MAYBE WE SHOULDN'T HAVE STOPPED SMOKING
The theory: Obesity rates are up at least partly because smoking rates are down. (Meaning we'd have less of a weight problem if we had more of a smoking problem -- not that anyone thinks that would be a good thing.)
Nonsmokers make up a greater proportion of the population now than they used to. And, on average, nonsmokers weigh more than smokers. It follows that the population as a whole should weigh more than it used to.
The research: Studies show that smokers burn more calories because nicotine speeds up their metabolic rates. It may also curb their enthusiasm for food. This may be why smokers tend to weigh less than nonsmokers and gain weight when they quit.
Smoking rates have gone way down. According to the National Health and Nutrition Examination Surveys for 1971-75 and 1999-2002 -- in which health professionals interviewed and examined thousands of people nationwide -- rates among men ages 25 to 39 fell from 50.4% to 32.3%. Among women that age, rates fell from 39.9% to 28.3%.
But a 2007 study found that the drop in smoking rates couldn't well explain the rise in obesity. The author, Katherine Flegal of the federal Centers for Disease Control and Prevention, projected that if smoking rates hadn't decreased, the obesity rate would have been 22.4% for men ages 25-39 in the 1999-2002 survey, compared with the actual rate of 23.8%. It would have been 30.2% for women in that age group -- again, just a skosh lower than the actual rate of 30.4%.
Yes, Flegal's projected obesity rates were lower than actual rates in all age and gender groups, but never by much -- implying that even if smoking rates had stayed as high as in the past, obesity rates in the latest survey would have been hardly affected.
Our experts weigh in: Assessments of smoking's role in today's obesity rates range from "small" to "not big." Susan Roberts of Tufts University says that, although people gain weight when they quit smoking, often they are gaining back weight they lost when they started. "It does contribute," says James Hill of the University of Colorado, "but it is not a major determinant of the obesity epidemic."
