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Which of the following recommendations best applies to a 40-year-old
obese woman on a calorie-restricted diet for weight reduction?
1. High intensity exercise for at least 60 min/day will provide better
weight loss than moderate intensity exercise for 60 min/day
2. Moderate intensity exercise at 30 min/day is
as efficacious for weight loss as vigorous intensity exercise for the
same duration
3. Moderate intensity exercise performed for less than 30 min/day is
of no benefit in weight loss
4. Any exercise for any amount of time will provide significant weight
loss
Sept. 9, 2003 — Moderate intensity exercise is as good as vigorous
exercise for reducing weight in sedentary women, according to the results
of a randomized trial published in the Sept. 10 issue of The Journal
of the American Medical Association. A second study from the Women's
Health Initiative also suggests that vigorous exercise may be no better
than moderate intensity exercise in preventing breast cancer.
"Participants randomized to vigorous exercise intensity did not
have greater weight loss than those randomized to a similar dose of
exercise performed at a moderate intensity," write John M. Jakicic,
PhD, from the University of Pittsburgh in Pennsylvania, and colleagues.
"The results of this study have implications for prescription of
exercise for sedentary, overweight adults engaging in weight loss efforts."
From January 2000 through December 2001, 201 sedentary, overweight women
in a university-based weight control program were randomized to one
of four exercise groups based on the estimated energy expenditure (1,000
kcal/week or 2,000 kcal/wk) and exercise intensity (moderate or vigorous).
Moderate exercise duration was defined as about 150 min/week, and high
as about 200 min/week. All women were asked to restrict energy intake
to 1,200-1,500 kcal/day and dietary fat to 20% to 30% of total energy
intake.
At study entry, average age was 37 years, and average body mass index
(BMI) was 32.7. Of 201 women enrolled, 184 completed 12 months of treatment.
Average weight loss was about 8% to 10% of baseline body weight, and
it was not significantly different between groups (8.9 kg for vigorous
intensity/high duration, 8.2 kg for moderate intensity/high duration,
6.3 kg for moderate intensity/moderate duration, and 7.0 kg for vigorous
intensity/moderate duration).
Mean cardiorespiratory fitness levels also increased significantly in
all groups, with no significant difference between groups (22.0% for
vigorous intensity/high duration, 14.9% for moderate intensity/high
duration, 13.5% for moderate intensity/moderate duration, and 18.9%
for vigorous intensity/moderate duration).
"When data were analyzed based on the amount of exercise performed,
greater levels of exercise were associated with a greater magnitude
of weight loss following 12 months of treatment," the authors write.
"Thus, interventions should initially target the adoption and maintenance
of at least 150 min/wk of moderate intensity exercise, and when appropriate,
eventually progress to exercise levels consistent with the Institute
of Medicine's recommendation of 60 min/day."
The National Institutes of Health and the National Heart, Lung, and
Blood Institute supported this study.
In an accompanying editorial, I-Min Lee, MBBS, ScD, from Harvard Medical
School in Boston, Massachusetts, writes that these two studies suggest
that "modest and achievable levels of physical activity -- 30 min/d
on most days -- can decrease the risk of chronic disease including breast
cancer, and coupled with appropriate dietary restraint (this is crucial),
can help overweight women lose weight."
JAMA. 2003;290:1323-1330, 1377-1379
Clinical Context
Recent recommendations from the Centers for Disease Control and Prevention
and the American College of Sports Medicine have suggested a minimum
of 30 minutes of moderate-intensity activity on most days of the week
(150 min/week or moderate duration) to improve health and prevent cardiovascular
disease and mortality. This appears to contradict the Institute of Medicine
(IOM) 2002 recommendation of at least 60 min/day (high duration) of
moderate-intensity exercise for most days of the week to control body
weight in adults with normal BMI.
An estimated two thirds of Americans are overweight and one third are
obese, making this the leading preventable cause of cardiovascular disease.
Nearly three quarters of women are sedentary compared with 64% of men.
However, fewer than one fifth of studies on the benefits of exercise
have been conducted on women.
This randomized one-year study of 201 sedentary overweight and obese
women (average BMI, 32.7) examines the effects of two levels of exercise
intensity and duration on weight loss and cardiorespiratory fitness
while on a calorie-restricted diet.
Study Highlights
201 overweight and obese women (BMI, 27-40) were recruited into a weight-loss
program with caloric restriction of 1,200 to 1,500 kcal/day, and randomized
into 4 exercise groups: (1) vigorous intensity/high duration exercise,
(2) moderate intensity/high duration exercise, (3) moderate intensity/moderate
duration exercise, and (4) vigorous intensity/moderate duration exercise.
The study was powered at 70% at an a of 0.05 to detect a difference
in outcomes between the 4 groups, assuming an attrition rate of 15%-20%.
Dropout rate was low, with 184 participants completing the 12-month
study.
Baseline characteristics include sedentary behavior (exercise less than
3 days/week for less than 20 minutes/day over the past 6 months); mean
age, 37 years; more than 50% of subjects had a college degree; most
had professional or clerical/technical employment (76%); and subjects
were predominantly white (81%), married (65%), and nonsmokers (92%).
There was no difference in baseline characteristics among groups.
The weight-loss intervention included a behavioral program with weekly
meetings for 24 weeks followed by biweekly meetings, and biweekly telephone
calls from month 7 to 12.
The exercise prescription had walking as the primary mode of exercise,
and intensity defined as vigorous or moderate by the percentage of age-predicted
maximal heart rate and rating of perceived intensity on the Borg scale.
Duration was defined as moderate (less than 150 min/week) or high (200
min/week or more).
Participant log of food frequency and exercise duration, intensity,
and type were used to track adherence to assigned protocol.
Primary outcomes were weight loss, weight percentage change from baseline,
and cardiorespiratory fitness measured as percentage increase in oxygen
consumption (mL/kg/min) and time to achieve 85% of maximum heart rate
on a treadmill test at 6 and 12 months compared with baseline.
Weight loss was significant for all groups, and at 12 months averaged
8% to 10% of baseline body weight. There was no significant effect of
either duration or intensity of exercise on changes in weight or BMI
among the four groups.
Cardiorespiratory fitness improved for all groups at 6 and 12 months
compared with baseline, with percentage improvement in oxygen consumption
ranging from 14.9% to 22%, and no significant difference was seen among
groups.
Percentage change in cardiovascular fitness was greatest for the high
duration vs. moderate duration group (P < .007), but exercise intensity
had no effect on cardiorespiratory fitness.
Pearls for Practice
Moderate and vigorous intensity exercise are equally efficacious for
weight reduction and cardiorespiratory fitness in a one-year supervised
weight-loss program with caloric restriction.
High duration exercise (200 min/week or more) achieves greater cardiorespiratory
fitness but not greater weight loss compared with moderate duration
exercise (150 min/week), when combined with a calorie-reduced diet.
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