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Article Excerpt
I. INTRODUCTION
Two of the most notable trends in public health over the past 30 yr are the reductions in smoking rates and the rapid increase in obesity rates. Based on data from the National Health Interview Survey, the smoking rate among adult Americans was roughly 37% in the early 1970s and is 21% today, a reduction of more than 40%. In contrast, the adult obesity rate increased 135% from 14% in the early 1970s to 32.2% in 2004 National Health and Nutrition Examination Survey [NHANES] 71-04; Figure 1). Because the medical literature has shown that smoking cessation is associated with weight gain, these trends have given rise to a puzzling question: Have efforts to reduce smoking rates in the United States inadvertently caused increases in rates of obesity?
There is substantial evidence that, at least in the short term, smoking and obesity are not independent. Klesges and Shumaker (1992) found that reductions in smoking and/or quitting altogether is associated with increases in dietary intake as well as metabolic changes that promote weight gain. As a result, weight gain is often an unwanted side effect of quitting smoking. The 1990 Surgeon General's Report, The Health Benefits of Smoking Cessation, concluded that the average weight gain after smoking cessation was about 5 pounds or 2.3 kg (U.S. Department of Health and Human Services 1990). However, there is additional evidence that this increase may be short-lived. Mizoue et al. (1998) found that, given enough time, the weight of former smokers inevitably returns to that of never smokers. As a result, the long-term impact on weight of efforts to reduce smoking rates may be negligible.
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To date, three articles have attempted to quantify what proportion of the increase in obesity rates over the past several decades is caused by efforts to reduce smoking. Chou, Grossman, and Saffer (2004) used repeated cross-sections from 1984 to 1999 Behavioral Risk Factor Surveillance System (BRFSS) data to estimate the impact of several state-level measures on body mass index (BMI) and on the probability of being obese, including increases in state-level cigarette prices (Figure 1). The results of this study suggest that increases in cigarette prices may be responsible for as much as 20% of the increase in BMI and trends in obesity rates over this period. This finding is used to argue that rising obesity rates are an unintended consequence of the success of the antismoking movement.
Gruber and Frakes (2006) extended the models presented in Chou, Grossman, and Saffer (2004). Using the same data set, they examined the relationship between cigarette taxes and body weight and argue that cigarette taxes are a more appropriate measure than prices because price changes may be driven by market factors that affect the rates of smoking and eating. Their specification also includes several other differences, including controls for state and year effects. Gruber and Frakes found that cigarette taxes are negatively associated with body weight, suggesting that increases in cigarette taxes result in reductions in BMI. This result is in direct contrast with the findings of Chou, Grossman, and Saffer. However, not even the authors find their result plausible (p. 196).
Flegal (2007) presents yet another analysis of the link between smoking and obesity. Using NHANES data, the author models the contemporaneous relationship between smoking and weight and then reestimates the current prevalence of obesity under the assumption that past smoking levels had remained unchanged. Using this approach, she concludes that decreases in the prevalence of cigarette smoking had only a small effect (less than 1 percentage point) on the overall prevalence of obesity.
In this article, we revisit the analyses presented by Chou, Grossman, and Saffer and Gruber and Frakes to explain the dichotomy of results and provide further evidence of the relationship between antismoking efforts and increases in BMI.
In the conceptual framework of Chou, Grossman, and Saffer, weight is determined by an energy balance equation that relates an individual's calories consumed and expended. Weight does not directly enter an individual's utility function; however, some goods that enter the utility function such as food or cigarettes may also affect the energy balance equation. This provides a reduced-form link between food consumption, cigarette prices, and obesity. To the extent that food and cigarettes are substitute goods, an increase in the price of cigarettes may increase consumption of food (assuming that the income effects are small), increasing equilibrium weight as more calories are consumed. Other effects of an increase in the price of cigarettes are more complex and may also lead to increased weight. Reduced smoking may increase the marginal utility of food (i.e., by improving taste) as well as slow metabolism. The first effect will increase calories consumed in the energy balance equation, while the second effect will lower calories expended; both effects will increase weight.
Chou, Grossman, and Saffer estimate a single obesity equation for all individuals, combining data for never smokers, current smokers, and former smokers. In this reduced-form estimation framework, increases in the price of cigarettes will lower the share of current smokers and increase the share of former smokers. If former smokers have higher weights than current smokers for the reasons outlined above, then the overall effect of an increase in the price of cigarettes will be an increase in weight. The magnitude of the increase will depend on both the change in shares for current smokers and former smokers and the difference in weights between current smokers and former smokers.
In our analysis, in addition to estimating an equation for all individuals, we estimate separate equations for never smokers, current smokers, and former smokers. We expect that increases in cigarette prices will not affect weight for never smokers since they are already operating at a corner solution where they do not smoke. The effect of an increase in the price of cigarettes on current smokers is not clear. Those who continue to smoke but reduce consumption could see an increase in weight for several reasons (e.g., substitute food for fewer cigarettes consumed, more money to spend on food). However, those smokers who do not quit or reduce consumption...
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