February 28 — 29, 2008 Advisory Committee Meeting
Minutes
Subcommittee Report: Energy Balance
Edward Howley, Ph.D., presented the energy balance subcommittee
report. Dr. Howley started with strong note that energy balance is equally
dependent on intake and expenditure and both sides must be addressed. The group
addressed the following research questions:
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How much physical activity is needed relative to: Weight
stability and weight loss; Weight regain following weight loss; Measures of
central adiposity.
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Do the following factors affect physical activity
recommendations for energy balance: Age and gender; Race/ethnicity and social
economic status (SES).
In reviewing the data the subcommittee defined weight
maintenance as less than 3% change in body weight and weight loss as more than a
5% reduction in body weight.
The cross-sectional evidence on physical activity and body
weight included 24 studies from the CDC database of which 22 showed favorable
effects of activity on weight. There was also a dose-response relationship with
most favorable changes occurring with 30 – 60 minutes per day of activity.
Prospective evidence included 9 studies all showing favorable effects with 30 –
45 minutes per day to reduce weight gain over time. RCT evidence included 19
studies of which 7 reported a significant effect.
Reviewing the effects of resistance exercise, 9 studies showed
modest change in body weight. The potential reasons for these modest effects
include weight loss may be accompanied by a concurrent increase in fat-free mass
and dose of resistance exercise may not be sufficient.
Overall conclusions for weight loss and maintenance suggest that
endurance activities show a clear dose-response across studies with a range of
180 – 360 minutes per week over 12 weeks to 18 months results in weight loss of
3kg or less. Resistance exercises show a magnitude of 1kg or less of weight
loss. It is important to note that dietary intervention is also necessary.
To analyze physical activity and weight regain following weight
loss the group identified 8 RCT studies with only 3 studies randomizing subjects
to physical activity levels subsequent to weight loss and only 2 used a control
group. Three observational studies were identified. From this data one can
conclude that “more is better.” The estimated gross energy expenditure needed
for weight maintenance after weight loss is the equivalent to 60 minutes at
approximately 4mph or 80 minutes at approximately 3mph.
Researching the relationship between physical activity and body
composition related to metabolic disorders the subcommittee reviewed RCT
studies. Both aerobic and resistance training favorably affected body
composition. Abdominal fat loss is proportional to overall fat loss, and is
greater in overweight individuals. 45 – 60 minutes per day of
moderate-to-vigorous activity is needed for clinically relevant changes in total
and abdominal adiposity.
The subcommittees report on the relationship between physical
activity, energy balance and gender and age included cross-sectional and
prospective studies, RCTs, epidemiological studies as well as observational
studies. There is some evidence that the amount of physical activity needed to
maintain weight increases with age and may be higher for women; however, the
evidence is not sufficient to recommend differential prescriptions based on
gender or age alone.
Addressing the effect of race/ethnicity and SES, Dr. Howley
noted there are a few studies on Latinos and American Indians; however,
heterogeneity both between and within racial/ethnic croups limits extrapolation
of results. The limited amount of data makes it unwise to draw conclusions as to
whether physical activity recommendations should differ by race, ethnicity or
SES.
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