Skipping Exercise Makes Fat a Bigger Problem
Exercise benefit may depend on daily activity
April 19, 2005 -- After a tough workout, you deserve a rest. But don't let
that rest last too long.
Soon after exercise, fat cells start storing up energy. If you don't
exercise again -- soon -- those fat cells will swell in size and weight, report
University of Missouri-Columbia researchers David S. Kump and Frank W. Booth,
Why? Kump and Booth point to human evolution. Because food was often scarce,
our bodies grew very efficient at storing away any food energy not burned off
"Left on its own in nature, our body wants to store as much energy (fat)
as possible because it doesn't know when the next meal will come," Booth
says, in a news release. "If we don't burn that energy through regular
physical activity the body makes it a priority to store that energy as
48-Hour Exercise Window
Kump and Booth studied adolescent rats. When given exercise wheels, these
teen rats grew much stronger than rats that didn't have exercise wheels.
But when the rats were kept from exercising -- Kump and Booth locked the
exercise wheels for various lengths of time -- their bodies started to
The body changes came astonishingly fast. Just five hours after exercise
stopped, the rat's abdominal fat cells started to send off chemical signals
that made them start to swell. After two days of no exercise, the fat cells got
19% larger -- and the rats' stomach fat got 48% heavier.
This, Kump and Booth suggest, is just like what happens when people become
couch potatoes. What's surprising is how very fast it happens. On the other
hand, regular exercise offers a solution.
"We eat regularly, and we need to exercise regularly," Kump says in
a news release. "There is a magic bullet for keeping weight down. It's
daily physical activity."
A Warning for Teens
The teen rats that didn't exercise were much punier than those that did.
Kump and Booth say this is a warning for humans. If kids stop getting daily
exercise when they reach adolescence, they suggest, they may never develop
proper muscle mass.
Muscle is, of course, the body's main way of using up excess energy stored
as fat. Kids who don't add a lot of muscle during their teen years may be
doomed to add a lot of fat during adulthood.
The findings appear in the online edition of the Journal of