The percentage of Americans who are considered clinically obese began to rise dramatically in the 1970s — climbing from 14 per cent to 30 per cent. Interestingly, the 1970s is also when the US began taxing cigarettes. Are the two related?

Some scientists now suspect that’s the case. After all, nicotine stimulates your metabolism, which is why many people who quit smoking begin to gain weight. As taxes on cigarettes rose — driving the price from 63 cents in 1980 to $3.37 today — tons of people quit. (Economists estimate that for every 10 per cent rise in cigarette prices, 5 per cent of smokers quit.) As Daniel Gross reports in today’s New York Times:

In a 2004 study, [City University of New York economic professor Michael] Grossman, along with Shin-Yi Chou of Lehigh University and Inas Rashad of Georgia State, mined state-by-state behavioral surveys from 1984 to 1999 to get to the root causes of rising obesity. While they found that the prevalence of fast-food restaurants was responsible for most of the climb, they concluded that the decline in smoking accounted for about 20 percent of it. Over all, they found that “each 10 percent increase in the real price of cigarettes produces a 2 percent increase in the number of obese people, other things being equal.”

Mind you, as Gross reports, some academics dispute these findings, and claim any increases in weight are only short-term.

But if Grossman were right, it would raise an interesting question. Given the relative morbidity rates of diseases caused by smoking versus diseases caused by obesity, is there an optimum price for cigarettes — i.e. a price at which it discourages the most amount of people from smoking, while creating the smallest possible new population of obese people? I’d love to see that math.