John: Hello, I'm John Hilton, senior editor at Cochrane. There are many Cochrane Reviews of ways to help smokers to quit. One of these, on research into interventions that might help in reducing any subsequent weight gain was updated in October 2021. Annika Theodoulou from the University of Oxford in the UK worked on the update and tells us what they found in this podcast.

Annika: Quitting is one of the best things that smokers can do to improve their health, but many people who stop smoking gain weight. This can discourage some people from making a quit attempt and risks offsetting some, but not all, of the health advantages of quitting smoking so it's important to identify effect ways to prevent this weight gain.
When this review was last updated in 2012, the authors found insufficient evidence to recommend any one type of intervention targeting post-cessation weight gain. Since then, considerably more research has become available and new smoking cessation treatments have come to market, prompting the need for this update, which involved searching the literature up to October 2020.
This review is broken down into two parts. In part 1, we review the effects of interventions, such as dieting, that specifically aim to limit post-cessation weight gain. We were interested in weight change at any follow-up timepoint, smoking cessation at 6 months or more after quit day and whether there were adverse events following any pharmacotherapy interventions. In part 2, we review the effects of interventions designed to aid smoking cessation that might also affect post-cessation weight gain, such as antidepressant medication, at any follow-up timepoint. 
For part 1, we have added 21 studies and now include 37 studies on specific programmes for weight control, reporting on more than 11,500 people trying to stop smoking, and although some behavioural interventions suggested benefit, certainty in the evidence was limited across all comparisons. We also found that although a range of pharmacological interventions were tested, most of the trials only followed up participants in the short term, primarily at the end of treatment and none showed evidence that weight gain was prevented beyond six months.
In part 2, we added 27 studies, bringing us to 83 completed randomised trials reporting on more than 46,000 people. In total, we examined evidence for six different interventions that are used to support smoking cessation and which might incidentally reduce weight gain. But, overall, we found no intervention for which there is moderate certainty of a clinically useful effect on long-term weight gain. There is also no moderate- or high-certainty evidence that interventions designed to limit weight gain reduce the chances of people achieving abstinence from smoking.
In conclusion, we'd like to see more studies of the interventions we've included in the review to date, of new interventions that might help and of ways to alleviate smokers' concerns about putting on weight if they quit smoking. These studies should also include longer follow-up, ideally beyond six months.

John: If you'd like to find out more about the interventions included in the review and the certainty of the evidence for these, the review, and future updates of it, can be found online. Just go to Cochrane Library dot com and search 'preventing weight gain after quitting smoking'.