The growth of American waistlines, according to one study, can be attributed to two words: quit smoking.
According to "Socio-Economic Causes of Obesity" by Charles L. Baum, Shin-Yi Chou published by the National Bureau of Economic Research, 30 percent of American adults are obese, which is 100 percent more than there were 25 years ago. And although a number of factors can be attributed to the rise in weight gain, the authors report that quitting smoking has had the largest effect on obesity in the country:
We use 1979- and 1997-cohort National Longitudinal Survey of Youth (NLSY) data, which allows us to compare the prevalence of obesity between cohorts surveyed roughly 25 years apart. Using the traditional Blinder-Oaxaca decomposition technique, we find that cigarette smoking has the largest effect: the decline in cigarette smoking explains about 2% of the increase in the weight measures. The other significant factors explain less.
Business Insider links several other studies that confirming the expected weight gain associated with quitting cigarettes:
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).
Other factors taken into account with the study as "important influences on caloric imbalance" include employment, physical activity at work, food prices, density of restaurants, involvement in food stamp programs and the influence of urbanization.