Mayor Michael Bloomberg wants to ban sugary soft drinks larger than 16 ounces. He believes that by this measure he can reduce obesity. But plenty of evidence indicates that he will fail. The ban will inconvenience people and waste their time, but it will not make them thinner.
Bloomberg didn’t originate this type of idea. Public schools, which hold their students captive for much of their day, have tried a similar approach to making students lose weight. And some have gone further than Bloomberg’s limit on cup size and have banned such drinks completely. But even complete bans haven’t worked. Students simply drink more sugary drinks after school. According to an article in the Journal of Nutrition Education and Behavior analyzing data for Maine, “keeping such drinks out of teenagers’ reach during school hours may not be enough.”
Another study, published in the journal Sociology of Education, examined school bans of junk food and found the same result: “Whether or not junk food is available to them at school may not have much bearing on how much junk food they eat.”
There are many ways to eat or drink “too many” calories. Will Bloomberg’s ban push people to switch from large soft drinks to large milkshakes? What is next? Limits on portion size in restaurants? Police monitoring people’s behavior in their homes?
It is really very difficult to force people to live more healthily than they want. The federal government has mandated safer cars, but research has consistently shown that such mandates lead people to drive more recklessly. (See also this study from the Review of Economics and Statistics.) The number of accidents actually increases after safety features such as seat belts are mandated for cars. True, the occupants of a car are more likely to survive an individual accident, but generally the number of accidents increases by enough to offset the safety benefits. In addition, more pedestrians and bicyclists are struck by cars.
This finding also applies to NASCAR drivers. And bicyclists are more likely to get hit by cars when they wear safety helmets.
This phenomenon is so pervasive that economists have even given it a name: the Peltzman effect, after the University of Chicago economist who first discovered it in 1975.
And it hasn’t been noticed just for automobile safety and food. The effect has shown up in childproof medicine bottles, where the childproof tops result in parents’ storing medicine in places that children find easier to reach, thus offsetting the benefits of the tops.
Possibly most relevant for Mayor Bloomberg, Peltzman recently noticed the result again in research showing that even great medical breakthroughs have little long-run effect on mortality rates. One of the most significant medical breakthroughs in human history was the development of antibiotics and other anti-infective drugs. Today, people no longer face a high risk of dying from past scourges like scarlet fever or tuberculosis. But these health benefits were offset when people began taking more risks, which led to more accidents, or when they changed their diet and exercise habits.
But Bloomberg’s proposed regulations are worse than just ineffective. Some people simply find it convenient to buy a large drink and nurse it for hours. Soft drinks are cheap compared to the value of people’s time, so why not buy a little extra instead of having to stop later to refill the cup? Bloomberg sarcastically dismisses this point: “Your argument, I guess, could be that it’s a little less convenient to have to carry two 16-ounce drinks to your seat in the movie theater rather than one 32-ounce.”
New York City during Bloomberg’s tenure has been on a tear trying to regulate people’s lives: banning trans fats and mandating calorie labeling on food in restaurants, pressuring restaurants to reduce the salt in their food, and restricting outdoor smoking.
Michael Bloomberg isn’t the first to think that he could simply mandate that people lose weight. But like other central planners, he is going to learn, no matter how much he dislikes it, that people have their own desires about how to run their lives.