There are many reasons behind the doubling of America's obesity rate over the past 25 years. Foodstamp use is higher, jobs have become more sedentary, populations are more sprawled, etc.
But the biggest factor is the decline in smoking, according to a controversial new paper from NBER.
Professors Charles Baum and Shin-Yi Chou found that smokers were 7.8% less likely to be obese. The declining use of cigarettes in America explains 2% of the increase in Body Mass Index (which is a low number but larger than any other factor).
This jibes with various medical conclusions about smoking and obesity:
Cigarette smoking may affect weight by altering “insulin homeostasis, lipoprotein lipase activity, the activity of the sympathetic nervous system, physical activity, and preferences in food consumption” (Williamson et al., 1991; see also Wack and 5 Rodin, 1982, and Hofstetter et al., 1986). Further, cigarette smoking reputedly suppresses appetite and enjoyment of food (Stamford et al., 1986; Williamson et al., 1991).
It also creates a dilemma for policy makers:
No one recommends cigarette smoking (or higher cigarette taxes) as a means to combat obesity, although the cigarette smoking covariates have statistically significant effects in this study.
Here are some other factors in the rise of obesity:
Sedentary jobs, food stamp use and urban sprawl were also found to have contributed to American obesity. So did demographic factors like a growing population of blacks and Hispanics, who are more likely to be obese.