It's pretty hard to lose weight. A lot of evidence suggests that waist circumference is heritable, with as much as half the differences between individuals down to genes. But this genetic explanation probably doesn't explain social trends towards obesity; surely there haven't been enough generations of heavier people having more kids than less heavy people (do they even have more kids?)
The issue gets weirder when we discover that animals living in human environments are also getting fatter, even lab rodents eating controlled diets!
Whatever the explanation for the macro issue, it's refreshing to note that on the micro level, people are still responding to incentives. After a big 2002 anti-McDonald's judgement 26 US states passed rules making it much harder to sue fast food companies for causing your weight gain. After this, people seemed to take more responsibility for their own weight and health.
This finding comes from a new paper, "Do 'Cheeseburger Bills' Work? Effects of Tort Reform for Fast Food" (latest gated, earlier pdf) by Christopher S. Carpenter, and D. Sebastian Tello-Trillo. Here is the abstract:
After highly publicized lawsuits against McDonald’s in 2002, 26 states adopted Commonsense Consumption Acts (CCAs) – aka ‘Cheeseburger Bills’ – that greatly limit fast food companies’ liability for weight-related harms.
We provide the first evidence of the effects of CCAs using plausibly exogenous variation in the timing of CCA adoption across states. In two-way fixed effects models, we find that CCAs significantly increased stated attempts to lose weight and consumption of fruits and vegetables among heavy individuals.
We also find that CCAs significantly increased employment in fast food. Finally, we find that CCAs significantly increased the number of company-owned McDonald’s restaurants and decreased the number of franchise-owned McDonald’s restaurants in a state.
Overall our results provide novel evidence supporting a key prediction of tort reform – that it should induce individuals to take more care – and show that industry-specific tort reforms can have meaningful effects on market outcomes.
I'm not saying individual responsibility always works but maybe some of the blame for obesity is down to individual choice.