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DURHAM, N.C. -- The results of a Duke University Medical
Center randomized controlled trial strongly suggests that not
only can 30 minutes of daily walking prevent weight gain in
most sedentary people, but that any further exercise can lead
to additional loss of weight and fat.

The researchers said that their study provides the first
scientific basis for a "more is better" approach to exercise.
The 30 minutes of daily walking is the equivalent of 10 to 12
miles of walking each week, the researchers said, adding that
for most sedentary people, this amount of exercise will offset
the slow and incremental weight gain of inactivity.

The results of the Duke study were published Jan. 12, 2004,
in the Archives of Internal Medicine.

The Duke team enrolled overweight and sedentary adults into
a program of three escalating levels of exercise for more than
eight months. Since the purpose of the trial was only to gauge
the effects of different amounts and intensities of exercise,
participants were encouraged not to change their normal diet.
The main measurements were changes in weight, body composition
and waist circumference.

"We found that the two low-exercise groups lost both weight
and fat, while those in the more intensive group lost more of
each in a 'dose-response' manner," said Cris Slentz, Ph.D.
"Simply put, the more you exercise, the more you benefit. Just
as importantly, the control group of participants who performed
no exercise gained weight over the period of the trial."

"From the perspective of prevention, it appears that the 30
minutes per day will keep most people from gaining the
additional weight associated with inactivity," Slentz said.
"Given the increase in obesity in the U.S., it would seem
likely that many in our society may have fallen below this
minimal level of physical activity required to maintain body
weight."

The Duke study was supported by a $4.3 million grant from
the National Heart, Lung and Blood Institute. The trial, dubbed
STRRIDE (Studies of Targeted Risk Reduction Interventions
through Defined Exercise), was led by Duke cardiologist William
Kraus, M.D.

Since the ability of exercise to lower weight and fat was
demonstrated without any changes in diet, the researchers also
believe a focus on dietary intake can only add to the benefits
of exercise in reducing weight.

For the trial, researchers randomized 120 participants into
one of four groups: no exercise, low dose/moderate intensity
(equivalent of 12 miles of walking per week), low dose/vigorous
intensity (equivalent of 12 miles of jogging per week) or high
dose/vigorous intensity (equivalent of 20 miles of jogging per
week). The exercise was carried out on treadmills, elliptical
trainers or cycle ergometers in a supervised setting.

Participants in the high dose/vigorous intensity group saw
reductions in all measures when compared to the two lower
exercise and control groups.

Specifically, the high dose/vigorous intensity group
experienced a 3.5 percent weight loss, while the two low-dose
exercise groups experienced slightly greater than a 1 percent
weight loss. During the same period, the inactive control group
showed a 1.1 percent weight gain.

Interestingly, the two vigorous intensity groups saw similar
increases in lean body mass, or muscle, which were twice as
high as the 0.7 percent increase for the low-intensity
group.

"The higher exercise intensity groups resulted in greater
increases in lean body mass, which if confirmed by other
studies, could have significant implications," Slentz said.
"This finding suggests that while the amount of exercise
determines total body weight change and fat mass loss, exercise
intensity would appear to be the primary determinant of gain in
lean body mass."

In terms of body fat mass, the inactive group experienced a
0.5 percent increase, while all the exercise groups saw
important decreases: 2 percent decrease for low dose/moderate
intensity; 2.6 percent decrease for low amount/vigorous
intensity; and 4.9 percent decrease for high dose/vigorous
intensity.

"This study revealed a clear dose-response effect between
the amount of exercise and decreases in measurements of central
obesity and total body fat mass, reversing the effects seen in
the inactive group," Slentz said. "The close relationship
between central body fat and cardiovascular disease, diabetes
and hypertension lends further importance to this finding."

Participants who did not exercise experienced an average 0.8
percent increase in waist circumference, while all the exercise
groups saw decreases: 1.6 percent decrease for low
dose/moderate intensity; 1.4 percent decrease for low
amount/vigorous intensity; and 3.4 percent decrease for high
dose/vigorous intensity.

Joining Slentz were Duke colleagues Brian Duscha, Johanna
Johnson, Kevin Ketchum, Lori Aiken, Gregory Samsa, Ph.D., and
Connie Bales, Ph.D. Joseph Houmard, Ph.D., East Carolina
University, was also a member of the team.