Overweight people have a tendency to sit, while lean
ones have trouble holding still and spend two hours
more a day on their feet, pacing around and fidgeting,
researchers are reporting in recent findings published.
The difference translates into about 350 calories a
day, enough to produce a weight loss of 30 to 40 pounds
in one year without trips to the gym - if only heavy
people could act more restless, like thin ones.
The difference in activity levels may be biological
and inborn, the researchers say, the result of genetically
determined levels of brain chemicals that govern a person's
tendency to move around. It is the predisposition to
be inactive that leads to obesity, and not the other
way around, they suggest.
The findings, being published today in the journal
Science, are from a study in which researchers at the
Mayo Clinic outfitted 10 lean men and women and 10 slightly
obese ones - all of whom described themselves as "couch
potatoes" - with underwear carrying sensors that measured
their body postures and movements every half second
for 10 days on several occasions. By the end of the
study, which required a staff of 150, the researchers
had collected 25 million pieces of data on each participant.
One thing that convinced the scientists that the activity
levels were innate, and not the product of a person's
being overweight or underweight, was that the levels
did not change when the subjects were forced to gain
or lose weight in different phases of the study. To
make sure they knew exactly how many calories the subjects
were eating, the researchers cooked all their meals
for weeks at a time, and had them pledge not to cheat.
A total of 20,000 meals were prepared.
The director of the study, Dr. James Levine, an endocrinologist
and nutritionist at the Mayo Clinic, said the findings
offered hope to overweight people, suggesting that relatively
simple and painless changes in their daily behavior,
like making an effort to walk more and ride less, could
help control weight. He said increases in obesity in
recent decades could be traced more to declines in daily
exercise - more time spent in cars, behind desks and
in front of computers and televisions - than to increases
In an environment that allows people to be sedentary,
those with a biological predisposition to sit still
will do so, he said. In contrast, the restless ones
will still find ways to burn off calories, even if it
means walking around their desks.
"People with obesity are tremendously efficient," Dr.
Levine said. "Any opportunity not to waste energy, they
take. If you think about it that way, it all makes sense.
As soon as they have an opportunity to sit down and
not waste those calories, they do."
Participants in the study went through three 11-week
phases over a year or so in which their diets were controlled
to maintain, increase or decrease their weight. They
were paid $2,000 at the end of each phase, for a total
Each phase included a 10-day period during which they
had to wear the underwear with the sensors around the
clock, taking it off for only about 15 minutes a day
to shower and get a fresh set from the researchers.
The top was either an undershirt or a sports bra made
of Lycra, and the bottom was a risqué-looking pair
of shorts with openings at the crotch and backside so
the garment would not have to be lowered during the
day, which would have disturbed the sensors.
Dr. Levine said he had designed the outfit with a colleague.
"We had to be very creative," he said. "And you have
to test them for comfort. I would put them on top of
my suit. Mayo has a very strict dress code. Nothing
gave me more pleasure than to wander around with this
bizarre underwear over my suit."
Dr. Eric Ravussin, an obesity researcher at the Pennington
Biomedical Research Center in Baton Rouge, La., who
wrote an essay in Science about Dr. Levine's study,
said that because the tendency to sit still seemed to
be biological, it might not be easy for obese people
to change their ways. "The bad news," Dr. Ravussin said,
"is that you cannot tell people, 'Why don't you sit
less and be a little more fidgety,' because they may
do it for a couple of hours but won't sustain it for
days and weeks and months and years."
But Dr. Rudolph Leibel, an obesity researcher at Columbia
University Medical Center, said, "People can be taught
and motivated to change their behavior in service of
Dr. Leibel also noted that although it was plausible
that the tendency to be inactive was biologically determined,
it had not been proved.