Evidence for the expanding epidemic of childhood obesity is thinning.
Nutritionists, health advocates and media reports have been sounding the alarm about a rise in childhood obesity, which could lead to diabetes, heart disease and other problems. But a series of studies from half a dozen countries suggest that rates have held steady over the past five to 10 years, albeit at levels much higher than in the 1960s and 1970s.
The reasons behind the leveling off in childhood obesity in the U.S., Australia, France, Switzerland, Sweden and New Zealand remain shrouded in mystery.
Map: Compare childhood obesity rates, state by state, in 2003 and 2007.
Obesity rates could have hit a plateau, some scientists propose, if only a certain percentage of children are genetically predisposed to obesity, and that share has gotten fat already. Timothy Olds, a professor of health sciences at the University of South Australia, believes genetics could play a role, but he also points to "all the little things people are doing to encourage healthy weight."
Some researchers argue the data used to produce these conclusions are flawed. And other scientists say that while the methodology of the recent batch of studies appears sound, the findings aren't definitive. Future surveys using different methodologies, they say, could show obesity rates on the move again.
"Most developed countries are not doing annual surveys," says Tim Lobstein, director of policy and programs for the International Obesity Taskforce, a London-based research and advocacy group. "We probably know more about growth patterns in cattle than we do for human children."
In the U.S., obesity rates among children hovered at about 16% between 2002 and 2006, according to the U.S. Centers for Disease Control and Prevention. The leveling off was a surprise to William Dietz, director of the CDC's division of nutrition, physical activity and obesity, who notes that prominent anti-obesity-awareness campaigns have only been around for a few years. (A survey conducted by the National Opinion Research Center, a group based at the University of Chicago, showed increases in most states between 2003 and 2007, but that was based on phone interviews rather than physical examinations.)
Similar trends have shown up in Australia, where childhood obesity has held at 5% to 6% for about a decade. Prof. Olds led the research at the University of South Australia that found the stable level of childhood obesity in that country. But his findings are disputed by another group of Australian researchers, working with the Obesity Taskforce in London. According to their own analysis announced earlier this month, there has been a continued increase in the number of Australian children who are overweight or obese. The two camps disagree over which surveys should be included in the study, and over whether to consider the overweight and the obese separately, or together.
Where scientists tend to agree, though, is that even countries with relatively high levels of health-care spending don't do enough to monitor children's weight, making it difficult to pinpoint turnarounds.
The Numbers Guy Blog
Maybe Children Aren't Getting Fatter
Dr. Lobstein pines for the days when students expected to be lined up by the school nurse for height and weight measurements. Instead, researchers today struggle to find samples suitably large and representative. Few countries assess students on an annual basis, as some scientists advocate, and there is a considerable lag in crunching the numbers and identifying trends. The CDC has measured children and adults by height and weight since 1999, compiling enough numbers for a statistically robust report every two years. Other countries' surveys are more haphazard. And outside the developed world, data can be scarce, and more time elapses between surveys.
Even when a child's height and weight have been measured, it isn't clear how to determine who is overweight and who is obese. Body mass index -- weight in kilograms divided by the square of height in meters -- is notoriously unreliable for diagnosing individual adults with obesity, ensnaring brawny body builders along with the genuinely corpulent.
BMI is an even worse barometer for children, whose growth patterns change over time. So rather than rely on absolute BMI numbers to define obesity, as is done for adults, researchers generally label children as overweight when their BMI exceeds the 85th percentile, and obese if their BMI tops the 95th percentile.
These percentiles are defined using height and weight data from decades ago, before obesity rates surged and children were at healthier weights. That approach helps avoid overlooking some plump children, but it introduces some uncertainty about exactly how far back to go when comparing today's youth with yesterday's.
And the numbers researchers have amassed on obesity don't offer a precise picture of which children might be at risk of health problems due to weight. For some conditions, excess weight below the "overweight" level can be dangerous. Meanwhile, some studies have shown that slightly overweight people -- which could include those muscle-bound BMI false positives -- live longer than their thinner counterparts.
Statisticians noted these limitations when asked to review the various studies showing no signs of an increase in children. Susan Paddock, a senior statistician at RAND Corp., a think tank, found the methodologies to be "generally sound," but added, "these papers do not prove that obesity/overweight rates have leveled off, but rather that a significant trend was not found." It is possible that obesity rates were increasing slightly -- or even declining slightly -- but that these changes were too subtle to be detected by the infrequent, comparatively small surveys.
Still, this represents a change from the 1990s, when rapid increases in childhood obesity in developed countries were statistically significant. "Hopefully we have come to some kind of an end to this story," says Max Petzold, associate professor in epidemiology at the Nordic School of Public Health in Goteborg, Sweden. "It's not stopping at a good level. But the problem seems to be a little more under control."
Nonetheless, the global spread of obesity, and increases in adult rates even where childhood rates have leveled off, have helped make the notion of an unabated epidemic the prevailing storyline.
"When the data of rather high obesity rates were first published in 2004, everyone was talking about it and we had calls...at the lab," says Isabelle Aeberli, who studies obesity in Switzerland at Zurich's Swiss Federal Institute of Technology. But when new data were made public showing a decrease in obesity, there was little reaction outside the scientific community. "It just seems to be more interesting to the general public to show something bad as compared to something good," Ms. Aeberli adds.
Some health advocates have been leery of giving too much attention to the encouraging numbers, noting that a plateau or small decrease won't stave off the high financial and medical toll likely in store for today's overweight children.
"What I worry about is that people will read these numbers and think we've got this solved," says Dr. Dietz of the CDC. "I'm encouraged by the results, but this is no time for complacency."
Write to Carl Bialik at numbersguy@wsj.com
Article Source: online.wsj.com/article/SB124821547930269995.html
RSS 2.0