Quitting Smoking Can Increase Weight More Than We Thought

Obesity is a growing health problem in the United States with prevalence rates rising from 13 percent in the 1960s to 35 percent in 2012. The United States has the highest obesity rate in the OECD, but the world is keeping pace: The World Health Organization has declared obesity to be an epidemic, as it has become increasingly widespread even in poor countries. Obesity-related diseases lead to about 112,000 deaths per year in the United States with associated medical expenses totaling $190 billion per year, making this matter  worthy of concentrated policy efforts and research.

Since the 1960s, tobacco use has been declining from 42 percent to 19 percent of the U.S. adult population. This is good news, given the rich evidence that smoking leads to diseases including lung cancer, heart disease, and stroke—making it responsible for one in five deaths in the U.S. and at least $130 billion per year in medical expenses.

While tobacco cessation has positive health benefits overall, one side effect is increased obesity rates. Previous research has shown that reducing smoking can increase body weight due to nicotine’s ability to act as an appetite suppressant and metabolic stimulant. A recent study using a randomized control trial provides a more reliable estimate of the relationship between smoking cessation and weight gain, claiming the size of the impact is greater than previous estimates.

In their study, Chourtemanche and colleagues use micro data from the Lung Health Study, which randomly assigned smokers to a comprehensive smoking cessation program and tracked their health over five years. They found quitting smoking lead to an average short-run weight gain of 1.5 to 1.7 Body Mass Index (BMI) units, which translates to around 10 to 11 pounds at the average height. The researchers were able to isolate the effect of smoking cessation on weight gain from others factors, like the tendency for individuals to gain weight with age and the level of interest in one’s health. Overall, these  factors induced negative biases in previous associational studies, potentially explaining the lower estimates compared to those of Chourtemanche and colleagues.

Chourtemanche and colleagues’ paper also shows that the causal effect they found persists  five years after quitting, contradicting previous findings that weight gain diminishes with time for this population. These long-run estimates imply that the decline in smoking explains around 14 percent of the rise in BMI in recent decades. Additionally, their subsample analysis demonstrates that on average younger individuals, females, individuals without college degrees, and those with the lowest baseline BMI levels gain the most weight in response to smoking cessation.

It is worth clarifying that the spirit of Chourtemanche and colleagues’ work is not attempting to discourage smoking cessation out of fear of weight gain. The epidemiological evidence shows any increase in body weight after quitting smoking is more than compensated for by health improvements. The results of this randomized controlled trial should serve as a call for further investigation into medical and policy interventions that can help prevent quitters from gaining weight. If programs could reduce this side effect of smoking cessation, tobacco control efforts could become even more effective in terms of overall health gains.

Article source: Courtemanche, Charles, Rusty Tchernis, and Benjamin Ukert. “The Effect of Smoking on Obesity: Evidence from a Randomized Trial.” NBER Working Paper No. 21937 (2016).

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