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3
Physical Activity, Obesity,
and Weight Management
The effects of physical activity have been investigated in relation to
weight loss, weight loss maintenance, and the prevention of weight gain.
This workshop session included a presentation on those topics followed
by a discussion period. This chapter includes a review of the evidence on
effects of physical activity in weight management; a brief discussion of
aging, inactivity, and obesity; additional information from epidemiologi-
cal studies; and a brief summary of major points raised during the group
discussion.
EFFECTS OF PHYSICAL ACTIVITY ON WEIGHT LOSS,
WEIGHT LOSS MAINTENANCE, AND THE PREVENTION
OF WEIGHT GAIN
Presenter: Joseph E. Donnelly
This presentation provided background information on physical ac-
tivity and weight management, and also addressed various types of evi-
dence related to physical activity for weight loss and for the prevention
of weight gain.
Background
The general concept of physical activity and weight management is
straightforward:
59
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60 PHYSICAL ACTIVITY WORKSHOP
• Physical activity expends energy
• Energy expenditure can produce a negative energy balance
• Weight loss occurs during a negative energy balance
Many compensatory mechanisms can occur, however, when one in-
creases physical activity. These include changes in diet, spontaneous ac-
tivity, resting metabolism, and others. Thus an important question is how
to create an energy gap that is effective for weight management (includ-
ing weight maintenance or weight loss).
Evidence that Physical Activity Will Alter Energy
Balance and Provide Weight Loss
Many population studies show that measures of body fat status are
lower among those with higher physical activity levels. For example,
using data from a population survey, Holcomb et al. (2004) showed that
body mass index (BMI), percentage body fat, and waist-to-hip ratio each
decreased with an increasing level of physical activity.
A number of meta-analyses have shown that the amount of weight
lost with increases in physical activity tends to be small, and it is greater
for men than for women. Ballor and Keesey (1991) conducted a meta-
analysis of exercise and weight loss that included 53 studies. With an
energy expenditure of nearly 1,500 kilocalories (kcal) per week from
exercise for men, their mean weight loss was approximately 1.4 kilo-
grams (kg) after approximately 16 weeks. The women had a mean en-
ergy expenditure of more than 900 kcal per week from exercise, and their
mean weight loss was less than 1 kg after about 11 weeks. A similar
meta-analysis by Garrow and Summerbell (1994) covering eight random-
ized controlled trials (five for men and three for women) found slightly
greater weight loss, but the results were very similar.
Does an exercise intervention alone lead to weight loss? Studies of
Targeted Risk Reduction Interventions through Defined Exercise
(STRRIDE) examined this question in an 8-month randomized controlled
trial of overweight untrained adults (Slentz et al., 2004). The investiga-
tors treated overweight persons with three different levels of exercise but
instructed them not to change their diet. The control group gained about
1 kg; the low-amount, moderate-intensity exercise group (equivalent to
walking approximately 12 miles/week) and the low-amount, vigorous-
intensity exercise group (equivalent to jogging approximately 12
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OBESITY AND WEIGHT MANAGEMENT
miles/week) lost about 1 kg. The high-amount, vigorous-intensity exer-
cise group (equivalent to jogging approximately 20 miles/week) lost
about 3.5 kg on average—4 percent of their body weight. This latter
amount approaches clinical significance with regard to health benefits.
Slentz et al. (2004) examined weight change per mile of exercise and
estimated that covering a distance of about 6 miles/week corresponds
with the amount of exercise that results in weight maintenance.
In a supervised study in which subjects came into the laboratory,
Ross and colleagues (2000, 2004) found that a 500- to 700-kcal deficit
per day, either through diet or exercise, produced a 6.5 percent weight
loss for women and an 8 percent weight loss for men over a 12-week
period.
In the 16-month, supervised Midwest Exercise Trial, Donnelly et al.
(2003) found, using objective measures, that the men expended approxi-
mately 300 kcal more per session than did the women when prescribed
the same relative amount of exercise in terms of frequency, intensity, and
duration. With ad libitum eating, the men lost, on average, about 5 per-
cent of their baseline weight within about 9 months. In contrast, the
women did not lose weight; however, they gained little or no weight on
average over the 16 months. Individual variation was substantial, espe-
cially for the women. All but one of the men in the Midwest Exercise
Trial lost weight, in varying amounts, but only half of the women lost
weight. As also discussed later in the session by Dr. Glenn Gaesser, other
studies have produced the results illustrated in Figure 3-1.
Evidence that Physical Activity Will Benefit Weight
Maintenance Among Persons Who Have Lost Weight
Qualitative evidence from the National Weight Control Registry
(Klem et al., 1997) suggests that the levels of physical activity required
to maintain weight following a substantial weight loss are higher than
many people realize—more than 2,500 kcal/week. Weight management
programs suggest that approximately 300 minutes of exercise are needed
per week to produce weight maintenance for one year (LeCheminant et
al., 2005).
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62 PHYSICAL ACTIVITY WORKSHOP
10
Gainers (N = 11)
Change in body fat (kg)
5
0
–5
Losers (N = 20)
–10
Subjects
FIGURE 3-1 Individual variation in body fat mass change in response to aero-
bic exercise training in obese women.
SOURCE: Lamarche et al. (1992). Reprinted from Metabolism 41(11), La-
marche et al., Is body fat loss a determinant factor in the improvement of carbo-
hydrate and lipid metabolism following aerobic exercise training in obese
women? Pp. 1249–1256, 1992, with permission from Elsevier.
A dose–response effect was demonstrated in a study by Jakicic et al.
(1999). After weight loss at 6 months, weight was maintained for 6
months by those exercising more than 200 minutes per week, whereas
those exercising less than 150 minutes per week experienced regain of
weight. More recent work by Jakicic and colleagues (John M. Jakicic,
University of Pittsburgh, personal communication, October 16, 2006)
indicates that physical activity levels were substantially higher for those
who maintained a weight loss of at least 10 percent of their body weight
for 18 months than for those who did not maintain that degree of weight
loss.
Dr. Donnelly indicated that the randomization in most studies is done
at baseline. However, randomization after weight loss is the correct study
design but is rarely used. Jeffery et al. (2003) randomized subjects at
baseline and at the beginning of the period of testing interventions to
maintain weight. Subjects randomized to the 2,500 kcal/week exercise
group maintained weight better, on average, than did those in the 1,000
kcal/week exercise group (Figure 3-2). Although there was considerable
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OBESITY AND WEIGHT MANAGEMENT
variation in exercise levels, the subjects who were asked to do more ex-
ercise did more exercise.
In a study by Borg et al. (2002) in which men were randomized after
weight loss either to control or exercise groups for 6 months, a physical
activity energy expenditure of approximately 2,400 kcal/week was asso-
ciated with the maintenance of weight loss.
Three additional studies were found in which subjects were random-
ized after weight loss. In the study by Perri et al. (1988), all groups did
better than the controls; but the groups assigned to behavior plus exercise
did no better than the behavioral groups at 18 months. Leermakers and
colleagues (1999) found that after 6 months, weight regain was lower
among the exercise plus behavioral strategies group than among the
group with exercise but no behavioral strategies. A somewhat con-
founded 24-month study by Fogelholm et al. (2000) found less weight
regain among those in the 1,000 kcal/week exercise group than in the
Baseline 6 months 12 months 18 months
0
-5
-10
Pounds
-15
-20 1,000 kcal
2,500 kcal
-25
FIGURE 3-2 Mean weight change over time by treatment group.
NOTES: ♦ = standard behavior therapy (SBT) group with a goal of expending
1,000 extra kilocalories per week; ■ = high physical activity (HPA) treatment
group with a goal of expending 2,500 extra kilocalories per week. SBT group
marginally different from the HPA group at 12 months (p = .07) and signifi-
cantly different at 18 months (p = .04).
SOURCE: Jeffery et al. (2003). Adapted, with permission, from The American
Journal of Clinical Nutrition.
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64 PHYSICAL ACTIVITY WORKSHOP
control group. There was no difference, however, between the 2,000
kcal/week exercise group and the controls, perhaps suggesting attrition
problems. This suggests a benefit–risk question: Is it better to get a lower
level of exercise for many years or a higher level of exercise with the risk
of greater attrition?
Evidence on Physical Activity in the
Prevention of Weight Gain
Dr. Donnelly presented evidence to support his position that rela-
tively small amounts of physical activity may be sufficient to enable
people to prevent unhealthy weight gain. Some investigators suggest that
people gain weight in episodes related to life events such as marriage and
having children, and others use a more linear perspective. Hill et al.
(2003), for example, using data from the National Health and Nutrition
Examination Survey and from the Coronary Artery Risk Development in
Young Adults study, concluded that the energy gap for approximately 50
percent of the population may be as small as 15 kcal/day, and that speci-
fying a gap of 50 kcal/day would cover about 90 percent of the popula-
tion. Hill uses a value of 100 kcal/day to represent the energy gap, but it
is acknowledged that currently there is little experimental data to support
this value.
In an 18-month study with middle-aged women, Donnelly et al.
(2000) showed that either 30 minutes of supervised continuous exercise
three times a week or two 10- to 15-minute bouts of supervised exercise
5 days per week prevented weight gain without a dietary intervention.
Dunn et al. (1999) found that sedentary men and women randomized
either to lifestyle or structured exercise groups, with a goal of 1,000 kcal
of energy expenditure per week, gained little or no weight in the 2-year
intervention period.1
In an ongoing study (John M. Jakicic, University of Pittsburgh, per-
sonal communication, October 16, 2006), preliminary data show that
after 18 months, subjects assigned to either 150 minutes or 300 minutes
of physical activity per week weighed about 1 kilogram less than at base-
line. If confirmed, this finding suggests that small amounts of physical
activity may be sufficient to maintain the weight of persons who have not
recently undergone a period of weight loss.
1
Dr. Blair noted later that actual energy expenditure was only about 65 kcal/day.
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OBESITY AND WEIGHT MANAGEMENT
Concluding Remarks
Physical activity or weight loss creates a relatively small energy gap
and cannot be expected to provide the weight loss that is seen with en-
ergy restriction. Effects appear to differ for men and women, and there
are responders and nonresponders. Dr. Donnelly took the position that
the time and amount of energy expenditure required for the prevention of
unhealthy weight gain appears to be 15 to 30 minutes/day or about 700 to
1,000 kcal/week. The amount of physical activity needed to achieve the
loss of 5 percent of one’s body weight appears to be about 45 min-
utes/day or 2,000 to 2,500 kcal/week. For weight-loss maintenance, the
amount of physical activity required is likely to be similar to, or perhaps
greater than, that for weight loss.
DISCUSSION
Aging, Inactivity, and Obesity
Discussant: Andrew Goldberg
Predictors of obesity and weight regain include high caloric intake,
physical inactivity, low resting metabolic rate, low fat oxidation, reduced
muscle mass, aging, decreased insulin sensitivity, and perhaps elevated
adipose lipoprotein lipase activity (Ravussin and Swinburn, 1993). Aging
is associated with a decline in energy expenditure, which when not com-
pensated by a reduction in caloric intake, leads to weight gain. Regular
physical activity will increase energy expenditure for older people. Main-
taining energy balance with aging is critical to prevent obesity and
weight regain following successful weight loss.
Studies in postmenopausal women by Goldberg and colleagues
(Nicklas et al., 1996) show that weight loss, when combined with exer-
cise training, blunts the decline in resting metabolic rate and in fat
oxidation observed with weight loss alone. Dr. Goldberg’s group has
shown that weight loss plus an increase in VO2max of greater than 5 per-
cent results in several health benefits, including reductions in intra-
abdominal fat and insulin resistance; improvements in glucose tolerance,
insulin sensitivity, and blood pressure; reductions in total and low
density lipoprotein cholesterol and triglycerides; and increases in
high density lipoprotein cholesterol (Lynch et al., 2001).
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66 PHYSICAL ACTIVITY WORKSHOP
A study by Bunyard et al. (1998) shows that both obese and lean
sedentary middle-aged men were able to increase their exercise capacity
by 15 percent with an aerobic exercise program. The lean sedentary
group lost about 1.8 kg after 6 months of training despite increasing their
caloric intake, and the obese sedentary men lost about 8 kg after 6
months of the exercise training plus hypocaloric weight loss instruction.
Master athletes who discontinued exercise training for 8 weeks experi-
enced a reduction in VO2max of about 15 percent and gained about 0.5
kg, despite reducing their caloric intake by 17 percent. All groups con-
verged to about the same level of fitness, but when placed on isocaloric
weight maintaining diets, the obese and lean men were able to consume 5
percent and 8 percent more calories, respectively, without gaining
weight. These results provide evidence that sedentary older people can
change their daily exercise habits to increase their energy expenditure
from physical activity, allowing them to eat more without gaining
weight. Thus regular aerobic exercise, by increasing daily energy expen-
diture, may counter the age-related tendency toward obesity and its asso-
ciated cardiovascular risk factors.
Preliminary studies are in progress in Dr. Goldberg’s laboratory to
test the hypothesis that weight loss, when combined with aerobic exer-
cise training, will maintain both the resting metabolic rate and the oxida-
tion of fat and carbohydrate, with subsequent cardiometabolic and weight
maintenance benefits (Ortmeyer et al., 2006). This hypothesis is illus-
trated in Figure 3-3. Our understanding of the potential benefits of exer-
cise training for weight management in obese middle-aged and older
people may be enhanced by knowledge of the metabolic mechanisms by
which exercise, when combined with weight loss, increases fat and car-
bohydrate oxidation in muscle.
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OBESITY AND WEIGHT MANAGEMENT
Weight Loss Weight Loss + Exercise
RMR RMR
Fat and CHO OX Fat and CHO OX
LPL
LPL
LPL
LPL
CPT-1 CPT-1
GS GS
Insulin sensitivity (M) Insulin sensitivity (M)
Lipid partitioning/utilization Lipid partitioning/utilization
Cardiometabolic benefit Cardiometabolic benefit
Weight regain Weight regain
FIGURE 3-3 Hypothesis: Metabolic adaptations to weight loss with or without
aerobic exercise.
NOTE: RMR=resting metabolic rate; CHO=carbohydrate; OX=oxidation;
LPL=lipoprotein lipase; CPT-1=carnitine palmitoyltransferase-1; GS=glycogen
synthase.
SOURCE: Goldberg (2006).
Additional Epidemiological Data on
Physical Activity and Weight
Discussant: Glenn Gaesser
As the prevalence of obesity has risen, so have weight loss at-
tempts—without much apparent success. Epidemiological studies of
women and men in the United States indicate a tendency for an inverse
relationship between BMI and physical activity (Feskanich et al., 2002;
Hu et al., 1999; Kushi et al., 1997). Studies in a number of other coun-
tries show mixed findings, with most showing an inverse relationship
between BMI and physical activity for men (Andersen et al., 2000; Hu et
al., 2003; Rosengren and Wilhemsen, 1997; Thune et al., 1998) and
women (Andersen et al., 2000; Hu et al., 2003; Mensink et al., 1999).
However, some studies show no relationship for men (Bijnen et al.,
1998; Smith et al., 2000) or for women (Thune et al., 1998). In studies
reporting the strongest inverse associations between BMI and physical
activity, the mean BMI is no more than one to two BMI units lower for
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68 PHYSICAL ACTIVITY WORKSHOP
those at a high physical activity level than for those at a low physical
activity level (Feskanich et al., 2002; Hu et al., 1999, 2003; Kushi et al.,
1997).
Data from Rosell et al. (2006) indicate that weight gain tended to be
modestly less for more active than for less active persons over a 5-year
period. Petrella et al. (2005) reported similar findings of a modest benefit
of physical activity over a 10-year period among older persons. Notably,
compared to weight change in younger persons, change in weight tends
to be of smaller magnitude in older individuals.
Larmarche et al. (1992) demonstrated that, among obese women who
participated in exercise training, both those who lost fat and those who
gained fat had improvements in VO2max, glucose tolerance, and blood
lipid concentrations. Thus, regardless of the response measured by
weight change or body fat change, individuals in the exercise program
responded favorably in terms of indicators of health. Earlier work by
Bjorntorp et al. (1970) found improvement in insulin sensitivity after
exercise training with an increase in body fat.
In summary, cohort studies reveal an inverse association between
physical activity and BMI, but the effect is relatively small. Physical ac-
tivity may be more effective in preventing unhealthy weight gain than in
producing weight loss. Many weight-related health problems can be im-
proved with exercise independently of weight loss. This latter point mer-
its emphasis in view of the very modest effect of exercise on inducing
weight change in women.
Group Discussion
Moderator: Peter Brubaker
During the group discussion, workshop presenters and other partici-
pants raised the following points:
• Walking and running the same distance are not actually equiva-
lent in energy expenditure. Several persons suggested that point-
ing out the discrepancy would be counterproductive because the
concept is difficult to understand.
• Despite the modest effect of physical activity on weight loss,
certain health benefits do not occur without a physical activity
component of treatment.
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OBESITY AND WEIGHT MANAGEMENT
• Maintenance of healthy weight when children are growing is a
very important focus. Factors involved include physical educa-
tion programs, allowed recess activities, extracurricular activi-
ties, and potentially, short bouts of physical activity in the
classroom.
• Research in older disabled people has found that a moderate in-
crease in VO2max leads to marked improvements in glucose me-
tabolism, insulin levels, and glucose tolerance, implying benefit
for older people in general.
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Representative terms from entire chapter:
weight loss
