One of the things that economists like to ponder is whether things are substitutes or complements. For example, we know that both smoking and obesity are unhealthy, too much of either does tend to kill.
However, do obese people smoke more than thin people? Does one unhealthy habit lead to another that is? Or do people tend to be only one of the two, either smokers or obese?
We’re interested of course because we’d like to aid people in making themselves healthier. Our method of doing this might well be different dependent upon whether these habits replace each other, are substitutes, or encourage each other, are complements.
To be trivial, if people do both then we might put the donut shop a couple of miles away from the tobacco store: make it difficult to do both. If substitutes, put the stores right next to each other, so that people will choose the one.
It turns out that, while some are both smokers and obese and some are neither, the two are, on average, substitutes.
Another way to look at it is that nonsmokers in the highest social class have a higher rate of obesity (13.3%) than smokers in the lowest social class (13.1%). Rates of severe obesity—which is a condition popularly associated with the underclass—is actually more common amongst the highest class of nonsmoker than the lowest class of smoker. No matter which class you look at, obesity rates are always higher amongst nonsmokers.
No, it’s not just that all the smokers are dead and therefore cannot get obese. Nor is it just that people do choose one or the other. It’s that nicotine, as a stimulant, reduces obesity.
This does not mean that everyone should go smoke to avoid getting fat. The health risks from smoking are higher than those from being obese. However, given that it is (at least partially) nicotine which is having the weight reducing effect:
The second point to consider is that since nicotine is an aid to maintaining a healthy weight, why are alleged health campaigners banning products like snus and e-cigarettes which not only get people off cigarettes but could control their weight as well? If smoking and obesity really are the two greatest public health threats of our time, doesn’t that make ultra-low risk nicotine products the penicillin of the age?