New York’s soda prohibition won’t work

New York City Mayor Michael Bloomberg's brave and provocative new plan to prohibit sales of large soft drinks would seem to promote public health at minimal cost to residents. It looks like the kind of tough regulatory action the nation needs to combat an obesity epidemic that could make this generation of schoolchildren the first in centuries to have a shorter average life span than their parents.

As a physician who has written extensively about the unconscious forces that cause people to overeat, I believe governments should pursue bold initiatives to fight obesity. Unfortunately, though, Bloomberg's Big Gulp ban is a bad idea.

To understand why, it's useful to compare the proposed ban on large sodas with the trans-fats ban the city instituted several years ago. They share important features.

In both cases, the product in question is undeniably unhealthy. Trans fats are known to be more likely to cause cardiac disease than any other commonly used cooking oils.

And in both cases, restaurants can turn to alternatives. After the trans-fats ban, they were able to switch to other cooking oils, with no discernible deterioration in the flavor of their offerings. Should the large-soda ban go into effect, restaurants will be able to offer their customers smaller beverages without causing anyone significant harm.

Where the fat and soda bans differ, however, is in their coherence. Trans fats are a particularly odious class of substances, 80 percent of which are artificially manufactured and added to processed foods. By one estimate, a 2 percent increase in the intake of calories from trans fats increased the risk of heart problems by up to 23 percent. This dwarfs the dangers of other fats.

Before the trans-fats ban, the city's health department made earnest efforts to educate restaurants about the problem. But they were completely ineffective, because restaurateurs realized that the cost of making the transition to alternative cooking oils would leave them at a competitive disadvantage.

By banning trans fats in all restaurants, the city leveled the playing field, ensuring that all its restaurants would bear the costs of switching to alternative fats. And those costs were a small price to pay for the public-health benefits of the prohibition.

Coke, Pepsi, and the like are also artificially manufactured and processed. And they contain an undeniably harmful substance, too. But that harmful substance (now that Coca-Cola no longer contains cocaine) is sugar, and the sugar in Coke is no more harmful than the sugar in apple juice or a milk shake. This is understandably confusing to residents, who may wonder why New York is planning to ban large sodas but not triple-decker chocolate cakes, or why the 280 calories in a 24-ounce Coke are somehow worse for them than the 330 calories in a Starbucks peppermint mocha.

The success of most policies depends on public support. And incoherent policies are difficult for the public to embrace.

If Bloomberg were defending his proposed soda policy before the Supreme Court, the justices would be asking whether it has a "limiting principle" — a rationale that would help determine where the policy begins and ends. The soda ban doesn't pass this test.

If sugar is the culprit, the city's policies should go after that culprit wherever it is. That would require a more sweeping policy, such as a tax on all sugary products, not just Big Gulps. But most people would find such a policy hard to swallow.