Kicking the smoking habit can often lead to an unwelcome side effect: an increase in waist circumference. However, a recent study suggests that physical activity plays a crucial role in mitigating this weight gain. Conducted by researchers and published in the International Journal of Obesity, the study examines how smoking status and leisure-time physical activity (LTPA) influence changes in waist circumference over a decade, taking into account genetic and environmental factors.
The study, titled “Associations of Smoking Status and Leisure-Time Physical Activity with Waist Circumference Change—10-Year Follow-Up Among Twin Adults,” draws on data from the FinnTwin16 cohort. This research involved Finnish twins initially surveyed between 2000 and 2003, with a follow-up a decade later. The study provides valuable insights into how lifestyle choices post-smoking cessation affect long-term health outcomes.
The Health Trade-Off: Smoking Cessation and Weight Gain
Can quitting smoking trade one health risk for another? Globally, over a billion adults smoke, and a significant portion intends to quit despite concerns about weight gain. Nicotine is known to suppress appetite and increase metabolic rate, but its withdrawal can reverse these effects, leading to increased visceral fat. While waist circumference (WC) has surpassed body mass index (BMI) as a better predictor of cardiometabolic risk, the role of regular LTPA in counteracting central adiposity post-cessation remains underexplored.
The study’s findings underscore the importance of physical activity in managing weight after quitting smoking. Regular LTPA has been shown to counteract overall weight gain, yet its impact on long-term central adiposity after quitting smoking was previously unclear. The research aims to fill this gap by examining the causal links blurred by family genetics and upbringing.
Study Methodology and Findings
The analysis included 3,322 individuals (46% men) from the FinnTwin16 cohort, excluding those with pregnancies or missing data. Participants provided information on smoking behavior, LTPA, WC, and other covariates. Smoking status was categorized into persistent smokers, quitters, and non-current smokers, with a separate “others” group excluded from primary interpretations due to diverse smoking patterns.
LTPA was quantified using metabolic equivalent task-hours per week (MET-h/week), including active commuting. WC was self-measured with standardized instructions and modeled as the follow-up value adjusted for baseline WC. Linear regression, clustered by family, estimated associations between smoking or LTPA and WC change, adjusting for confounders. Fixed-effects models compared dizygotic (DZ) and monozygotic (MZ) twin pairs discordant for exposure.
At baseline, non-current smokers gained 6.1 cm, persistent smokers 6.6 cm, and quitters 8.4 cm in waist circumference over ten years. Quitting daily smoking predicted an additional 2.0 cm WC increase compared with continuing smokers.
The study found that while quitting smoking was associated with increased WC, physical activity had a protective effect. Each extra MET-h/week at baseline corresponded to 0.05 cm less WC growth, and every unit increase in LTPA during follow-up reduced gain by 0.06 cm, independent of smoking group. Quitters increased their LTPA on average, suggesting that physical activity helped cushion their metabolic load.
Genetic Insights and Implications
Twin analyses provided further insights into the role of genetics and environment. Among DZ pairs discordant for smoking cessation, the quitting twin showed 2.6 cm more WC growth than the smoking co-twin. However, this difference disappeared in MZ pairs, suggesting familial factors may moderate weight rebound after quitting.
The authors caution that the small sample size of identical twins in this part of the analysis limits the strength of these conclusions. Sensitivity tests showed no interaction between sex and smoking or between LTPA and smoking on WC change, allowing for the pooling of data from men and women.
“The cardiovascular advantages of quitting smoking are accompanied by a measurable expansion of central adiposity,” the study concludes. “Yet, higher LTPA reliably tempered waist growth across all genetic strata.”
Future Directions and Recommendations
The study highlights the need for integrated cessation programs that include exercise guidance to protect metabolic health without undermining quit success. Policymakers and clinicians are encouraged to prioritize such interventions. The authors also call for future research with larger twin samples and objective measures of activity and smoking to confirm these findings.
Ultimately, the study suggests that while quitting smoking may lead to short-term weight gain, maintaining an active lifestyle can help mitigate these effects. This research underscores the importance of addressing lifestyle factors in smoking cessation programs to ensure long-term health benefits.
