What Makes Smokers So Skinny?
Animal studies give researchers new clues about why smokers gain weight when they quit.
If there’s one thing every smoker knows, it’s that cigarettes are terrific appetite suppressants. It doesn’t seem fair, but on average, smokers weigh less than non-smokers. Young women certainly know it. Consider the familiar image of smoking ballerinas and models--women performing in businesses where gaining two pounds can mean the loss of a job. Gymnasts, ice skaters, and other athletes have also looked to cigarettes for help with weight control. The average weight gain for women, writes researcher Cynthia Pomerleau, in her book, Life After Cigarettes, is ten pounds, with a quarter of female quitters gaining five pounds or less, and about a quarter gaining more than 15 pounds.
Is there a way to gain the benefits of this weight-loss effect, without all the lethal baggage of actually smoking? Big Pharma has been trying to bring a safe and reliable weight loss pill to market for years, and has only a string of spectacular failures to show for it—Fen-phen being one of the latest. But behavioral neuroscientist Marina Picciotto and coworkers have discovered an entirely new pathway through which nicotine influences eating. They used a mouse model to show that activating one particular subset of nicotine receptors caused the mice to eat less. What astonished the researchers was the strength of this special nicotine receptor, and its overwhelming effect on the weight of the test mice: “Their body fat dropped 15% to 20% over 30 days,” according to a commentary in Science.
Here’s what happens: Nicotine activates a chain of neuronal events that ends up releasing a hormone called melanocortin in the brain. And melanocortin inhibits feeding behavior. This was a surprise—scientists had assumed that appetite suppression was another result of nicotine’s effect on dopamine reward systems. But the new study suggests that appetite, as Sarah Williams wrote in Science, “has its own pathway.” One potentially huge hole in the study: It dealt with only male mice. Since women experience more weight fluctuation than men, Picciotto said she plans further experiments with female mice.
What does it mean? NIDA director Dr. Nora Volkow remarked that the results “indicate that medications that specifically target this pathway could alleviate nicotine withdrawal as well as reduce the risk of overeating during smoking cessation.” Picciotto thinks it may lead to a new treatment that accomplishes two things: By isolating and stimulating one particular kind of nicotine receptor, it may be possible to suppress appetite when smokers stop smoking. And a drug that stimulates only the targeted subset of nicotine receptors might lead to a safe and effective weight loss drug—the Holy Grail of the weight loss community.