Fwiw, I lost about 4 kg of my average weight (That was about 7% of my body weight) when I stopped smoking. A couple of years down the road I also quit drinking which also decreased my average weight by another 4 kg.
(With average weight I take into consideration that I have natural, not dieting related fluctuations of about +/- 1 to 2 kg. The fluctuations are still there but the mean they deviate from is vastly different.)
Maybe I should add that I am still eating about five pounds of sugar a day and I haven’t done sports since 2012, so don’t assume that quitting smoking meant a healthier lifestyle (sadly).