Quitting smoking leads to an average weight gain of four to five kilogrammes (nine to 11 pounds) in the first year -- "significantly" more than previously thought, a study said Wednesday.
Most of the pounds are piled on in the first three months, a team of medical researchers wrote in the online journal bmj.com, as another group stressed that the health benefits of quitting far outweighed the risks of putting on weight.
For quitters who did not use nicotine replacement therapy, the average weight gain was 1.1 kilos at one month, 2.3 kilos at two, 2.9 kilos at three, 4.2 kilos at six months and 4.7 kilos after a year.
This was "substantially higher than the 2.9 kg often quoted in smoking cessation advice leaflets," wrote the team from universities and medical research facilities in France and Britain.
"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."
Earlier research showed that nicotine is an appetite suppressant and may increase the metabolic rate.
For the latest paper, the researchers collated data from earlier studies conducted between 1989 and 2011 in the United States, Europe, Australia and east Asia to assess weight changes among successful quitters.
The researchers stressed that changes in body weight varied greatly, with about 16 percent of quitters losing weight and 13 percent gaining more than 10 kilos in the first year.
In an editorial accompanying the paper, experts from Spain and Australia said modest weight gain was far less life-threatening than smoking.
"Tobacco is the main cause of premature death worldwide, being responsible for 5.1 million deaths each year. Obesity, together with overweight, causes 2.8 million deaths," they wrote.
"Cohort studies indicate that modest weight gain does not increase the risk of death; smoking does."
They stressed that fears of getting fat could deter some people from quitting and called for further research to identify those most at risk of gaining weight to be targeted for counselling.