Staying active reduces waist gain after you quit smoking

By Dr. Priyom Bose, Ph.D.Reviewed by Lauren HardakerJul 1 2025

A decade-long twin study reveals that an active lifestyle could be the key to managing the growing waistline often seen in people who quit smoking.

Study: Associations of smoking status and leisure-time physical activity with waist circumference change—10-year follow-up among twin adults. Image credit: Krzysztof Winnik/Shutterstock.com

A recent International Journal of Obesity study explored the associations of leisure-time physical activity (LTPA) and smoking status with weight circumference (WC) change.

Weight gain, smoking habits, and leisure-time physical activity

Existing evidence indicates that individuals typically gain about three to six kilograms of body weight on average in the first year after quitting smoking, depending on factors like age and sex. This weight gain could potentially counteract some of the health benefits associated with quitting smoking. WC might be a more informative health-related measure than overall weight, as it predicts weight-related health conditions better. Currently, there is limited evidence on the long-term changes in abdominal obesity following smoking cessation.

The evidence is inconsistent regarding the effectiveness of LTPA in influencing weight gain after quitting smoking. Our understanding of the impact of LTPA on changes in abdominal obesity post-cessation is also limited. Familial influences like shared genetic and environmental factors may confound these associations. Therefore, twin samples are particularly useful in epidemiological research to examine familial factors' influence and test whether observed associations are causal rather than due to shared genetics or environment.

About the study

The current study utilizes 10-year follow-up data from Finnish twins to explore the association between smoking cessation and changes in WC and whether higher levels of LTPA are linked to smaller increases in WC. Additionally, the study examines the role of familial influences in these associations. Two surveys were conducted during 2000 - 2003 (baseline) and 2010 - 2012 (follow-up), with 5,240 and 4,397 individuals completing them, respectively.

Abdominal obesity was assessed using self-measured WC in centimetres at baseline and follow-up. Four categories were devised for smoking status: persistent smokers, quitters, non-current smokers, and others. The quitters were daily smokers at baseline but quit during the follow-up. In contrast, the “others” group comprised individuals with miscellaneous smoking status, such as relapses, initiators in follow-up, and so on. Due to the heterogeneity of the “others” group, no interpretations were made for this category in the primary analyses.

LTPA was calculated using the self-reported duration (minutes per session), frequency (per month), and average intensity in metabolic equivalents (METs). Allowances were also made for daily commuting to and from work. These measures were used to calculate the total MET index of LTPA hours per week. One MET is defined as the energy cost of sitting quietly.

Several confounders were accounted for, including body mass index (BMI), sex, age, baseline socioeconomic status, sleep problems, diet quality, alcohol use, psychological distress, and life satisfaction.

Study findings

The current study included 3,322 participants, of whom 55.9% were non-current smokers. The study cohort also comprised 8.2% of quitters from baseline daily smoking, 19.3% involved persistent or occasional smoking, and 16.6% were categorized as others. During the follow-up, approximately 36% of baseline daily smokers had quit smoking.

During the 10-year follow-up, the mean increase in WC was 6.5 cm. This increase varied from 6.1 cm among non-current smokers to 8.4 cm among those who quit daily smoking during the follow-up. In comparison to participants who continued smoking, the WC increase was statistically significant only among those who quit daily smoking. The adjusted difference was approximately 2.0 cm greater for quitters than persistent smokers, although familial factors may influence this association.

During the follow-up period, levels of LTPA declined across all smoking status groups, except among individuals who had quit daily smoking. Among this group of quitters, LTPA increased by an average of 5.0 MET-h/week. Regardless of smoking status, each additional MET-h/week was associated with a smaller increase in WC. However, the effect size was modest, about 0.06 cm less WC gain per additional MET-h/week, meaning a person would need to increase activity by approximately 20 MET-h/week to reduce WC by 1.0 cm.

A total of 34 dizygotic (DZ) pairs and 11 monozygotic (MZ) smoking-disconcordant twin pairs were included in this sub-analysis. Among MZ pairs, those who quit smoking were not associated with a WC increase. This finding implies that the co-twin who had quit smoking did not undergo increased WC when compared to their co-twin who continued daily smoking. In the case of DZ pairs, the co-twin who stopped smoking had a larger WC increase. This suggests that shared genetic or familial environmental factors may confound the observed association between smoking cessation and WC gain in the full sample.

Within-pair analyses revealed that each additional MET-h/week of LTPA decreases the risk for WC increase. This association remained significant for both DZ pairs and MZ pairs. A similar effect size was observed in all individuals and the within-pairs analysis. Ambiguous estimates generated in the within-pair analysis could be attributed to shared familial confounding and/or the small sample size of smoking-discordant twin pairs, which limited statistical power. Importantly, the consistency of LTPA’s protective effect across individual and twin-pair models strengthens the case for a potential causal relationship.

Conclusions

A 10-year follow-up study highlighted several trends among the adult twins, including a decrease in smoking prevalence, reduced LTPA, and elevated abdominal obesity.

Among twins, smoking cessation was linked with a moderate increase in WC. However, this association weakened or disappeared when shared familial factors were controlled for, suggesting it may not be causal.

LTPA appeared to protect against post-cessation WC increases independent of familial influences. The effect was small but consistent across individual-level and twin-pair analyses, supporting a possible causal effect.

The current study highlights the importance of incorporating regular physical activity into lifestyle interventions to mitigate the risk of post-cessation abdominal obesity.  It also highlights the need for post-cessation weight management programs that consider behaviour and genetic factors.

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