Our meta-analysis has shown that abstinent smokers gain a mean weight of 4-5 kg after 12 months of abstinence. However, we have found substantial variation in weight gain, indicating that this mean value does not reflect many people who give up smoking. We estimated that at 12 months, 16-21% of participants lost weight and 13-14% gained more than 10 kg.
Although weight gain after smoking cessation is widely recognised, this meta-analysis provides clinicians and patients with a more robust and detailed description of the first 12 months of weight change after cessation. The finding of a mean weight gain of 4.7 kg in untreated quitters at one year after smoking cessation is substantially higher than the 2.9 kg often quoted in smoking cessation advice leaflets, which stemmed from a previous review.1
Moreover, this mean weight gain is greater than the 2.3 kg gain that female smokers report being willing to tolerate, on average, before embarking on a quit attempt.48
This review reports on variation in weight gain, which is rarely described or discussed in the literature, and has clinical implications. Some people are either destined or able to prevent weight gain without intervention, whereas others seem likely to gain enough weight that puts them at increased risk of diabetes, among other complications.49
In practice, doctors could detect people gaining excessive weight and intervene early to prevent this.
We were unable to show a significant difference between weight change estimates in point prevalence abstainers and prolonged or continuous abstainers, and therefore, we combined all estimates at each time point regardless of abstinence definition. This may be because the data were derived from clinical trials, in which participants were all given the same target quit date, and therefore many point prevalence abstainers were also prolonged abstainers.50
However, the point estimate did indicate a smaller weight change in point prevalence abstainers and it is possible that this difference was the case in our analysis, although it was not sufficiently powered to detect statistical significance.
Most trials aimed at preventing weight gain typically enrolled weight concerned women, but did not provide clear evidence that this group were at risk of greater weight gain. This result might seem surprising, since people concerned about weight may have experienced excessive weight gain in previous quit attempts, and excessive gain is associated with greater weight gain in a current quit attempt.51
However, the association between weight concerns and weight gain after cessation is unclear.18
Furthermore, nearly all such trials recruited exclusively women, whereas trials appealing to the general population were all mixed sex. Consequently, the data were inevitably confounded and also not precise enough to exclude a difference between weight concerned populations and populations not specifically concerned about weight gain.
Our estimates provided the difference between starting weight and weight up to one year later. The mean weight of a population is likely to increase over one year independently of a smoking cessation attempt.54
The Lung Health Study showed that continuing smokers gain on average of 0.3 kg/year for men and 0.5 kg/year for women.55
estimated a gain of about 0.3 kg/year for both sexes, meaning that roughly 4.3 kg of the mean weight gain at 12 months in our analysis was due to cessation (table 3).
These data relate only to weight gain in people who achieve and maintain abstinence, but provide no evidence on what happens to weight in smokers who are abstinent and then relapse or in continuing smokers who never achieve abstinence. For smokers who gain weight on cessation, available data suggest that they lose weight again if they relapse to smoking,56
although few studies have reported data for weight gain in those who relapse. An incremental weight gain would be important because many people repeatedly attempt to quit. Furthermore, because few trials followed participants beyond one year, we cannot report here on weight gain beyond this time point. Evidence is conflicting as to whether weight continues to increase beyond the first year after cessation.55
We limited our review to randomised controlled trials for smoking cessation, pharmacotherapy use, exercise, and interventions aiming to prevent weight gain. The validity of data for weight gain after cessation depends on accurate timing of the start of abstinence, the validity of recording of abstinence, and frequent follow-up. Most of the trials we reviewed show these features but few observational studies do. We also limited our review to trials in the Cochrane reviews of first line treatment, which led to the exclusion of a few other trials, chiefly the Lung Health Study.55
However, estimates of the effect of cessation on weight gain at one year from the Lung Health Study were similar to our estimates, and there was no reason to presume that using data from only randomised controlled trials created a bias.
These data were derived from smokers treated in clinics for tobacco dependence. Such groups are usually more dependent and heavier smokers than the general population of smokers. There is conflicting evidence that heaviness of smoking relates to weight gain,4
with different studies reporting that heavier smokers gain more weight, or that moderate smokers gain most weight. Smokers seeking treatment could differ from those who quit on their own in other ways. Most people do not attend smoking cessation clinics or consult their doctor for help until they have tried and failed to stop smoking themselves. Their previous failure to accomplish one goal, smoking cessation, could reflect on their ability to limit weight gain after cessation. This theory is speculative, however. The differences between the population enrolled in clinical treatment and smokers quitting without clinical help could be related to weight gain after cessation. A systematic review of population based studies, taking careful account of the assessment of continuing abstinence, would be needed to assess weight gain after smoking cessation in the general population. Therefore, our review data are directly relevant to clinicians who only treat smokers who present for help with cessation.
Weight gain was reported in only 25% of the smoking cessation trials considered for inclusion. It was not possible to determine whether those studies reporting weight were a biased sample of all smoking cessation trials, although we found no evidence of bias on the funnel plot. Trials that aimed to prevent weight gain after cessation reported weight change as a primary outcome, and we observed no difference in weight gain between these trials and the treatment trials, in which only a minority reported weight gain.
Different studies, and therefore different study participants, contributed data to the meta-analyses at each time point and we noted heterogeneity in most analyses. We therefore cannot interpret mean weight change across different time points as a trajectory. Studies would need to report individual weight gain trajectories, rather than cross sectional means, for us to summarise these changes. Large weight gain might lead to intentional relapse to smoking, which would mean that people who put on large amounts of weight early in their quit attempt and relapse were not represented by our data. However, data are conflicting for the association between weight gain and probability of relapse.51
Previous reports have underestimated the average amount of weight gained when people stop smoking. In clinic treated smokers, the population mean is about 4-5 kg after 1 year. Weight gain is greatest during the first three months of quitting (average monthly weight gain of about 1 kg), after which the rate of increase declines. However, we saw a large variation around the population mean. At 12 months, about 16-21% of participants lost weight and 13-14% gained more than 10 kg.
Weight gain is important because weight concern is widespread among smokers and could deter some from trying to quit. Gaining weight after cessation limits some of the health benefits of quitting and is associated with an increased risk of health problems.69
So far, interventions have had a limited effect on preventing weight gain.12
These data suggest that doctors might usefully give patients a range of expected weight gain, although further research should identify the subgroups most at risk of gaining weight and clarify the optimum content and timing of interventions to prevent weight gain after cessation.
What is already known on this topic
- Smoking cessation is often followed by an increase in bodyweight, but estimates vary and are not well grounded
What this study adds
- Smoking cessation is associated with a mean increase in body weight of about 4-5 kg after 1 year, with most weight gain occurring within three months of quitting
- Changes in body weight vary widely, with around 16% of quitters losing weight and 13% gaining more than 10 kg