1R01DK100345-01A1: An Innovative, Physical Activity-focused Approach to Weight Loss Maintenance
Phase: NA
Conditions: Obesity, Weight Loss, Overweight
Sponsor: Drexel University

Official Title of the study: Project Impact: An Innovative Approach to Weight Loss Maintenance   
NCT number: NCT02363010  
Date of the document: August 1, 2020 
 
 

 
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Design and Randomization  
This study was a three-arm, randomized controlled trial. The study was approved and 
monitored by the Drexel University institutional review board and preregistered at 
clinicaltrials.gov (Clinical Trials Identifier: NCT02363010). Participants provided informed 
consent during enrollment, which was conducted by the research coordinator and research 
assistants. The statistician conducted randomization using a random numbers table. Participants, 
counselors, and other study staff were blind to allocation, with no access to allocation data 
during Phase I. During Phase II, three different forms of behavioral treatment were tested and 
only outcomes assessors remained blinded to condition. An independent officer completed data 
and safety monitoring. 
Participants 
Participants were recruited from the community for this study from 2014 to 2016. 
Inclusion criteria were: BMI 27 – 45 kg/m2 (measured in clinic), age 18-70 years, and 
completion of all steps in the enrollment process. Exclusion criteria were: medical or psychiatric 
conditions that could pose a risk during lifestyle modification or significantly limit the ability to 
begin a program of PA; history of bariatric surgery; current use of weight-affecting medication; 
weight loss of 5% or more in the past 6 months; current pregnancy, lactation, or plans to become 
pregnant during the study period; participation in or plan to participate in another weight loss 
program during the study period; having an immediate family member or household member 
participating in the study. Participants received compensation for assessment visits as follows: 
$25 for baseline, $25 for month 6, $25 for month 12, and $50 for month 18. 
During project planning, estimates of the necessary sample size varied from 300 to 350, 
depending on attrition. At project launch, a final sample of 320 participants was selected, with 

 
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the assumption of up to 30% attrition, to provide 81% power to detect a medium effect size of 
weight loss or MVPA. Power analyses accounted for a three-level hierarchical structure, with 
repeated measures for each participant in a group within one of the three intervention arms, 
assuming a within-subject correlation of 0.5 and a within-group correlation of 0.05 (estimated 
from pilot data). A medium effect size was chosen because 1) an effect of that size may be 
needed to justify a departure from standard behavioral treatment (McGough & Faraone, 2009), 
2) previous research comparing ABT to BT has observed a medium effect size for a primary 
outcome (Forman et al., 2016), and 3) medium or larger effect sizes have been observed for the 
comparison of weight loss in those engaging in high versus low MVPA (Tate, Jeffery, 
Sherwood, & Wing, 2007). 
Shared Intervention Components 
Phase I (Months 1 to 6) consisted of 16 closed-group sessions, held on a weekly (8 
sessions) and then bi-weekly (8 sessions) basis, with approximately 12 participants in each 
group. During Phase I, all participants received BWL treatment designed to induce 10% weight 
loss, with materials adapted from Look AHEAD (2006) and the Diabetes Prevention Program 
(2002). Participants were instructed to keep daily records of dietary intake. Calorie intake was 
emphasized as the key determinant of weight loss. Stimulus control, problem solving, goal 
setting, and social support skills were taught. Participants were instructed to gradually self-
monitor and increase free-living MVPA, with a goal of maintaining 250 minutes per week of 
MVPA by 6 months and beyond. Participants were instructed to conduct MVPA in bouts of 10 
minutes or more. Participants self-reported weekly MVPA minutes and average calorie intake 
during each session’s group check-in, and counselors also provided brief written feedback on 
self-monitoring records on which exercise and dietary intake were reported. Counselors had 

 
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doctoral-level psychology training. In Phase I and II, all group sessions began with private 
measurement of weight. 
Phase II Interventions (Months 7-18) 
 
Group sessions (14 total) continued in Phase II, beginning with 7 weekly sessions 
followed by 4 bi-weekly sessions. The final three sessions were held in Months 12, 15, and 18. 
Each participant also had a 15-minute phone call with a counselor between the quarterly sessions 
(three calls total) to promote continued engagement. Supplementary Table A details the 
intervention content in each arm. 
Behavioral Therapy (BT)  
The BT condition in Phase II continued to be based on Look AHEAD (2006) and 
Diabetes Prevention Program (2002) materials. Sessions were designed to apply traditional 
behavioral skills such as problem solving and goal setting to the challenges of long-term lifestyle 
modification. Approximately two-thirds of intervention content and session time was designed to 
be applied to eating behavior, with a secondary emphasis on PA.  
Behavioral Therapy with Physical Activity Emphasis (BT+PA) 
In the BT+PA condition, approximately two-thirds of session time and content was 
designed to focus on PA, with one-third of session time focused on eating behavior. The 
intervention was created by adapting material from the Look AHEAD (2006) and Diabetes 
Prevention Program (2002) protocols to be PA-focused, and by incorporating techniques from 
Michie’s behavior change taxonomy (Michie et al., 2011). For example, when a session on 
“maintaining motivation” was conducted, exercises and discussion in session were focused 
primarily on enhancing motivation for PA. As another example, the application of goal setting 
skills was primarily focused on PA goals. Progress towards PA goals, particularly the barriers or 

 
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facilitators of such progress, was reviewed in each session in greater detail than occurred in the 
BT condition. PA, rather than eating behavior, was the primary target for problem solving skills. 
Group leaders frequently encouraged development of implementation intentions for PA.  
Acceptance-Based Behavioral Therapy with Physical Activity Emphasis (ABT+PA) 
The amount of emphasis on promoting PA was designed to be similar in BT+PA and 
ABT+PA. However, in ABT+PA, acceptance-based behavioral skills were taught, rather than 
traditional behavioral skills. This approach was adapted primarily from an acceptance-based 
weight loss protocol (Forman & Butryn, 2016). A key goal was to increase awareness of internal 
experiences that shape PA behaviors. The approach validated the sense that many aspects of PA 
are “uncomfortable,” meaning that it can be difficult to tolerate the thoughts (e.g., “I would 
rather be doing something else”), emotions (e.g., boredom), urges (e.g., to avoid or end exercise), 
or physical sensations (e.g., sweating) that occur while one attempts to engage in PA or while 
making PA-related decisions. Participants learned how to respond to internal experiences with a 
stance of non-judgmental acceptance, which enables flexibility (i.e., the ability to engage in a 
wide range of behaviors, regardless of the accompanying internal experiences). Ultimately, 
acceptance was intended to promote long-term persistence in PA. Values clarity, which is 
integral to the use of acceptance skills, included the ability to consider the ways in which being 
physically active enables pursuit of what is most important in one’s life (e.g., being physical fit 
can make travel or community service more feasible). Participants were encouraged to use their 
“long-term mind” to have a heightened awareness of their values at moments of PA-related 
decision making, rather than being driven by transient internal experiences.  
Measures 
Assessments were conducted at Months 0, 6, 12, and 18.   

 
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Demographics. Race, ethnicity, sex, age, and education were self-reported at baseline.  
Moderate-to-Vigorous Physical Activity. Participants were instructed to wear ActiGraph 
(Pensacola, FL) GT3X tri-axial, solid state accelerometers for all waking hours for 7 consecutive 
days at each assessment point. ActiLife software was used with cutpoints defined by Troiano et 
al. (2008) to identify bouts of 10 minutes or more in which PA of moderate-to-vigorous intensity 
was detected. Data were considered valid and included in data analyses if the participant wore 
the accelerometer for at least 10 hours each day for 4 or more days. 
Weight and Height. Participants’ weights were measured by research staff with a 
Tanita® model WB-3000 digital scale, with participants wearing light street clothing. Height 
was measured with a stadiometer. Measurements were taken two times and averaged. 
Half-Mile Walk Time. After a 30 second warm up period, participants were asked to 
walk 0.5 miles on a treadmill in the lab.  Participants were shown how to adjust the speed of the 
treadmill and were instructed to walk as briskly as they could, adjusting the speed as they wished 
throughout the task. Participants were told that the task was a measure of physical fitness.  
Shorter times indicated a greater level of cardiorespiratory fitness (Mayorga-Vega, Bocanegra-
Parrilla, Ornelas, & Viciana, 2016).  
Waist Circumference. Waist circumference was measured horizontally at the umbilicus. 
Measurements were taken two times and averaged if the measurements were discrepant by less 
than 2.0 cm (measurements were re-taken if the discrepancy was greater).   
Treatment Fidelity. All treatment sessions were audio-recorded, and 10% of recordings 
were rated for counselor fidelity to the treatment manual. The treatment manual was organized 
so that each session included a check-in, two or three topics of discussion or activities designed 
to build a particular behavior skill, and assignment of skill builders. Each of these sections of the 

 
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session was rated on a 1-10 scale for adherence, with adherence defined as the extent to which 
the material was delivered as specified in the manual, including pacing of each topic. BT 
sessions also were given a rating for the extent to which the counselor avoiding PA 
contamination (i.e., limited the focus on PA to that specified in the manual) and BT and BT+PA 
conditions were rated for avoiding ABT contamination.  
Data Analysis Plan: Results Through 18 Months 
Data were analyzed in R (Team, 2013) and SPSS Version 25 (IBM Corp., 2017). Data 
distributions and assumptions were examined before conducting any formal statistical test. 
Analyses were conducted on an intent-to-treat basis with multiple imputation via the mice 
package in R (van Buuren, 2011), such that all participants enrolled in the trial were included in 
analyses (BT: n = 110, BT-PA: n = 105, ABT-PA: n = 105), with two exceptions noted for 
exploratory analyses. We performed the analyses for each of the imputed datasets separately, and 
combined the test statistics across datasets based on Rubin’s rule as implemented in the miceadds 
package in R (Robitzsch, 2017). To account for the zero-inflated distribution of MVPA, 
compound Poisson linear regression models (cplm; Zhang, 2013) were used to test the treatment 
effect on MVPA at 12 and 18 months separately, controlling for MVPA measured at earlier time 
points. The effect of treatment on percent weight loss at 12 and 18 months were examined 
separately using general linear models controlling for weight measured at earlier time points. 
General linear models also were used to examine the treatment effect on half-mile walk time and 
waist circumference. Moderation analyses were used to examine whether the effect of treatment 
condition on MVPA or percent weight loss depended on sex, baseline BMI, baseline MVPA, 
weight loss in Phase I or change in MVPA during Phase I. Additional exploratory analyses using 
general linear models were performed to further understand the relationship between specific 

 
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levels of MVPA (regardless of condition) and weight loss outcomes among participants (n = 
271) who provided data at 6 months; this subsample was chosen to reduce missing data to allow 
for greater precision in estimating dose-response for this analysis.