Pick Your Poison - Either Way You Lose

Although I started smoking at a very early age, I wasn’t smoking yet when this ad was in the magazines – but it demonstrates the point that the link between smoking and weight has been known since the 1950’s.

Today, it looks like science has finally identified the mechanism:

It's an unfortunate fact that when smokers kick the habit, they often gain weight — a side effect that many smokers use as a reason for not quitting.
Now scientists think they've pinpointed the pathway in the brain through which nicotine helps suppress appetite, suggesting that it's possible to get the same effect without the cigarettes.
Nicotine works on many different receptors in the brain, including those in reward regions that contribute to addiction. But working with mice, a team led by Yale University School of Medicine psychiatrist Marina Picciotto found that the drug also binds to receptors on appetite-regulating neurons, which aren't involved in addiction. These neurons, located in the hypothalamus, send the "I'm full" message after a meal, helping to regulate how much you eat.
It helps explain why smokers aren't as hungry when they smoke, and why they tend to stay thinner on the habit. When they quit, however, many smokers tend to eat more, typically gaining on average about five pounds after quitting.
Picciotto believes that nicotine hijacks various neural circuits in the brain — those involved in reward, and now in appetite — and that understanding how the tobacco compound works on brain cells could lead to better cessation strategies.
Understanding the link between nicotine and satiety, for example, could lead to new drugs that target the nicotine receptors on appetite-controlling cells, giving smokers a way to quit without the weight gain. Already, says Picciotto, there are plant-based quit-smoking drugs available in Eastern Europe that may work in this way, but further research needs to be done to determine whether they'd actually help quitters gain less weight.
"If we had a medicine targeted at these receptors, then people who are not quitting smoking because they are afraid of gaining weight now might make the attempt," Picciotto says. "That's a really exciting area of drug development."
Even if such medicines were to prove effective, however, they may come with side effects. The nicotine receptors that regulate fullness and appetite are also closely linked to the body's fight-or-flight stress response, in which the body revs itself up in the face of a threat. Activating these receptors could lead to increased blood pressure and heart rate, which may not be a good thing for anyone.