Yes, yes, we’ve all heard about how those awful, nasty, fast food restuarants are making us all so fat we’ll keel over from the cholesterol before we hit 35. Even that this generation will be the first in modern times to live shorter lives than their parents. That the NHS is about to buckle under the weight of lard butts demanding treatment so we must immediately impose the Big Mac Tax.

The problems with this narrative are numerous: not least that people dying young from being porkers saves the tax system money, not costs it. But the first question we really need to ask ourselves is, is it true that fast food restaurants, or indeed restaurants of any kind, actually lead to the observed increased whaleness of the nation’s shape?

While many researchers and policymakers infer from correlations between eating out and body weight that restaurants are a leading cause of obesity, a basic identification problem challenges these conclusions. We design a natural experiment using highways in rural areas to exploit exogenous variation in the effective price of restaurants and examine the impact on body mass. We find no causal link between restaurant consumption and obesity. Analysis of food-intake micro-data suggests that consumers offset calories from restaurant meals by eating less at other times. We conclude that regulation targeting restaurants is unlikely to reduce obesity but could decrease consumer welfare.

Well, no, it appears that the restaurants aren’t in fact the problem. After gorging at a restaurant we all seem to eat less next time, when not at a restaurant. Meaning that our targetting of those restaurants won’t in fact cure whatever ills we diagnose as coming from the undoubted rise in weights that is going on.

Meaning also that the problem lies elsewhere: but good luck to the government that tries to deal with that. There aren’t all that many votes in saying “You’re fat because you’re greedy” now, are there?