In Brief: Study suggests how nicotine suppresses appetite
On average, smokers are thinner than nonsmokers but tend to gain weight once they kick the habit. The fear of weight gain stands as one of the obstacles to quitting.
But it's never been clear why smokers gain weight once they stop smoking. One line of research suggests that nicotine — the addictive chemical in cigarettes — also acts as an appetite suppressant. Presumably, then, some people add pounds after they quit smoking because they get hungry and eat more.