Ezra hopes that more information would make us thinner:
Contrary to my statement yesterday, the government could certainly reduce obesity by fiat. They could ban vending machines and junk food from schools. They could force all restaurants with more than five locations to post caloric information on the menu. They could subsidize fruits and vegetables rather than grains, corn, and meats. They could orient food stamps and the Women's, Infant, and Children nutritional program towards healthier foods. All these moves would reduce obesity, though it's arguable by how much.
If you wanted my pick among them, it would be posting caloric content in restaurants. It's a bit rich to watch libertarians and associated anti-government types oppose a regulation that gives consumers more useful information. This, after all, is how markets are supposed to work best. Consumers have better information, can pursue their preferences in a more coherent manner, and the market can provide, adapt, and innovate in response.
Weirdly, this may not always be true--apparently Vernon Smith's team has found that adding more information to markets can make them work less well. Once you've realized the awesome blossom you want is 2,000 calories, you may decide it's as well to be hung for a sheep as a lamb. Indeed, most of the people I know who struggle with their weight are extremely good calorie counters, because they've been on so many damn diets.
But sure, it's worth trying, though I also worry that this will be a barrier to small firms expanding, and will tend to shift the market towards even more highly processed food where the calorie content can be accurately measured. The closer your food is to nature, the more it varies in nutritional content.
How many libertarians do spend a lot of time arguing against this requirement? Most libertarians I know are basically in favor of greater transparency unless the compliance costs outweigh the benefits. Certainly, I think the government should take an active role in making information as accessible as possible, and I don't get a lot of pushback on that from the libertarians I hang out with. It's the "everything not forbidden is compulsory" kind of regulation that we hate.