concludes the opposite.)…

5. We still don’t understand the limitations of observational studies

No matter how many times you stress the difference between correlation and causation, people still look at “increased risk” and determine that the risk is causing the bad outcome. For reporting on hundreds of thousands of people, observational studies are generally the only realistic option. With very few exceptions, they can tell us only if two things are related, not whether one is to blame for the other (as opposed to randomized control trials).

With respect to diet sodas, it’s plausible that the people who tend to drink them also tend to be worried about their weight or health; it could be a recent heart attack or other health setback that is causing the consumption rather than the other way around. But you shouldn’t assume that diet sodas cause better health either; it could be that more health-conscious people avoid added sugars.

Many of these new observational studies add little to our understanding. At some point, a study with 200,000 participants isn’t “better” than one with 100,000 participants, because almost all have limitations — often the same ones — that we can’t fix.

Dr. John Ioannidis wrote in a seminal editorial: “Individuals consume thousands of chemicals in millions of possible daily combinations. For instance, there are more than 250,000 different foods and even more potentially edible items, with 300,000 edible plants alone.”

And yet, he added, “much of the literature silently assumes disease risk” is governed by the “most abundant substances; for example, carbohydrates or fats.” We don’t know what else is at play, and using observational studies, we never will.

Okay, now back to my Diet Dr Pepper.

About Steve Greene
Professor of Political Science at NC State http://faculty.chass.ncsu.edu/shgreene

3 Responses to The diet soda myth

  1. R. Jenrette says:

    My life experience is that I become easily addicted to high sugar carbohydrates. That means that if I eat candy or cake or such I have immediate and continuing urges afterward to eat more of the same. This nags at me until I go back to my low carb, protein rich diet. After a couple of days, the nags go away.
    It seems there are people who don’t get nagged by a carb rich diet and good for them.I choose diet Pepsi to keep my sugar intake lower.

    • Steve Greene says:

      Yeah. It’s amazing the cravings that carbs create for more carbs. I can sometimes check it by counting calories, but it’s hard.

      • R. Jenrette says:

        I chew so much gum to quiet cravings that my dentist commented on how well developed my jaw muscles are. Thank heaven one or two of my muscles are in good shape.

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