How Our Habits Would Need to Change for a Soda Ban to Matter

Will people actually consume less soda just because they can't buy it in one giant cup?

burgerking-615.jpgDenis Sinyakov/Reuters

Chatter is picking up again around New York's plan to ban sodas larger than 16 ounces as the city gathers for its first public hearing on the proposed measure. Today's debate will be followed by a vote on Sept. 13, which -- hooray! -- leaves us a whole extra month to bicker over the bill.

With any luck, at least some of that talk will be informed by new research appearing in the New England Journal of Medicine explaining exactly what conditions Mayor Bloomberg would need for a soda ban to work.

Critics of Bloomberg's proposal point out that the soda ban does almost nothing to prevent those who want large quantities of soda from getting large quantities of soda. Remember that the stricture prohibits "food service establishments" from selling sugary drinks in quantities larger than 16 ounces. Diet sodas, dairy-based products like milkshakes, and alcoholic beverages are exempt from the ban. Determined soda addicts can simply buy two 16-ounce Cokes to get 32 ounces.

True enough, but left to their own devices, humans tend to think inside the box. You wouldn't ask Pepsi to design, test, and field a whole new 26-ounce bottle every time you're in the convenience store trying to decide between a 20-ounce bottle and a one-liter bottle. You'll probably choose one or the other and go about your business. In much the same way, Bloomberg hopes that consumers will simply accept buying 16-ounce sodas as the new norm.

For every person who opts for a 16-ounce soda over a larger size, New York restaurants will theoretically see a slight drop in the number of calories their customers are getting from sugary drinks. To find out just how much of an effect the ban might have on calorie intake, researchers at NYU gathered fast-food receipts from four regional cities, along with data from two existing studies on fast-food habits. Next, they cross-referenced that data with nutritional information supplied by the fast-food companies themselves. That gave the scientists a chance to calculate precisely, down to the item, how many calories were contained in a given meal.

Then, armed with that big stack of actual purchasing decisions, the researchers ran simulations in which a percentage of those (anonymous) consumers were "given" smaller sodas instead of bigger ones. They set up hypothetical scenarios where 10 percent of customers bought the smaller size (16 ounces) and 90 percent bought the larger size (32 ounces), running the simulation 1,000 times. They repeated that process for different distributions, from 20 percent on up to 100 percent of customers opting for the 16-ounce sodas.

calories-615.jpgNEJM

What they found was that calorie consumption as a function of soda intake begins to come down when about a third of customers adhere to the soda ban instead of circumventing it by buying two sodas of a smaller size. Naturally, the more people that play by the rule, the bigger the general decrease in caloric intake from soda.

Here's the takeaway for New Yorkers (and Cambridge-ians, too): we no longer have to make assumptions about whether a soda ban would work based on ideological cues about freedom and the role of government in mandating nutrition. There's actual data now pinpointing the exact threshold between success and failure. As long as more than 30 percent of city residents accept the options they're given at the checkout counter, the share of calories they get from sodas is likely to drop. While that may or may not actually affect the overall health of New Yorkers, it would be a quantifiable win for Michael Bloomberg.

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Brian Fung is the technology writer at National Journal. He was previously an associate editor at The Atlantic and has written for Foreign Policy and The Washington Post.

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