The latest data from the National Health and Nutrition Examination Survey, reported in this week's Journal of the American Medical Association, confirm that obesity rates among American children and adults have leveled off in recent years. Since 1999 the prevalence of high body mass index among children and adolescents has remained essentially the same. Among women in the survey, the rate of obesity (defined as having a BMI of 30 or more) was about 33 percent in 1999–2000, 2001–02, and 2003–04, then 35 percent in 2005–06 and 2007–08. Among men, the rate rose from 31 percent in 2003—04 to 33 percent in 2005–06 before declining to 32 percent in 2007–08. Reporting the data in JAMA, researchers at the CDC's National Center for Health Statistics conclude that "the increases in the prevalence of obesity previously observed do not appear to be continuing at the same rate over the past 10 years, particularly for women and possibly for men."
William H. Dietz, director of the CDC's Division of Nutrition, Physical Activity, and Obesity, is sounding more optimistic than he did when discussing BMI trends last summer. "Right now we've halted the progress of the obesity epidemic," he tells The New York Times. "The data are really promising." That may sound like Dietz is taking credit for stopping our transformation from man to manatee, but he thanks Mom (and possibly less apple pie):
Dr. Dietz said the data probably reflected increased awareness of the obesity problem, especially among women, "who buy food, prepare it and see it, and they're making changes for themselves that they're also making for their kids." He also cited a reduction in "less healthful foods" at school.
David Ludwig, director of the Optimal Weight for Life Program at Children's Hospital Boston, is less confident that lifestyle changes account for the plateau:
Dr. Ludwig said the plateau might just suggest that "we've reached a biological limit" to how obese people could get. When people eat more, he said, at first they gain weight; then a growing share of the calories go "into maintaining and moving around that excess tissue," he continued, so that "a population doesn't keep getting heavier and heavier indefinitely."
Furthermore, Dr. Ludwig said, "it could be that most of the people who are genetically susceptible, or susceptible for psychological or behavioral reasons, have already become obese."
In other words, WALL-E was not a documentary. But that does not mean we should succumb to complacency, which would threaten public health, the CDC's budget, and obesity research grants:
Experts like Steven Gortmaker, a Harvard public health professor, said obesity would decline only with new policies, like penalties and incentives to promote healthier foods and exercise.
"If you look at the reversal of the smoking epidemic," Dr. Gortmaker said, "substantial change didn't really happen until there were bans on advertising and limits on consumption through things like taxation. We have to make some substantial changes."
I'm not sure what sort of "penalties and incentives" Gortmaker has in mind to get us to eat our vegetables, turn off the TV, and go for a jog. But it's not true that the decline in smoking occurred after tobacco advertising was banned and hefty taxes were levied on cigarettes. Per capita cigarette consumption began to fall after the January 1964 surgeon general's report linking smoking to lung cancer. It rose a bit in 1965 and 1966, dropped for four consecutive years, and rebounded slightly in the early 1970s. But it never returned to its 1963 peak, and in 1974 it began a steady decline that continued for two decades. The ban on TV and radio commercial for cigarettes took effect in 1971 and was actually followed by an increase in cigarette consumption. Other substantial restrictions on advertising (such as the billboard ban included in the 1998 Master Settlement Agreement) were not imposed until relatively recently, and the same is true of big tax hikes aimed at discouraging consumption. Leaving aside the morality of paternalism, the experience with smoking does not suggest that coercive measures are necessary to move people toward healthier lifestyles.
The JAMA article on BMI trends in adults is here; the one about BMI trends in children and adolescents is here. My earlier discussion of the weight plateau is here and here. My critique of the War on Fat is here.