Why are one third of American children and adolescents obese or overweight? Recent research
suggests multiple surprising causes such as plate size, a dearth of
home cooking, environmental chemicals, and school schedules that keep
teens from getting enough sleep.
A Scientific American story by Tara Haelle describes three studies that point to environmental factors, rather than genes or inactivity, as spurs to excess weight.
"We're raising our children in a world that is vastly different" from the world of 40 or 50 years ago, Yoni Freedhoff,
an obesity doctor at the University of Ottawa told the magazine. He
says obesity is the consequence of normal kids being raised in abnormal
and unhealthy environments.
Jennifer Orlet Fisher, an associate professor of public health at Temple's Center for Obesity Research and Education,
studied 42 second graders who served themselves in a buffet lunch line.
She found that kids who had an adult dinner sized plate-10.25 inches in
diameter-served themselves 90 calories
more than kids who used a 7.25 inch plate. Kids with the big plates
didn't always eat every bite, but they still ate far more than
classmates with smaller plates. Today's dietary environment offers easy
access to lots of tasty foods in big portions, Fisher says, adding, "To
promote self-regulation you have to constrain the environment to make
the healthy choice the easy choice."
Harvard Medical School Pediatrics Professor David Bickham led a study on the link between obesity and screen time,
studying 921 teens who reported their use of TV, video games and
computers. Bickam and colleagues found games and computer use had no
impact on body mass index (BMI). But TV did. Three common theories say
media fosters obesity because kids are influenced by advertising, they
eat unconsciously, and they are not physically active while they are
sitting in front of a screen. When kids watch TV, researchers found,
their hands are free, and food ads stimulate desire to eat and high
calorie consumption. Viewing healthy fruits and vegetables on the TV
screens may not help. "Our hunger hormones have been honed after
millions of years of dietary insecurity, so when we want to eat, we tend
not to crave green leafy salads," Bickhamsaid. He emphasizes the
relationship between TV and weight is calorie intake, not inactivity.
Another study that deemphasizes the role of inactivity in excess weight involved teenagers and sleep. Jonathan Mitchell, a postdoctoral fellow at the University of Pennsylvania, and colleagues tracked sleep habits of 1,400 teens and found that less sleep
translates into higher a BMI. Lack of sleep had a stronger influence on
the weight of kids who were already obese. Tired, sleep-deprived kids
maybe less active, he noted, but the observed link was not fully
explained by inactivity. Earlier research has suggested sleep
deprivation may disrupt the body's regulatory hormones, which control
hunger and satiety. Freedhoff says "dozens and dozens" of environmental
factors, including more fast food, sugary drinks, the ubiquity of
vending machines and the tendency of adults to use food as pacification
and reward all tend to make kids fatter.
The National Institutes of Environmental Health Sciences has reported that certain chemical exposures may be linked to obesity and diabetes. A study by Dr. Duk-Hee Lee
showed that the risk of diabetes was not increased in overweight people
with low exposures to persistent organic pollutants (POPs), which
suggested to her that exposure to POPs could be an even better
explanation for diabetes than obesity. Several researchers have explored associations between hormone altering environmental chemicals and childhood obesity.
As Freedhoff told the Scientific American,
this problem requires collaboration. It will take efforts by whole
communities including parents, schools, sports teams, and businesses to
"redraft" the environment of children and families.