Author Affiliations: Physical Activity and Weight Management Research Center, University of Pittsburgh, Pennsylvania (Dr Jakicic and Ms Janney); Centers for Behavioral and Preventive Medicine, Brown Medical School and The Miriam Hospital, Providence, Rhode Island (Dr Marcus); and Department of Biostatistical Sciences, Wake Forest University, Winston-Salem, North Carolina (Dr Lang).
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Debate remains regarding the amount of physical activity that will facilitate weight loss maintenance.
Between December 1, 1999, and January 31, 2003, 201 overweight and obese women (body mass index [calculated as weight in kilograms divided by height in meters squared], 27 to 40; age range, 21-45 years) with no contraindications to weight loss or physical activity were recruited from a hospital-based weight loss research center. Participants were assigned to 1 of 4 behavioral weight loss intervention groups. They were randomly assigned to groups based on physical activity energy expenditure (1000 vs 2000 kcal/wk) and intensity (moderate vs vigorous). Participants also were told to reduce intake to 1200 to 1500 kcal/d. A combination of in-person conversations and telephone calls were conducted during the 24-month study period.
Weight loss did not differ among the randomized groups at 6 months' (8%-10% of initial body weight) or 24 months' (5% of initial body weight) follow-up. Post-hoc analysis showed that individuals sustaining a loss of 10% or more of initial body weight at 24 months reported performing more physical activity (1835 kcal/wk or 275 min/wk) compared with those sustaining a weight loss of less than 10% of initial body weight (P < .001).
The addition of 275 mins/wk of physical activity, in combination with a reduction in energy intake, is important in allowing overweight women to sustain a weight loss of more than 10%. Interventions to facilitate this level of physical activity are needed.
clinicaltrials.gov Identifier: NCT00006315.
More than 65% of adults in the United States are overweight,1 which is a public health concern because of its association with numerous chronic diseases.2 Among obese adults, long-term weight loss and prevention of weight regain have been less than desired.3,4 Therefore, there is a need for more effective interventions.
Behavioral interventions, including a reduction in energy intake (diet) and an increase in energy expenditure (exercise/physical activity), result in weight loss of approximately 10% of initial body weight within 6 months.5 The importance of physical activity may be heightened in the maintenance of clinically significant weight loss.6- 9
The consensus on recommendations for physical activity is a minimum of 30 minutes of moderate intensity activity on most days of the week, or 150 min/wk.10,11 There is growing consensus that more exercise may be necessary to enhance long-term weight loss.12- 15 Few studies exceeding 12 months in duration have been conducted to examine the optimal amount of exercise to enhance weight loss. In secondary analyses, Jakicic et al6 reported that exercise for longer than 200 min/wk during a 12-month period enhanced weight loss, and data through 24 months are presented in this article.
This study examined the effect of exercise of varying duration and intensity on weight loss and fitness in overweight adult women during a 24-month period. Secondary analyses examine the amount and intensity of exercise necessary to sustain varying levels of weight loss at 24 months' follow-up.
Data collection and the study intervention were conducted from December 1, 1999, until January 31, 2003. Participants included 201 women (Table 1 and Figure 1) who met the following eligibility criteria: having a body mass index (calculated as weight in kilograms divided by height in meters squared) of 27 to 40, being 21 to 45 years old, and being sedentary at baseline, defined as reporting exercising fewer than 3 d/wk for less than 20 min/d during the previous 6 months. Exclusionary criteria included history of myocardial infarction, taking medication that would alter the heart rate response during exercise, taking medication that would affect metabolism or weight loss, being treated for psychological conditions, being pregnant currently or within the past 6 months or planning to become pregnant during the intervention period, having a medical condition that affects metabolism or body weight, or having a medical condition that would limit exercise participation. A medical history and physical activity readiness questionnaire (PAR-Q)16 were completed, and each participant's personal physician indicated that the proposed intervention was not contraindicated. Written informed consent was obtained, and the protocol was approved by the institutional review boards of The Miriam Hospital and the University of Pittsburgh.
Participant randomization and follow-up.
Participants attended group meetings weekly during months 1 to 6, twice per month during months 7 to 12, and once per month during months 13 to 18. No group sessions were conducted during months 19 to 24. Sessions focused on strategies for modifying eating and exercise behaviors.
Subjects received brief (approximately 10 minutes long) telephone calls periodically from a member of the intervention team. A standard script was used to conduct these calls. Telephone calls occurred twice per month during months 7 to 12, once per month during months 13 to 18, and twice per month during months 19 to 24.
Subjects weighing less than 90 kg at baseline were prescribed energy intake of 1200 kcal/d, and subjects weighing 90 kg or more at baseline were prescribed 1500 kcal/d. The prescribed dietary fat intake was 20% to 30% of total energy intake. Subjects were instructed to maintain these dietary recommendations throughout the study period unless they achieved a body mass index of less than 25, at which time energy intake was adjusted.
Subjects were randomized to 1 of 4 exercise conditions based on estimated energy expenditure (moderate, 1000 kcal/wk; high, 2000 kcal/wk) and exercise intensity (moderate vs vigorous).6 Randomization, based on a computer program (SPSS statistical software; SPSS Inc, Chicago, Illinois), was to moderate intensity/moderate energy expenditure, moderate intensity/high energy expenditure, vigorous intensity/moderate energy expenditure, or vigorous intensity/high energy expenditure. Energy expenditure was converted to minutes per week based on the average body weight of participants in this study, and weekly goals for participants were expressed in minutes per week. Participants were encouraged to spread the exercise over 5 d/wk and to exercise for a minimum of 10 minutes each time. Intensity was prescribed as percentage of age-predicted maximal heart rate (moderate, 50%-65%; vigorous, 70%-85%) and rating of perceived exertion (moderate, 10-12; vigorous, 13-15).16 Participants were taught how to monitor their heart rate using the palpation method and how to regulate intensity using the rating of perceived exertion. Exercise was not supervised on site, but a treadmill was provided to each subject to use at home as a strategy to enhance participation.7
Height was measured at baseline to the nearest 0.1 cm. Subjects were weighed at baseline and at 6, 12, 18, and 24 months' follow-up in undergarments while wearing a cloth hospital gown to the nearest 0.11 kg.
Waist circumference, measured horizontally at the umbilicus; hip circumference, measured at the widest portion of the buttocks; and sagittal diameter of the abdomen, measured at the iliac crest in a supine position, were measured at 0, 6, and 24 months. Measurements were accepted when 2 measurements of 2.0 cm or less apart were obtained.
A submaximal graded exercise treadmill test to 85% of age-predicted maximal heart rate (computed as 220 − age in years) was performed at 0, 6, and 24 months. Speed was 80.4 miles/min (3.0 mph); grade was initiated at 0% and progressed by 2.5% at 3-minute intervals until the termination heart rate was achieved. A metabolic cart (Vmax Spectra; SensorMedics, Yorba Linda, California) was used to assess oxygen consumption.
We assessed leisure-time physical activity (LTPA) using a questionnaire.17 This questionnaire was completed by participants at baseline and at 6 and 24 months. However, a subsample of participants also completed this questionnaire at 12 and 18 months. Energy expenditure was computed using previously published scoring algorithms17 and classifications based on the compendium of physical activity.18 This questionnaire queried subjects about the amount of walking (12 city blocks equivalent to 1 mile and 1 mile equivalent to 20 minutes), along with time spent per week in sport, fitness, or recreational activity performed for the purpose of exercise. These data were used to represent time (minutes per week) and energy expenditure (kilocalories per week) for participation in LTPA. Subjects also reported flights of steps walked per day; however, data from the flights of steps reported were not used in the computation of LTPA for this study.
Energy intake was assessed at 0, 6, and 24 months using the previously validated 1998 version of the food frequency questionnaire developed by Block et al.19
Eating behavior was assessed at 0, 6, and 24 months using the Eating Behavior Inventory.20 A higher score is indicative of engagement in more eating behaviors recommended for weight control.
A power calculation was computed based on expected changes in body weight between the randomized groups. Randomization of 40 subjects per group provided 70% power to detect a moderate effect size (0.50) for differences in weight loss between the groups at an α level of .05 assuming moderate intraclass correlations (0.40-0.60) among the repeated measures (time effect). Assuming a 15% to 20% attrition rate increased the sample to 50 subjects per randomized group.
Statistical analyses were performed using SAS statistical software, version 9.1 (SAS Institute Inc, Cary, North Carolina), and SPSS statistical software, version 15.0 (SPSS Inc, Chicago, Illinois), with the type I error rate fixed at P ≤ .05 (2-tailed). Separate mixed-effect models were performed to examine the change in selected outcomes across the 24-month study period. These were intention-to-treat analyses with baseline data carried forward for missing data at subsequent assessment periods.
This study randomly assigned 201 subjects to the intervention. However, 10 subjects were excluded from follow-up analyses because of pregnancy (n = 9) and non–study-related death (n = 1). Thus, 191 subjects were included in the primary analyses performed to examine the a priori aims of this study.
Secondary analyses were performed with subjects grouped based on the percentage weight loss achieved at 24 months' follow-up and included 170 subjects who provided objective weight loss data at 24 months. Weight loss categories were less than 0% (n = 54), 0% to 4.9% (n = 33), 5.0% to 9.9% (n = 36), and 10% or more (n = 47) of initial body weight.
Baseline characteristics did not differ among participants randomly assigned to the 4 exercise groups (Table 1). Of 191 randomized participants, 170 (89.0%) completed the 24-month study (Figure 1). There were no serious adverse effects related to the study interventions. Our χ2 analysis revealed no significant difference in completion rates among groups (moderate intensity/moderate energy expenditure, 82.9%; moderate intensity/high energy expenditure, 89.1%; vigorous intensity/moderate energy expenditure, 90.0%; vigorous intensity/high energy expenditure, 93.7%). Subjects who completed the study were significantly older than those who did not (mean [SD] age, 38.3 [5.4] vs 33.8 [4.3] years; P < .001). No other differences were observed at baseline. Data are given throughout as mean (SD).
Subjects attended 79.1% (19.5%) of the group sessions during months 1 to 6, and mean attendance was 67.8% (22.0%) of group sessions for the entire 24-month period. During the study, 67.7% (23.7%) of telephone calls were completed during the intervention period. There were no significant differences between intervention groups for sessions attended or telephone calls completed.
The significant time effect for LTPA reflects an increase of 1235 (1815) kcal/wk from baseline to 6 months' follow-up (Table 2). This increase was not sustained, and the increase at 24 months' follow-up was 720 (1189) kcal/wk above baseline. The nonsignificant group × time interaction indicated that this pattern for LTPA was consistent across intervention groups. Eating behavior and dietary intake data are presented in Table 2.
Weight loss data are shown in Table 3 and Figure 2. There was a significant time effect (P < .001) for change in body weight and a nonsignificant group effect and group × time interaction effect. Weight loss was 8.1 (5.0) kg (9.3% [5.6%] of initial body weight) at 6 months' follow-up, 7.8 (6.8) kg (8.9% [7.8%] of initial body weight) at 12 months, 5.9 (7.0) kg (6.8 [8.1%] of initial body weight) at 18 months, and 4.2 (7.2) kg (5.0% [8.5%] of initial body weight) at 24 months. Anthropometric data are presented in Table 3.
Percentage of weight loss based on randomized group assignment (n = 191).
At baseline, 184 subjects provided valid oxygen consumption data, which allowed for the change in oxygen consumption to be analyzed. There was a significant increase in fitness of 13.4% (15.9%) (2.5 [3.0] mL/kg/min) (P < .001) from baseline to 6 months and a 13.9% (18.3%) increase in fitness (2.5 [3.4] mL/kg/min) from baseline to 24 months. There was no significant group effect or group × time interaction for fitness expressed as milliliters per kilogram per minute or liters per minute (Table 3).
There was a significant group × time interaction between the weight loss categories for weight change measured at 6 and 24 months' follow-up (P < .001) (Table 4). Weight change from baseline to 24 months was 3.0 (2.6) kg (3.5% [3.1%] of initial body weight) for the less than 0% category, −2.2 (1.3) kg (−2.5% [1.3%]) for the 0% to 4.9% category, −6.4 (1.3) kg (−7.4% [1.3%]) for the 5.0% to 9.9% category, and −14.2 (5.2) kg (−16.8% [6.2%]) for the 10% or more category. Percentage weight loss by varying levels of physical activity (minutes per week and kilocalories per week) are presented in Figure 3 and Figure 4. Anthropometric data are presented in Table 5.
Percentage weight loss by physical activity categories (minutes per week) (n = 170).
Percentage weight loss by physical activity categories (kilocalories per week) (n = 170).
Attendance at intervention sessions did not differ between the groups. Completion of telephone calls was significantly higher for the 10% or more weight loss category (81.5% [17.0%] of calls completed) compared with the less than 0% (66.8% [18.8%]) and 0% to 4.9% (68.8% [13.9%]) weight loss categories (P < .05) but not significantly different than the 5.0% to 9.9% weight loss category (75.9% [13.0%]).
The LTPA increased from baseline to 24 months by 1515 (1357) kcal/wk in the 10% or more weight loss category compared with 480 (779) kcal/wk in the less than 0% category, 494 (1377) kcal/wk in the 0% to 4.9% category, and 668 (1146) kcal/wk in the 5% to 9.9% category (group × time interaction, P ≤ .001) (Table 4 and Figure 5).
A, Physical activity at baseline and at 6 and 24 months' follow-up for categories of 24-month weight loss (n = 170); B, physical activity at baseline and at 6, 12, 18, and 24 months' follow-up for categories of 24-month weight loss (n = 81).
There was a significant group × time interaction (P < .001) for change in oxygen consumption (milliliters per kilogram per minute) attained at 85% of age-predicted maximal heart rate among the weight loss categories (Table 4) (n = 165). Compared with baseline, the 24-month increase in oxygen consumption was 5.6 (3.6) mL/kg/min, 2.9 (2.3) mL/kg/min, 1.7 (2.8) mL/kg/min, and 1.1 (2.9) mL/kg/min in the 10% or more, 5% to 9.9%, and 0% to 4.9%, and less than 0% weight change categories, respectively. There was a significant increase in fitness when expressed in liters per minute, with no significant difference between groups based on weight loss achieved at 24 months (Table 5).
There was no significant difference among weight loss categories for the pattern of change in energy intake as determined by a nonsignificant group × time interaction (P = .93). There was a significant group × time interaction for change in weight loss eating behaviors measured by the Eating Behavior Inventory (P = .002) (Table 4). All groups improved in eating behavior from baseline to 6 months' follow-up. However, scores at 24 months were 85.6 (11.7) in the 10% or more category, 80.2 (9.8) in the 5% to 9.9% category, 73.8 (11.7) in the 0% to 4.9% category, and 74.4 (12.1) in the less than 0% category.
Exercise is an important component of weight loss interventions.5,14 However, few studies examining the specific amount and intensity of exercise that may be required to enhance long-term weight loss and that exceed 6 to 12 months have been conducted. Previous results from this study reported that weight loss at 12 months was approximately 10% of initial body weight in response to energy restriction combined with a prescription of a high dose of exercise (approximately 2000 kcal/wk), whereas an approximate loss of 8% of initial body weight was observed in response to energy restriction combined with a prescription of a moderate dose of exercise (approximately 1000 kcal/wk); however, these differences were not statistically significant.6 Prescribed intensity of exercise (moderate vs vigorous) did not influence weight loss outcomes, but this may have been a result of lack of adherence to the prescribed intensity during this study. Unfortunately, our results show that this level of weight loss was not maintained, with a mean weight loss of 5% of initial body weight sustained at 24 months' follow-up regardless of prescribed amount or intensity of exercise (Figure 2).
Weight regain in this study was approximately 50% of the weight lost that was achieved following the initial 6 months of the intervention. This approximates the weight regain previously reported in the literature. Wing4 concluded that weight regain was approximately 43% across a 40-month period following initial weight loss, and similar results have been reported by Perri and Corsica.3
Analysis based on randomized group assignment did not indicate a favorable contribution of exercise to weight loss maintenance. The LTPA increased by 1235 kcal/wk from baseline to 6 months' follow-up; however, only a 720 kcal/wk increase above baseline was sustained at 24 months (Table 2). Moreover, the randomized groups did not sustain the prescribed differences in LTPA, which may have contributed to the nonsignificant differences in weight loss among these groups. Studies of a similar duration have shown comparable results, with physical activity initially increasing before gradually decreasing over time.7,21 Thus, the inability to sustain weight loss appears to mirror the inability to sustain physical activity.
When subjects were categorized based on the magnitude of weight loss achieved at 24 months, the importance of physical activity in sustaining weight loss became more apparent. Individuals achieving and maintaining a weight loss of 10% or more of their initial body weight reported participating in approximately 1800 kcal/wk of LTPA at 6 and 24 months (Figures 3-5). This is approximately 1500 kcal/wk, which corresponds to a mean (SD) of 275 (254) min/wk (55 min/d for 5 d/wk), above the baseline level of LTPA. This level of physical activity is consistent with our previous findings6,7 and confirms the levels of physical activity that should be targeted for successful weight loss.11,12,14,15 The 338 min/wk reported at 24 months approximates 68 min/d for 5 d/wk. This would suggest that the level of physical activity that may be necessary to sustain weight loss for as long as 24 months is approximately twice the public health recommendation for physical activity.10,22 This appears to be consistent with the amount of energy expenditure reported by Schoeller et al9 and that is recommended in the US Dietary Guidelines for prevention of weight regain.11 However, it is important to highlight that this is approximately 1500 kcal/wk, or 275 min/wk, above baseline activity levels for relatively sedentary overweight adults.
Of 191 subjects, 47 (24.6%) were able to sustain a weight loss of 10% or more of their initial body weight at 24 months' follow-up. In addition to sustaining relatively high levels of LTPA, individuals sustaining 10% or more weight loss at 24 months completed more telephone calls with the intervention team during months 6 through 24 (81.5% of contacts completed) compared with individuals achieving a weight loss of 5% or less of their initial body weight at 24 months (<69% of contacts completed). The ability to sustain a higher level of contact may have contributed to the higher level of LPTA and greater engagement in eating behaviors consistent with weight control reported by these participants (Table 4). Perri and Corsica3 have recommended that weight loss interventions follow a chronic care model that sustains contact between the interventionists and participants. The results from this study support this recommendation; however, this contact may not need to be in person. Wing et al23 reported that delivering an 18-month weight loss maintenance intervention in person or via the Internet significantly reduced the proportion of participants gaining 2.3 kg or more. Marcus et al24 reported that non–in person contact (ie, Internet or print) can be effective at increasing physical activity in sedentary adults.
Compliance with dietary recommendations may also have contributed to improved weight loss at 24 months. Individuals sustaining weight loss of 10% or more of their initial body weight at 24 months reported engaging in more weight loss eating behaviors, as measured by the Eating Behavior Inventory, and lower intake of dietary fat compared with individuals sustaining lower levels of weight loss (Table 4). The failure to detect a difference in total energy intake between those individuals sustaining and not sustaining a weight loss of 10% of their initial body weight at 24 months may be a result of the limitations of using a food frequency questionnaire. Howard et al25 reported that compliance with dietary guidelines facilitated the maintenance of a 2.2 kg weight loss over a period of 7½ years, supporting the importance of also targeting this aspect of energy balance. However, the greater magnitude of weight loss achieved in the present study may be a result of a greater emphasis on reduction in energy intake along with the inclusion of physical activity, both of which were not included in the study conducted by Howard et al.
A potential limitation is that the amount of physical activity was based on self report and not objective techniques, which may partially explain the high variability in physical activity reported in this study. Thus, objective assessment of physical activity should be included in future studies that examine this important research question. Moreover, this study did not include a diet-only comparison, which prohibits the ability to examine the additive effect of different doses of physical activity above what can be achieved with diet alone. However, this study tested an intervention approach that is recommended by the National Institutes of Health5 and the 2005 US Dietary Guidelines,11 which includes a combination of changes in both eating and physical activity behaviors to reduce body weight. The results of this study are clinically relevant and provide guidance to health care professionals regarding the magnitude of physical activity that needs to be included in behavioral interventions for weight loss and weight loss maintenance.
An intensive intervention was implemented that required regular contact in person or on the telephone for 24 months. Although higher amounts of contact were predictive of long-term weight loss, this amount of contact may not translate to what is permissible in clinical and community interventions. The optimal frequency of contact that can reasonably be provided in these settings to enhance weight loss outcomes needs to be addressed, and this may involve the integration of alternative modes of contact.
This study demonstrates the difficulty in sustaining weight loss of 10% or more of initial body weight, with approximately 30% of individuals in this study meeting this criterion at 24 months. However, relatively high levels of physical activity appear to contribute to sustained weight loss. In excess of 1800 kcal/wk of LTPA, which is 1500 kcal/wk (275 min/wk) above the baseline level for sedentary individuals, appears to be important for sustaining weight loss of 10% or more of initial body weight. This clarifies the amount of physical activity that should be targeted for achieving and sustaining this magnitude of weight loss, but also demonstrates the difficulty of sustaining this level of physical activity. Research is needed to improve long-term compliance with this targeted level of physical activity. Moreover, continued contact with the intervention staff and the ability to sustain recommended eating behaviors also may be important contributing factors to maintaining significant weight loss that exceeds 10% of initial body weight, which suggests that physical activity does not function independently of these other behaviors.
Correspondence: John M. Jakicic, PhD, Physical Activity and Weight Management Research Center, University of Pittsburgh, 140 Trees Hall, Pittsburgh, PA 15261 (firstname.lastname@example.org).
Accepted for Publication: December 24, 2007.
Author Contributions: Drs Jakicic and Marcus had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: Jakicic, Marcus, and Lang. Acquisition of data: Jakicic. Analysis and interpretation of data: Jakicic, Marcus, and Janney. Drafting of the manuscript: Jakicic and Janney. Critical revision of themanuscript for important intellectual content: Marcus and Lang. Statistical analysis: Jakicic, Lang, and Janney. Obtained funding: Jakicic and Marcus. Administrative, technical, and material support: Jakicic and Marcus. Study supervision: Jakicic.
Financial Disclosure: Dr Jakicic is on the Scientific Advisory Board for BodyMedia Inc and the Calorie Control Council (www.caloriescount.com).
Funding/Support: This study was supported by grant HL64991 from the National Institutes of Health and the National Heart, Lung, and Blood Institute.
Additional Contributions: The staff of the Weight Control and Diabetes Research Center and the Centers for Behavioral and Preventive Medicine at The Miriam Hospital and the Physical Activity and Weight Management Research Center at the University of Pittsburgh assisted with the intervention, data management, and statistical analysis of this study.
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The Rational Clinical Examination
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