Call it the war on supersizing. Mayor Michael Bloomberg wants to restrict the size of New Yorkers' soft drinks. He's been on the vanguard of public health policy before, with a 2002 indoor smoking ban and a trans-fat fight in 2006. Later efforts -- including an attempt to restrict food stamp recipients' ability to buy sugary drinks and a failed soda tax -- have been decidedly less successful.

There are logical governance reasons for this nanny-state meddling. Obesity is a major health issue, and New York State has one of the costliest health-care burdens per person in the United States. Controlling obesity would help control out-of-control health-care spending, or so the argument goes. However, banning soda may be the wrong way to rein in rising obesity rates and control out-of-control health-care spending -- but not for the reasons you might think.

Don't tread on my waistline Americans love their freedom of choice. Many were vocal on the issue after news broke of Bloomberg's soda crackdown. "How dare the government infringe on my right to suck down an entire toilet tank's worth of high fructose corn syrup?!" they cried. What most failed to realize is just how influential the government really is on its citizens' health choices, directly and indirectly. It's the indirect influence that I'd like to talk about. The source of our modern obesity epidemic, a plague of cheap corn, can largely be laid at the government's feet.

The cost of commodity corn ranged near $2 per bushel for decades before its recent spike, and about 10% of that cost was subsidized by direct government payments to farmers. From 1995 to 2009, corn farmers received an average of $5.3 billion a year in direct and indirect subsidies. That amounted to about $0.48 of total subsidies per bushel of corn in 2005. In this last "cheap" year for corn, subsidies made up a quarter of corn's total commodity price.

Michael Pollan explains the history and effects of the American government's role in corn production with far more depth and detail than I ever could. The best distillation of his why-we-eat-what-we-eat best-seller, The Omnivore's Dilemma, is this: "When food is abundant and cheap, people will eat more of it and get fat." And corn, easy to grow, easy to store, and extremely nutrient-dense, makes an ideal starting point for all manner of inexpensive byproducts.

Amber waves of really cheap grain Modern American agricultural policy goes back to the early '80s, when major grain buyers Cargill and Archer Daniels Midland (NYSE: ADM) began to directly influence the language of congressional farm bills. Commodity corn has been sold at the same low levels, roughly $2 per bushel, ever since, with the exception of a wide-ranging commodity price spike that began in 2007. The primary reason for this recent price increase is a massive surge in exports to China, which means we're now effectively subsidizing a future Chinese obesity crisis, too. Still, the cost of commodity corn remains only a small part of our final food costs.

Cheap corn has made its way into about a quarter of the groceries found in most supermarkets, almost all of it processed. A box of cereal is worth about $0.08 to farmers. It's "magically delicious" thanks to science, not farm labor. The industrial-scale mass production of cheap meat is possible because there is always enough cheap corn for feed -- over a hundred million tons of the stuff is gobbled up by farm animals each year.

The hidden health costs of corn American waistlines were largely under control before the plague of cheap corn. Obesity trends changed very little from 1960 to 1980, but from 1980 to 2000, American obesity rates doubled. In 2010, more than 78 million adults, and 12.5 million children, were obese. This obesity epidemic costs the country about $190 billion a year, or 21% of all health-care spending, according to a Cornell University study released earlier this year.

People who choose to drink that jumbo Slurpee do affect you when you pay higher taxes for Medicare and Medicaid. These programs combined to cover 93 million people in 2010, and it's worth noting that the poor and elderly are more likely to be obese than the general populace.

A chart put together by my colleague Morgan Housel shows the impact cheap corn has had on the nation's youth, though he might not have intended it to:

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Big Government, Bad Policy, and Rising Health-Care Costs