How Bloomberg's Soft Drink Ban Will Backfire on NYC Public Health

The New York mayor defends his prohibition on sugary drinks with an appeal to science, but the very people who carried out the studies in question say he's misread their work.

coke-615.jpgJoshua Lott/Reuters

On June 1 -- National Donut Day -- New York City's mayor proposed a restaurant ban for any soft drink over 16-ounces. The hope is that by banning big drinks people will drink less and weigh less. He and others cited our research as the science behind the policy. Indeed, a dozen of our studies show when you randomly give people large sizes of food like popcorn and French fries, they overeat. Another of our cited studies showed that people ate 73 percent more soup when eating from a soup bowl that secretly refilled itself.

There's a critical difference between the lab and Lexington Avenue that the mayor's office didn't account for: when Joe the Plumber and Bob the Banker buy soft drinks, they buy the size they want. They aren't randomly forced to take a 44-ouncer when they really wanted a 12-ouncer. Moreover, their Coke or Pepsi doesn't magically refill itself. If that happened, they'd overdrink. Instead, most restaurants give us a choice of a small or large drink -- just as nearly every fast food outlet gives us a choice of small, medium, or large fries, and every movie theatre gives us a choice of small, medium, or large popcorn. People who want a little buy a little, and people who want a lot figure a way to get it.

Yes, we have found that when people are given larger portions, they do drink or eat substantially more. But to claim that these results imply that the ban will be effective is to ignore our larger body of work. In our experiments, subjects were given larger or smaller portions of food in a dining or party setting, where they were unlikely to notice portion size. It is exactly because participants weren't paying attention that we got the results we did.

The mayor's approach, however, overtly denies people portions they are used to be able to get whenever they want them. In similar lab settings, this kind of approach has inspired various forms of rebellion among study participants. For example, openly serving someone lowfat or reduced-calorie meals tends to lead to increased fat or calorie consumption over the whole day. People reason that because they were forced to be good for one meal, they can splurge on snacks and desserts at later meals.

We've dedicated our research careers to helping people eat better. Some of the ideas that have grown from our work and that we've actively promoted include contributing to Smarter School Lunchrooms, 100-calorie packs, and the 2010 Dietary Guidelines. In the interest of disclosure, we've never received money from soft drink companies, nor have we received money from the New York City Department of Health or Mayor Bloomberg's office to investigate a better solution. We fear, however, that the proposed ban will be a huge setback to fighting obesity for two reasons: 1) unless it succeeds, it will poison the water for better solutions, and 2) it won't succeed.

First, consider the McLean Effect: McDonald's launches the visible and controversial low-calorie hamburger; it fails, becoming a cautionary byword for restaurants for the next 15 years, when no one dared introduce low-calorie fast food offerings because "Look what happened to the McLean."

Presented by

Brian Wansink & David Just

Brian Wansink (Ph.D.) is the John S. Dyson Professor of Applied Economics at Cornell University and the author of Mindless Eating: Why We Eat More Than We Think. David Just is an associate professor of economics at Cornell University.

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