Harvard researchers conduct a real-world test of soda taxes


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Another day, another study on soda taxes.

But this one isn’t based on mathematical models or unreliable food frequency questionnaires. This time, researchers at Harvard implemented a temporary soda tax in the cafeteria of the school’s Brigham and Women’s Hospital in Boston. Then they waited to see whether actual people changed their drinking habits.


It turns out that they did. During a four-week period when the price of a 20-ounce bottle of soda went up by 45 cents – which amounted to a 35% price increase – sales fell by 26%. Meanwhile, sales of bottled diet soda rose by 20%. (The researchers said they were unable to change the prices of fountain drinks, so those soft drinks were not subject to the tax.)

Prices for full-calorie soda went back to normal after the test period, but sales ticked back up only slightly. Then researchers posted fliers around the cafeteria that said:

‘Lose up to 15-25 pounds in one year and decrease your risk of diabetes by 1/2. Just skip one regular soda per day. For zero calories, try diet soda or water.’

Those fliers remained up for four weeks, but sales of bottled soda didn’t fall during that period – in fact, they rose slightly.

Finally, the researchers reinstated the 45-cent soda tax while keeping the fliers up for another four weeks. That cut into sales of bottled soda, prompting a 36% decline compared with the weeks before the prices first changed.

The researchers concluded that taxes can work – only the price increase had a statistically significant effect on sales of sugared soda. When the tax was in place, diners switched to diet soda and coffee; sales of water and fountain drinks stayed the same throughout the study.

The researchers also wondered whether people who skipped their usual sodas would reward themselves by buying more snacks and desserts, but sales of those treats didn’t change either.

Of course, there was no way to tell whether anyone actually lost weight – or reduced their risk of health problems like obesity and diabetes – as a result of the tax.

The results were published online Thursday by the American Journal of Public Health.

-- Karen Kaplan Become a fan of our Facebook page and get a steady stream of health- and medical-related news, musings and the occasional oddity.