Why Diet Soda Should Be Taxed, Too

| Fri Jun. 22, 2012 5:00 AM EDT
A whole wall of Diet Coke.

Sugar-free diet soda has gotten a free pass in the recent debates on soda regulation, covered in Monday's Econundrum. Proponents of soda bans or taxes have attacked Big Gulps and other giant drinks sweetened with sugar or high fructose corn syrup, but DIET COKE devotees may want to hold off on gloating. A new study found that diet soda drinkers had altered brain responses to saccharin (Sweet'N Low) compared to nondrinkers.


Researchers at the University of California-San Diego and San Diego State University recruited 24 participants, half of whom drank diet soda regularly, and imaged their brains responding to a squirt of water flavored with saccharin or sugar water. Artificial sweeteners taste sweet, but they don't quite taste like real sugar. Researchers using fMRI, an imaging technique that tracks blood flow in the brain, see a different response to sugar than to sweet substitutes like sucralose (Splenda) and, in this study, saccharin.

In diet soda drinkers, however, the right orbitofrontal cortex of their brains could no longer distinguish between real sugar and fake sugar. In addition, there was decreased activation in an area called the caudate head. The more often the participants reported drinking diet soda, the less activity in this brain area, and the study authors had previously linked decreased activation in the caudate head to obesity.

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This is a small-scale study, and it's far too early to say that diet soda makes you fat. Bedeviled by confounding factors, observational studies tracking obesity in diet soda drinkers have come up with conflicting results. But a controlled study in rats from 2010 does suggest a link between diet soda and obesity. Rats fed saccharin-sweetened yogurt ate more rat chow, gained more weight, and had more body fat than those who got the same amount of yogurt with a natural sugar, glucose, instead. This new fMRI study is a nice follow-up that begins to extend the story in humans. Further research into other sweeteners like aspartame, most commonly found in diet soda, is needed too.


Many high fructose corn syrup manufacturers also make artificial sweeteners.



In the end, everybody is a probably little bit right: Drinking one can of soda, whether diet or regular or Mexican Coke, isn't going to kill you. Drinking them all the time might not be so great.