Bloomberg bans large-sized soda: The science behind the decision.

The NYC Soda Ban Just Passed. Will New Yorkers Actually Lose Any Weight?

The NYC Soda Ban Just Passed. Will New Yorkers Actually Lose Any Weight?

The state of the universe.
Sept. 13 2012 1:15 PM

Fuzzy and Fizzy

The contested science behind Bloomberg's ban on large-sized sodas.

NY Mayor Michael Bloomberg as a nanny
The Center for Consumer Freedom ran an ad of New York Mayor Michael Bloomberg as a nanny in protest of his proposed plan to forbid the sale of sugary drinks larger than 16 ounces

The New York Board of Health passed a rule prohibiting the sale of large sodas on Thursday. The ban, masterminded by Mayor Michael Bloomberg, has provoked strong feelings for and against it, especially because the science linking sugary drinks to obesity seems so murky. In June, award-winning author Dan Engber dove into the conflicting studies surrounding the controversial rule. His original piece is printed below.

Daniel Engber Daniel Engber

Daniel Engber is a columnist for Slate

 "What's next?" asks the industry-funded Center for Consumer Freedom, in response to a New York City plan to forbid the sale of sugary drinks larger than 16 ounces in restaurants, sports venues, and movie theaters. "Limits on the width of a pizza slice, size of a hamburger or amount of cream cheese on a bagel?" Mayor Michael Bloomberg defended his idea Friday, assuring Matt Lauer of the Today show that "we're not banning you from getting the stuff. … It's just if you want 32 ounces, the restaurant has to serve it in two glasses. That's not exactly taking away your freedoms."

It didn't take long for the details of this putative public-health measure to dissolve into a super-sized debate between Libertarians and Liberals, soda jerks and health nuts. But before we all start pouring it on about the costs of obesity and an apartheid of pleasure, let's consider the scientific facts—contested or otherwise—that led Bloomberg to propose his soda-size control in the first place. Would the pint-cup cutoff reduce obesity, or not?


There are two questions here, both of them well-studied by nutritionists and epidemiologists. First, would people eat or drink less if they were served in smaller portions? Second, would they lose weight if they consumed less sugary liquid?

The answers seem obvious to most people: yes and YES! That’s part of what makes it so hard to study the questions. Since we already think that both super-sizing and soda make us fat, the people who avoid super-sized portions and nondiet soda tend to be the same ones who join the gym, eat fish twice per week, and natter on about the joys of kale. These health-conscious people also tend to have money, and given that obesity and poverty are related in all kinds of ways, it's tricky to determine which parts of an obesogenic lifestyle might count the most.

Tricky, but not impossible. There are plenty of data, for example, to show that portion sizes have increased over the last 30 years while childhood obesity rates tripled. For a 2011 paper in the Journal of Nutrition, Carmen Piernas and Barry Popkin used national surveys to study the diets of more than 30,000 kids and measure how their junk-food habits changed from 1977 to 2006. They found that soft drink portions had increased by almost one-third. (Once upon a time, a "king-size soft drink" was just 12 ounces.) But sodas and fruit drinks weren't the only foods that swelled: The energy content of cheeseburgers increased by almost one-quarter, pizza slices jumped by 35 percent, and portions of Mexican food by even more than that.

We know that kids got their junk food in bigger portions in the 1980s and 1990s, and that they got fatter overall. But what's the rationale for singling out the jumbo soft drinks for government oversight, as opposed to the double-wide pizza and 10-inch burritos? That's where things get interesting—provided you're interested in contentious science, slippery datasets, and the connivings of shady technical consultants.

The case against soda starts with the idea that the body’s response to beverages differs from its response to solid food. People regulate their caloric intake without thinking. If we eat more at one meal, we'll go lighter on the next. But for some reason (the mechanism is still unknown), drinks throw this compensatory mechanism out of whack. A sugar-sweetened beverage might give you as much energy as a candy bar or a heap of mashed potatoes, but you'll be less inclined to account for it with tempered eating down the line.