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."
Banning larger sizes is a visible and controversial idea. If it fails, no one will trust that the next big -- and perhaps better -- idea will work, because "Look what happened in New York City." It poisons the water for ideas that may have more potential.
Second, 150 years of research in food economics tells us that people get what they want. Someone who buys a 32-ounce soft drink wants a 32-ounce soft drink. He or she will go to a place that offers fountain refills, or buy two. If the people who want them don't have much money, they might cut back on fruits or vegetables or a bit of their family meal budget.
Who buys large soft drinks? It's not just the people who may have some disregard for their weight. It may also be the construction worker who buys a single drink and nurses it all day. It may be the family of three who decides to split a single drink to save money. Soft drinks are bought by one-third of the poorest 2 million New Yorkers, but only one-sixth of the richest 1 million -- those who prefer to sip their fruit smoothies and lattes without regard for the burden on the less affluent soda drinkers.