Rob Brooks has posted an article (also published in The Conversation) outlining his argument that the relatively cheap price of carbohydrates compared to the price of protein is driving the obesity crisis. Drawing on material from his book Sex, Genes and Rock ‘n’ Roll: How Evolution Has Shaped the Modern World, Rob argues that as our recent evolutionary history involved a diet of lean meat and high fibre plant foods, modern humans are poorly evolved for the cheap simple carbohydrates that dominate many modern diets.

I have considered Rob’s arguments and policy suggestions in an earlier post, but there is one element in Rob’s post that I would like to discuss. At the end of his post, he writes:

New York’s mayor, Michael Bloomberg, infuriated civil liberties groups and the sugar and soda lobbies last October when he asked the US Department of Agriculture to allow New York City to ban the 1.7 million citizens who receive [food stamps from using them to buy soda](http://www.nytimes.com/2010/10/07/nyregion/07stamps.html?_r=1).

Those Americans poor enough to receive food stamps are precisely the people most at risk of obesity: people with enough access to food that they do not starve, but not enough money to eat a healthy diet with plenty of protein.

So did Mayor Bloomberg have the right idea? Should we tell people what they can and can’t eat or drink? Libertarians love to tell us that we have a choice, and that nobody is forced to overeat.

Despite describing myself as having libertarian leanings, I don’t think this is a bad idea. Bloomberg is not telling people what to eat or drink. If the food stamp users wish to consume sugary products using their own resources, they are free to do so. Similarly, they cannot buy cigarettes with food stamps, but they are still free to smoke.

I usually extend this idea across any provision of government services. While I would often prefer that they were not provided to begin with, placing conditions on access is not restricting liberty as long as the option to take action as a private citizen remains. If the conditions become tight enough, the government service disappears altogether (not that I am arguing that is what should be done with food stamps).

So, controlling use of food stamps among a group most vulnerable to obesity might be a good place to start. However, what I would like to see are some random trials of controlling food stamp expenditure. While state by state comparisons will produce some useful evidence, a random trial would give some evidential meat to the argument that restricting access to sugar will work in practice.