Speaking of which, nicotine is another effective weight loss drug. I have to wonder if some portion of the increase in median BMI (ignoring the morbidly obese) in America over the last 50 years is it becoming less socially acceptable to chain smoke.

Looks like it's typical to gain 5-10lbs when quitting smoking.

Edit: pulled up the data and there's been a 30lb increase in median weight in America, so (loosely guessing) the smoking effect is probably somewhere between 5 and 10% of that change.