The information has grown, but we're yet getting fatter over time. Something other than ignorance must be driving the trend. In a National Bureau of Economic Research working paper written with Richard A. Posner, a federal appeals court judge affiliated with the University of Chicago Law School, Professor Philipson proposes a simple theory. People haven't changed they've always liked to eat high-calorie food and generally disliked strenuous exertion but incentives have. For starters, the cost of consuming calories has plummeted, thanks to productivity gains in agriculture and distribution.
Food is cheaper and more abundant, encouraging people to consume more of it.
But that's an old trend, and it doesn't fully account for recent weight gains. More important in recent years is that the cost of burning those calories has surged as work has become more sedentary. If you wanted an income, you engaged in manual labor. Today you pay to exercise, not so much in money, but in forgone leisure time. So if you want to spend time with your kids, you have a choice between that and going to the gym or running.