Smokers need not worry about putting on too much weight after kicking the habit - research has found quitters do not experience greater weight gain than people who have never smoked.
The Otago University research is the latest to draw on data from the Dunedin Multidisciplinary Health and Development Study, which had closely tracked the progress of about 1000 people born in Dunedin in 1972-73.
Researchers measured the group's smoking habits and weights at regular intervals between the ages of 15 to 38. About a third were smokers at age 21, and of those, about 40 per cent had quit by age 38.
The study concluded that, on average, quitters did not experience greater weight gain than those who never smoked.
Over the 17 years of the study, the quitters' weight returned to the same level as people of similar age who had never smoked in the first place.
Furthermore, those who quit smoking gained only a relatively small amount of weight - around 5kg - compared with people who carried on smoking. The findings were the same for both men and women.
The researchers also found being a smoker did not prevent long-term weight gain. All groups in the Dunedin Study tended to put on weight over time, regardless of their smoking status.
Lead researcher Lindsay Robertson, an assistant research fellow at the university's Cancer Society Social and Behavioural Research Unit, said some earlier research had suggested people might gain large amounts of weight after quitting, but many of these studies were not very reliable.
"We hope that our findings will encourage people who are thinking about quitting. They should not be put off by the fear of putting on large amounts of weight. It is important to be aware that a small weight gain is unlikely to offset the health benefits of quitting.''
The study has been published online in the journal Nicotine and Tobacco Research.