Is Diet Soda Worse than Regular Soda?

July 11, 2013

There was an interesting story in CNN Health yesterday about a group of medical experts that are suggesting that diet soda might actually have negative nutrition outcomes. This is of special interest to folks that follow the soda tax proposals that have been cropping up across the states in recent years, because these bills often propose to tax full-sugar sodas while exempting diet soda in an attempt to nudge consumers to sugar-free soda options. From the article:

Purdue University researchers reviewed a dozen studies published in past five years that examined the relationship between consuming diet soda and health outcomes. They then published an opinion piece on their findings in the journal Trends in Endocrinology & Metabolism, saying they were “shocked” by the results.

"Honestly, I thought that diet soda would be marginally better compared to regular soda in terms of health," said Susan Swithers, the report's author and a behavioral neuroscientist and professor of psychological sciences. “But in reality it has a counterintuitive effect.”

Artificial sweeteners in diet soda fulfill a person’s craving for a sweet taste, without the calories. But that's the problem, according to researchers. Think of it like crying wolf.

Fake sugar teases your body by pretending to give it real food. But when your body doesn't get the things it expects to get, it becomes confused on how to respond.


On a physiological level, this means when diet soda drinkers consume real sugar, the body doesn’t release the hormone that regulates blood sugar and blood pressure.

I’m not an endocrinologist so I can’t comment on the medical validity of these claims, but this development does tell us something about tax policy. Using the tax code to try to influence personal decisions (especially ones as personal as nutrition choices) is difficult because the science is always changing as we learn more about health. Meanwhile, blanket tax policies only promote one government-approved option, when there are many combinations that might work to achieve a healthy lifestyle.

This is especially important to remember as soda tax advocates try to present an image of a unified body of literature in favor of soda taxes, when in fact there is good reason to believe soda taxes will just lead consumers to substitute calories from other sources.

More on soda taxes.

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