McDonald's

Market researcher Techmonic estimates that fast-food and fast-casual restaurants get about 10% of their sales from carbonated soft drinks, the consumption of which has been declining for years. The market is also an important one for Coca-Cola, which controls 70% of U.S. fountain sales, the publication says.

Bloomberg's plan is stunning for the depth of its hypocrisy. For one thing, it would exempt convenience stores such as 7-Eleven, home of the Big Gulp. Maybe it's because the industry is on a tear. 7-Eleven said it plans to add at least 630 new stores to its U.S. and Canada roster by year end. The mayor's plan also exempts caloric beverages such as orange juice, cafe lattes and milkshakes.

The Center for Science in the Public Interest (CSPI) and other members of the so-called food police are hoping that Bloomberg's proposal will spark a national discussion about obesity. CSPI has long argued that raising taxes on soda will help lower obesity rates.  The non-profit released a poll today that found that 77% of Americans want calorie labeling at convenience stores and 81% favor having supermarkets provide calorie information for their prepared foods.

Bloomberg, CSPI and their backers reduce the complicated question of obesity to a simple question of good foods versus bad foods. It's basically a one-size-fits-all approach that sounds great in theory but in reality won't do much to make fat people thin. People, including me, become overweight and stay that way for a host of complex psychological, economic and, in some cases, medical reasons. If it were just a matter of eating right and exercising, everybody would be thin.

The evidence that providing calorie information causes people to eat better is mixed. A study published by the International Journal of Obesity earlier this year "found New York City's label law had little effect on the food children chose to order," according to Reuters. A British Medical Journal report said that New York's 2008 law, which required fast-food restaurants to post calorie counts on menus, caused people to make healthier food choices but did not reduce overall calorie consumption.

Though I agree that obesity is a public health crisis, I am skeptical that government can make people thin through taxation policies or nutritional nannying. Unless the U.S. Congress passes a national soda tax, which is unlikely, people will evade a levy by purchasing carbonated beverages from regions that don't charge it. Consumers will save a few bucks by making big-ticket purchases in places that charge lower sales taxes. They are supposed to declare these purchases, but most don't bother.

This is a question that comes down to the reach of government. The government can encourage people to eat right and exercise, but in the end, we all need to take responsibility for our own health.

Jonathan Berr is long Coca-Cola and McDonald's. Follow him on Twitter@jdberr.