A Micro-randomized Trial of JITAI Messaging to Improve Adherence to Multiple Weight Loss Behaviors in Young Adults
Phase: NA
Conditions: Obesity, Overweight, Overweight and Obesity
Sponsor: University of North Carolina, Chapel Hill

Complete Title: A Micro-randomized Trial of JITAI Messaging to Improve Adherence to Multiple 
Weight Loss Behaviors in Young Adults  
Sponsor: University of North Carolina, Chapel Hill 
NCT number: NCT05625061 
Protocol Date: 12 December 2023 
 
 
University of North Carolina, Chapel Hill 
 
Study Principal Investigator: Carmina Valle, PhD 
Campus Box 7461 
Chapel Hill, NC 27599-7461 
919-843-6886 
email: cvalle@email.unc.edu 
 
PROTOCOL TITLE:  
A Micro-randomized Trial of JITAI Messaging to Improve Adherence to Multiple Weight Loss 
Behaviors in Young Adults 
 
Protocol Version: 1.1  
Version Date: 12/12/2023 
 
I confirm that I have read this protocol and understand it. 
Principal Investigator Signature:   
 
 
 
 
 

 
Table of Contents 
 
ABBREVIATIONS AND DEFINITIONS OF TERMS ....................................................................................................................................... 2 
PROTOCOL SYNOPSIS ................................................................................................................................................................................... 3 
BACKGROUND AND RATIONALE ................................................................................................................................................................... 7 
1. STUDY OBJECTIVES .............................................................................................................................................................................. 8 
2. INVESTIGATIONAL PLAN ...................................................................................................................................................................... 9 
3. STUDY PROCEDURES ........................................................................................................................................................................ 10 
4. STATISTICAL CONSIDERATIONS ....................................................................................................................................................... 12 
5. SAFETY MANAGEMENT ...................................................................................................................................................................... 13 
6. DATA COLLECTION AND MANAGEMENT ......................................................................................................................................... 15 
7. RECRUITMENT, CONSENT, AND RETENTION STRATEGY ............................................................................................................... 16 
8. PLANS FOR PUBLICATION ................................................................................................................................................................. 17 
9. REFERENCES ...................................................................................................................................................................................... 17 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
ABBREVIATIONS AND DEFINITIONS OF TERMS 
 

Abbreviation 
Definition 
AM 
Active Minutes 
API 
Application Program Interface  
ASA-24 
Automated Self-Administered 24-hour Recall 
BCT 
Behavior Change Technique 
BMI 
Body Mass Index 
CES-D 
Center for Epidemiological Studies Depression Scale  
DSMB 
Data Safety Monitoring Board  
EARLY 
Early Adult Reduction of weight through LifestYle intervention  
FAQs 
Frequently Asked Questions 
INCOM 
Iowa-Netherlands Comparison Orientation Measure 
IRB 
Institutional Review Board 
JITAI 
Just-in-Time Adaptive Intervention 
JIT 
Just-in-Time 
MAR 
Missing At Random 
MOST 
Multiphase Optimization Strategy 
MRT 
Micro-randomized Trial 
MVPA 
Moderate to Vigorous Physical Activity 
NCI 
National Cancer Institute 
NHLBI 
National Heart, Lung, and Blood Institute 
NIH 
National Institutes of Health 
OCT 
Office of Clinical Trials  
PAR-Q 
Physical Activity Readiness Questionnaire  
PAQ 
Paffenbarger Physical Activity Questionnaire  
PRS 
Protocol Registration and Results System 
PSS 
Perceived Stress Scale 
QEWP-5 
Questionnaire on Eating and Weight Loss Patterns 
REDCap 
Research Electronic Data Capture  
RCT 
Randomized Clinical Trial 
RF 
Red Food 
SD 
Standard Deviation 
SNAP 
Studies of Novel Approaches to Prevention 
SSRIs 
Selective Serotonin Reuptake Inhibitors 
TFEQ 
Three Factor Eating Questionnaire 
TraCS 
North Carolina Translational and Clinical Sciences  
UNC 
University of North Carolina at Chapel Hill 
WEL-Q 
Weight Efficacy Lifestyle Questionnaire 
WCSS 
Weight Control Strategies Scale 
YA 
Young Adult 
 
PROTOCOL SYNOPSIS 
 
Study Title 
A Micro-randomized Trial of JITAI Messaging to Improve Adherence to Multiple 
Weight Loss Behaviors in Young Adults 
 
Funder 
National Heart, Lung, and Blood Institute (NHLBI) 
Clinical Phase 
NA 

Study Rationale 
An estimated 1 in 2 US adults will have obesity by 2030, which is a major cause 
of morbidity and mortality. The highest risk of weight gain is among young adults 
ages 18-35 years. In-person behavioral interventions generally produce 
clinically significant weight losses, but cost and reduced reach limit their ability 
to impact obesity at a population level. Web-based interventions that mimic the 
structure of weekly face-to-face treatment have proven a viable alternative, 
though weight losses are generally smaller than in-person treatment. Mobile 
treatments have the potential for high reach, but have been less effective, 
producing 1-3 kgs over 6 months. Newer digital intervention approaches called 
“just-in-time adaptive interventions” (JITAIs) promise to improve upon mobile 
outcomes by offering adaptive, personalized feedback on behavior, which 
consists of providing the “right type of support” at “the right time” rather than 
on a fixed schedule. This “just-intime,” or JIT, approach is made possible by the 
emergence of low-cost and widely available digital health tools that allow for 
the collection of continually updated health data. However, to date, no JITAIs 
have successfully targeted multiple weight-related behaviors (weighing, 
activity, and diet), and there has been no systematic examination of what types 
of messaging interventions best promote adherence to these three weight loss 
behaviors, for whom they are effective, and under what conditions. To address 
this problem, we will use a micro-randomized trial to evaluate the effects of 7 
types of intervention messages delivering specific behavior change techniques 
(i.e., BCT messages) in JIT moments on daily achievement of behavioral goals 
among n=201 young adults with overweight and obesity. Findings will guide how 
adaptive, behaviorally- and contextually-dependent messages are incorporated 
into future JITAIs for weight loss.   
Study Objective(s) 
• 
Evaluate the effects of each behavior change technique message (i.e., BCT 
message) on daily adherence to weight loss behaviors in a 6-month micro-
randomized trial among young adults. 
• 
Determine whether the effects of BCT messages on proximal outcomes 
change over time. 
• 
Assess whether the effects of BCT messages on proximal outcomes are 
moderated by participants’ contextual factors. 
Test Article(s) 
(If Applicable) 
All participants will receive a core 6-month weight loss intervention that 
includes evidence-based lessons, behavioral skills training, and daily self-
monitoring of weight, dietary intake, and physical activity. 
Study Design 
 
The Nudge trial applies the Multiphase Optimization STrategy (MOST) 
framework and uses a microrandomized trial design to test the effects of 7 
types of behavior change technique (BCT) messages on achievement of daily 
weight-related goals among 201 young adults. All participants will receive a 6-
month behavioral weight loss intervention using our Nudge mobile app, which 
includes evidence-based weekly lessons, tailored feedback, self-monitoring, 
and daily BCT messages. Participants will receive a wireless scale, activity 
tracker, and track “red” foods (high-calorie foods) in the app and have 3 goals: 
weigh daily, a daily active minutes goal that gradually increases if met, and a 
daily red foods limit. At 3 decision points per day, participants will be 
microrandomized to receive or not receive 1 of 7 types of BCT messages. The 
outcome to be tested is the effect of BCT messages on achievement of same-
day goal achievement (weighing, active minutes goal, red food limit). 
Assessments of the primary outcomes will occur daily, with assessments of 
secondary outcomes at 0, 3 and 6 months. 

Subject Population 
 
Inclusion Criteria 
1. Age 18-39 
2. Body mass index (BMI) of 25-45 kg/m2 
3. English speaking and writing 
4. Own a smartphone with a data and text messaging plan 
Exclusion Criteria 
1. Type 1 diabetes or currently receiving medical treatment for Type 2 
diabetes  
2. Report a heart condition, chest pain during periods of activity or rest, or 
loss of consciousness on the Physical Activity Readiness Questionnaire 
(PAR-Q; items 1-4)  
3. Other health problems which may influence the ability to walk for 
physical activity or be associated with unintentional weight change, 
including cancer treatment within the past 5 years or tuberculosis  
4. Lost 10lbs. or more of body weight (and kept it off) in the last 6 months  
5. Past diagnosis of or receiving treatment for a clinically diagnosed eating 
disorder (anorexia nervosa or bulimia nervosa)  
6. Current symptoms of alcohol or substance dependence  
7. Currently pregnant, pregnant within the past 6 months, or planning to 
become pregnant within the next 6 months  
8. Untreated thyroid disease or any changes (type or dose) in thyroid 
medication in last 6 months  
9. Hospitalization for depression or other psychiatric disorder within the 
past 12 months  
10. History of psychotic disorder or bipolar disorder  
11. Currently participating in a weight loss, nutrition, or physical activity 
study or program or other study that would interfere with this study  
12. Currently using prescription medications with known effects on 
appetite or weight (e.g., oral steroids, weight loss medications), with the 
exception of individuals on a stable dose of Selective Serotonin 
Reuptake Inhibitors (SSRIs) for 3 months)  
13. Previous surgical procedure for weight loss or planned weight loss 
surgery in the next year  
14. Another member of the household is a participant or staff member on 
this trial  
15. Reason to suspect that the participant would not adhere to the study 
intervention.  
16. Reside outside of the United States  
17. Have participated in another study conducted by the UNC Weight 
Research Program within the past 12 months 
Number Of Subjects  
 
201 
Study Duration 
Each subject’s participation will last 6 months. 
The entire study is expected to last four years. 
Study Phases 
Screening 
(1) Screening: screening for eligibility and obtaining consent 
(2) Baseline assessment procedures 

Study Treatment 
Follow-Up   
(3) Intervention: study intervention/experimental treatment 
(4) Follow-up assessments at 3 and 6 months after start date  
(5) Post-study interview with subset of participants 
Efficacy Evaluations 
The results of this micro-randomized trial (MRT) will be used to determine 
whether providing intervention messages tailored to recent behavior and 
context in just-in-time conditions, compared to no message, increases same-
day achievement of 3 proximal behavioral weight loss goals (daily weighing, 
daily active minutes, daily red foods). 
Pharmacokinetic Evaluations 
NA 
Safety Evaluations 
All medical events and safety data will be assessed at assessment points or 
when interim events are reported by participants using a standard form used in 
our ongoing NIH funded trials. 
Statistical And Analytic Plan 
The primary outcome analysis will use generalized estimating equations (GEE) 
to evaluate whether any intervention message (versus no message) increases 
achievement of daily behavioral weight loss goals (weighing, active minutes, 
red food intake) among young adults. Additional analyses will use GEE to test 
the effects of receiving a behavior-specific intervention message (i.e., 
messages about weighing, activity, red foods), as well as the unique effect of 
each of the 7 different BCT message types. We will also examine whether the 
effects of BCT messages on daily adherence to weight loss behaviors change 
over time and are moderated by participants’ contextual factors.  
DATA AND SAFETY MONITORING 
PLAN 
Data safety management in this trial is intended to achieve 4 objectives: 1) to 
minimize the occurrence of adverse effects, especially those related to 
intervention; 2) to effectively manage adverse events as they relate to the study; 
3) to identify when the interventions should be suspended because of concerns 
for participant safety; and 4) to determine when interventions may be resumed 
after having been suspended. The Principal Investigator (PI) will have primary 
responsibility for the safety of participants as it relates to the study protocol, 
which has been approved by the UNC IRB prior to study initiation. The PI and 
Safety Officer will review safety reports assembled by the Study Coordinator. In 
addition, the North Carolina Translational and Clinical Sciences (TraCS) 
Institute Data Safety Monitoring Board (DSMB) is responsible for reviewing data 
from clinical trials approved by the UNC Biomedical IRB. Because the risks to 
subjects participating in this study are expected to be low, we do not anticipate 
the need for a formal Data Safety Monitoring Board. The research team will 
provide continuous monitoring of participant safety and periodic reporting to 
the IRB as required, including any Unanticipated Problems/Severe Adverse 
Events that may have occurred during the study. If risk or complexity is 
significant, the UNC Office of Human Research Ethics may require additional 
reporting or alternative data and safety monitoring. Data safety and monitoring 
activities continue until all participants have completed treatment and until all 
participants have been followed to the point at which study related adverse 
events would likely no longer be encountered. 

BACKGROUND AND RATIONALE 
 
 
1.1 
Introduction 
Young adults (18-39) are at higher risk of weight gain compared to other age groups, 1 which increases 
chronic disease risk.2,3 Weight management interventions for young adulthood are critical,4,5 but few have 
been designed specifically addressing the needs, barriers, and preferences of young adults. 
 
1.2 
Name and Description of Investigational Intervention  
A total of 201 young adults with overweight or obesity will participate in a 6-month behavioral weight loss 
program delivered through the Nudge mobile app. The Nudge app integrates data from wireless scales, 
activity trackers, and a food log, and includes evidence-based weekly lessons, tailored feedback, self-
monitoring, and daily behavior change technique (BCT) messages. Participants will work toward 3 daily 
behavioral goals: self-weigh, meet an active minutes goal, and staying within a “red” food limit (high-
calorie foods). Three times per day, participants will be micro-randomized to receive, or not receive, 1 of 7 
types of BCT messages. We will test the effects of BCT messages on daily proximal outcomes: weighing 
(assessed by wireless scale), meeting an active minutes goal (assessed by activity tracker), or staying 
at/under a red food limit (assessed by in-app food log). 
 
1.3 
Relevant Literature and Data 
Mobile technology approaches have the potential to expand the reach and impact of weight loss 
interventions among young adults in the US given the vast majority own smartphones and use is common 
across subgroups of income, race/ethnicity, education, and residential areas. Prior digital obesity 
interventions, with fixed schedules of intervention delivery, regardless of recent behavioral or weight loss 
success, 6 may not adequately meet the needs of young adults, who desire technology-based, lower-
intensity programs.7 Digital tools such as smartphones, smart scales, and sensors enable real-time 
collection of data on individuals’ behaviors and contexts, which can drive highly adaptive, tailored 
messaging that supports adherence to proximal behaviors that mediate weight loss. Just-in-time adaptive 
interventions (JITAIs) are designed to use this digital health data to deliver highly personalized messages 
(the “right” message) when the participant needs it (the “right” time), while limiting burden on the 
participant.8  
Despite the promise of JITAIs as a scalable approach to health promotion, key gaps remain. First, little is 
known about which behavior change techniques (BCTs) are most effective for daily weight loss behaviors, 
when and for whom they work, or under what conditions.9,10 Second, existing JITAIs often target single 
behaviors, are short-term, and focus on feasibility rather than efficacy.11,12 Few have addressed dietary 
behaviors or combined multiple behaviors such as self-weighing, physical activity, and diet.13–15 Our pilot 
study was the first to report on the use of JITAI messaging for promoting adherence to multiple proximal 
behaviors (self-weighing, physical activity, and dietary intake) that mediate weight loss.16 Further, little is 
known about the type of support needed to improve adherence to multiple weight loss behaviors.17 
Overall, evidence is limited on what types of just-in-time supports to provide, for whom, and under what 
conditions.8,18,19  
Microrandomized trials (MRTs) are a newer experimental design that offers promise for identifying effective 
treatment components that can be delivered within JITAIs for weight loss. Using a MRT design as part of the 
optimization phase of the Multiphase Optimization Strategy (MOST), an engineering-inspired framework, 

can efficiently address multiple questions during JITAI development. While meta-analyses show that 
mobile interventions with personal and frequent interactions are associated with greater weight loss 
(Schippers et al., 2017), experimental evidence is lacking on which types of tailored intervention messages 
best promote daily behavior changes. A formal taxonomy of Behavior Change Techniques (BCTs) has 
identified observable and replicable components of interventions designed to bring about change in 
behavior (e.g., feedback, action planning, social comparison, among others.9,20 Secondary analyses and 
other meta-analyses have identified BCTs that are commonly used in weight management interventions for 
young adults,21,22 but systematic evidence on which BCTs are efficacious, for whom, and under what 
conditions is limited.9 There is a critical need to experimentally test BCTs to address these gaps.23,24 MRTs 
can fill these efficacy gaps by repeatedly randomizing individuals to receive or not receive specific BCT 
messages and measuring proximal outcomes, generating data on the most efficacious components for 
proximal behavior change, while also informing optimal timing and individual contexts.8,19,25   
Few MRTs have optimized JITAIs for weight loss,16,26 and most published MRT trials have focused on single 
behaviors such as physical activity,25,27 engagement with apps,28–30 or stress management.31 While MRTs 
excel at testing the effect of delivering a single treatment component and measuring proximal outcomes, 
few have examined daily JITAI messages for the 3 key weight loss behaviors (self-weighing, physical 
activity, dietary intake) or systematically tested individual BCTs. Most MRTs have been short (e.g., 30 days–
8 weeks),27,32–34 and although JITAI messaging for physical activity shows promise over 6 weeks, there is a 
need to identify an optimal package of BCT-based components that promotes adherence to the multiple 
behaviors essential for weight management.   
To address these gaps, we will use an efficient MRT design to test the effect of tailored JITAI messages, 
compared to no message, on same-day adherence to three daily weight-related behaviors. Young adults 
(n=201) with overweight/obesity will be recruited to a 6-month trial that includes 3 microrandomizations 
per day to evaluate whether 7 different intervention components that deliver distinct BCTs (i.e., BCT 
messages) improve adherence to same-day self-weighing, physical activity, and dietary intake goals. This 
trial will identify efficacious BCTs to optimize JITAI messaging that delivers BCT messages at specific times 
and under certain contexts to maximize adherence to multiple weight loss behaviors. Findings will inform 
future JITAIs and scalable public health interventions tailored to individual characteristics, behaviors, and 
contexts. 
 
1. STUDY OBJECTIVES 
 
The objectives of this study are: 
 
Aim 1: Evaluate the effects of each behavior change technique message (i.e., BCT message) on daily 
adherence to weight loss behaviors in a 6-month micro-randomized trial among young adults 
(N=201). We will use an experimental microrandomized design, powered to detect both the effect of any 
BCT message (versus no message), and the unique effects of 7 different BCT messages (versus no 
message), on daily achievement of weight-related behavioral goals (weighing, active minutes, red food 
intake).  
  
Aim 2: Determine whether the effects of BCT messages on proximal outcomes change over time. We 
will evaluate whether the effects of BCT messages (any message  and by type of BCT) on daily achievement 
of weight-related behavioral goals change over time (day in program, time of day), and if so, the nature of 
the change (e.g., when effects disappear).  
  
Aim 3: Assess whether the effects of BCT messages on proximal outcomes are moderated by 
participants’ contextual factors. The primary moderators to be tested are participants’ 7-day history of 

contextual factors at the time of randomization (achievement of weight-related behavioral goals, 
streaks/lapses in self-monitoring, weight change, previous BCT messages received). Exploratory 
moderators include sex, age, and initial BMI status.  
 
Efficacious intervention messages identified in this study will be used to create an optimized JITAI to be 
tested in a subsequent RCT examining weight losses at 6 and 12 months. This trial will expand our 
understanding of what BCT messages are effective, when they are effective, and for whom. Findings will 
guide how adaptive, behaviorally- and contextually-dependent messages are incorporated into future 
JITAIs for weight loss.  
 
2. INVESTIGATIONAL PLAN  
 
Study Design 
2.1 Overview and study design 
 
The Nudge microrandomized trial (MRT) will 
enroll 201 young adults and test whether 
providing daily intervention messages tailored 
to recent behavior and context and targeting 
one of 7 different behavior change techniques 
(BCTs), compared with not providing a 
message, increases subsequent achievement 
of 3 daily weight-related behavioral goals 
(self-weighing, active minutes, red food 
intake). Participants will receive a mobile-
delivered behavioral weight loss program and 
be micro-randomized three times a day over a 
6-month period (i.e., 504 randomizations per 
individual).  
 
2.2 Intervention Overview 
All participants will receive a 6-month core 
intervention adapted from the Diabetes 
Prevention Program specially for young adults 
and to be delivered remotely via an automated program. The program, Nudge, will be delivered through a 
native smartphone app that includes weekly lessons, weekly tailored feedback, a native food log to track 
red foods, visual displays of behavioral progress, and in-app messages. All participants will receive a 
wireless scale and an activity tracker (Fitbit, San Francisco, CA) in the mail followed by an individual 
videochat session with an interventionist. For each of the 24 weeks of the program, at 3 scheduled time 
points per day, participants will be randomized to receive or not receive a BCT message promoting 
achievement of proximal weight management behaviors (weighing, activity, red food intake). Thus, 
participants will receive 0-3 messages per day. The primary outcome is same-day achievement of daily 
goals (weighing, active minutes goal, red food limit), evaluated among observations in which participants 
received a message compared to observations in which the participant did not receive a message.  
 
Questions answered through Nudge MRT 
• Does providing a BCT message increase goal attainment on the same day it is 
delivered? (Aim 1) 
• Do each of the BCT message types have different effects on goal attainment? (Aim 
1) 
• Do BCT messages’ effects change over time? If so, what is the nature of the change 
(i.e., when does the effect disappear)? (Aim 2) 
• Do BCT messages work differently when delivered under different contexts (e.g., 
time in program, time of day, previous dose of BCT messages, recent behaviors)? 
(Aim 3) 
Intervention components to be tested across 3 behaviors: 7 behavior 
change techniques (BCT messages) 
1.4 Action planning 
Message prompts detailed planning of 
performance of behavior via implementation 
intentions 
1.6 Discrepancy between current 
behavior and goal 
Message draws attention to discrepancies 
between a person’s current behavior and 
previously set outcomes goals, behavioral goals, 
or action plans 
2.7 Feedback on outcome of 
behavior 
Message provides feedback on the outcome of 
performance of the behavior (i.e., weight) 
3.1 Social support 
Message advises on or provides social support 
for performance of the behavior 
6.2 Social comparison 
Message draws attention to others’ performance 
to allow comparison with person’s own 
performance 
10.4 Social reward 
Message delivers positive reinforcement, if and 
only if there has been effort and/or progress in 
performing behavior 
15.3 Focus on past success 
Message advises to think about or list previous 
successes in performing the behavior (or parts of 
it) 

Study Population 
Individuals will be eligible if they meet the following criteria: age 18-39; body mass index (BMI) of 25-45 
kg/m2; English-speaking and writing; and own a smartphone with a data and texting plan. Exclusion criteria 
include being currently pregnant, pregnant within the past 6 months, or planning to become pregnant 
within the next 6 months; type 1 diabetes or receiving medical treatment for type 2 diabetes; a heart 
condition, chest pain, or other health problems that influence the ability to follow physical activity 
recommendations; lost 10 pounds or more in the past 6 months; history of weight loss surgery or planned 
weight loss surgery in the next year; currently taking weight loss medications; report a past diagnosis of or 
receiving treatment for an eating disorder; current symptoms of alcohol or substance dependence; 
untreated thyroid disease or any changes (types or dose) in thyroid medication in last 6 months; 
hospitalization for depression or another psychiatric disorder in the past 12 months or history of bipolar or 
other psychotic disorder; another member of the household is a participant or staff member on this trial; 
currently participating in another weight loss, nutrition, or physical activity study or program; reason to 
suspect the participant would not adhere to the study intervention; reside outside of the United states; 
have participated in another study conducted by the UNC Weight Research Program within the past 12 
months. Individuals that reported joint problems, some prescription medications, or current treatment for 
hypertension or hyperlipidemia will be required to obtain written physician consent to participate.   
The trial is registered on clinicaltrials.gov (NCT05625061) and was approved by the Institutional Review 
Board at the University of North Carolina at Chapel Hill on May 13, 2022.  
 
3. STUDY PROCEDURES  
 
Data Collection 
Measures of the primary outcomes (daily weighing and achievement of active minutes goal and red food 
limit) will be collected daily throughout the study via self-monitoring tools (described below). All study 
participants will complete objective weight measurements and self-administered online surveys at 
baseline, 3 months, and 6 months post-intervention. Participants will also complete two dietary recalls at 
baseline and two dietary recalls at 6 months to measure average dietary intake. Participants will receive 
$50, $25, and $75 for completing baseline, 3, and 6-month assessments, respectively. Online surveys will 
include measures of theoretical mediators, other psychosocial constructs, and process measures. We will 
send emails and texts prompting participants to complete assessments, with follow-up emails and phone 
calls to non-respondents, as necessary. Measures and timing are described below. 
 
Measures 
Primary Proximal Outcome Measures (collected daily) 
Intervention messages are intended to promote achievement of 3 daily weight-related behavioral goals: 
weigh daily, meet a daily active minutes (AM) goal, and stay at or under a daily RF limit. Thus, the primary 
outcome is the achievement of behavioral goals on the day of randomization (i.e., until 12:00AM).   
 
Met daily weighing goal. Weighing behavior will be objectively measured daily using a smart scale (Fitbit 
Aria Air, San Francisco, CA) at the participant’s home. Participants will be instructed to weigh themselves 
daily on the scale in light clothing and without shoes. A dichotomous indicator of whether the participant 
weighed will be calculated. 
 
Met daily active minutes (AM) goal. Participants will have a daily AM goal that may change or stay the same 
at the beginning of each program week. Fitbit trackers will be used to collect daily AM data, defined by 

Fitbit as physical activity of at least moderate-to-vigorous intensity that is accumulated in 10-minute 
bouts. We will calculate a dichotomous outcome of whether a participant met their daily AM goal (days 
with no tracker wear are counted as not meeting the goal) on the day of randomization.  
 
Stayed at or under red foods (RF) limit. Participants will have a daily RF limit that is determined by their sex 
and baseline weight. Daily RF intake will be calculated from participants’ recorded RF in the study app. We 
will calculate a dichotomous outcome of whether a participant stayed at or under their RF limit (days 
without complete tracking [defined as tracked RF consumed during dinner plus breakfast or lunch, or if 
they reached or exceeded their RF limit], are counted as not meeting the RF limit). 
 
Secondary Outcome Measures 
 
Weight will be measured at baseline, 3 months, and 6 months at home using the smart scale. Participants 
will be asked to weigh themselves three times in a row, upon waking and before eating, in light clothing, 
without shoes, and the three weights will be averaged and used to calculate absolute weight change and 
percent weight change over time.    
Proportion of days met daily weighing goal will be calculated as the percentage of study days (out of 168) a 
participant weighed. Proportion of daily AM goal met will be calculated as the proportion of daily AM goal 
met each day of the study using activity tracker data. Proportion of daily RF limit will be calculated as the 
percentage of the daily RF limit recorded each day of the study in the study app. The total number of AM 
and the total number of RF on the day of message randomization will be measured for each day of the 
study. Following the day of message randomization, we will measure met daily weighing goal tomorrow, 
met daily AM goal tomorrow, and stayed at or under daily RF limit tomorrow.  
Tertiary / Exploratory Measures  
Behavioral measures  
• 
Self-reported dietary intake will be assessed using the NCIs Automated Self-Administered 24-hour 
Recall (ASA-24; National Cancer Institute) at baseline and 6 months. Participants will complete 
two unannounced self-reported recalls; one weekday and one weekend day.  
• 
Self-reported physical activity at baseline, 3, and 6 months will be assessed with the Paffenbarger 
Physical Activity Questionnaire (PAQ) which assesses leisure-time activity and provides an 
estimate of minutes per week of moderate-to-vigorous intensity, and calories/week of light (5 
kcal/min), medium (7.5 kcal/min), and high (10 kcal/min) intensity activities (Paffenbarger et al., 
1978).  
• 
Sedentary Activity at baseline, 3, and 6 months will be assessed with the Sedentary Behavior 
Questionnaire from the EARLY trials (Rosenberg et al., 2010; Lytle et al., 2014).  
Psychosocial measures  
• 
Self-efficacy for eating, measured using the Weight Efficacy Lifestyle Questionnaire (WEL-Q; 20 
items).35 
• 
Self-efficacy for exercise, measured using the 12-item Self Efficacy and Exercise Habits Survey.36 
• 
Self-regulation for exercise, measured with the 10-item Exercise Goal-Setting Scale and the 10-
item Exercise Planning and Scheduling Scale.37 
• 
Motivation for making changes in diet (15 items) and exercise (15 items), measured using the 
respective Treatment Self-regulation Questionnaires.38 
• 
Perceived competence for diet (4 items) and exercise (4 items).39 
• 
Health-related quality of life, measured using the CDC Healthy Days measure (CDC 1993). 
• 
Depressive symptoms, measured using the Center for Epidemiological Studies Depression Scale 
(CES-D). 40 

• 
Weight control strategies, measured with the Weight Control Strategies Scale (WCSS; 30 items).41 
• 
Hunger, restraint, disinhibition measured using the Three Factor Eating Questionnaire (TFEQ; 51 
items).42 
• 
Perceived stress, measured using the Perceived Stress Scale (PSS; 10 items).43 
• 
Binge eating measured using the revised Questionnaire on Eating and Weight Patterns (QEWP-5.44 
• 
Social comparison orientation measured using the Iowa-Netherlands Comparison Orientation 
Measure (INCOM; 11 items).45 
• 
Weight-related information avoidance (10 items).46 
• 
Relatedness measured with a scale adapted from Basic Need Satisfaction at Work Scale (3 
items).47,48 
• 
Message relevance measured using 2 items from our previous work,49 which was adapted from 
previous studies.50,51  
Other measures  
We will assess several supporting measures, including sociodemographic characteristics, medical events, 
and medication use. Program engagement (app views, lessons accessed, feedback messages viewed, 
goals set or modified), process, and adherence measures (self-weighing, activity tracking, red food 
tracking, daily goal achievement) will be collected throughout the study period and used to calculate 
behavioral adherence in the prior 7 days and streaks and lapses in goal achievement. Program 
acceptability and satisfaction will be assessed using post-intervention program evaluation questions and 
in post-intervention semi-structured interviews after 6 months. 
 
4. STATISTICAL CONSIDERATIONS 
 
 
Sample Size and Power  
Our power analysis is based on a sample size calculator built in an R package (MRT-SS)52 for detecting 
proximal treatment effects in microrandomized trials developed by Liao et al,53 expanding on more general 
results for sample size calculations for longitudinal trials from Tu et al.54 Inputs to the sample size 
calculator are: desired alpha (.05), the number of outcome occasions (T =168 days for each proximal 
outcome), average probability of message availability each day, the randomization probability for a given 
message if it is available (0.5), and the standardized proximal treatment effect 
across all time 
points. Based on our prior research 16 and the previous MRTs with published effects sizes,31,32,55 we assume 
that 
ranges from .03 to .15. Based on our previous studies with young adults56,57 and the pilot MRT,16  
assuming 17% attrition by day 168, we estimated that a sample size of N=201 would be required to have an 
average of 150 usable days per person (168 days*.83 + 84 days*.17 = 154), for a total of 30,954 person-day 
observations (N=201*154; i.e., over 4400 person-day observations per each of 7 BCT message 
interventions across 3 behaviors). This is consistent with a prior MRT that evaluated 6061 available 
decision points to test 2 different options for an intervention component  (i.e., walking suggestions, anti-
sedentary suggestions) among 37 participants.32 We will use all available data points in these analyses and 
test the sensitivity of our findings to dropout status by conducting completer-only and dropper-only 
analyses. The estimated minimum detectable standardized effect size with 80% power across the planned 
analyses ranges from .04 to .13.  
  
 

 
Statistical Analysis Plan 
Data analysis will be performed using R statistical software (version 4.0.3). Baseline demographic and 
descriptive characteristics will be summarized globally, using frequencies and percentages for categorical 
variables, and means and standard deviations (SD) for inherently quantitative variables. Prior to 
conducting data analyses, we will audit the data for completeness and quality, including missing data. We 
will evaluate response distributions to ensure that they meet assumptions of planned analyses (see 
below), including the detection of outliers.  
Analysis of primary outcomes  
We will test: 1) whether any intervention message (versus no message) increases adherence to daily 
weight loss behaviors among young adults, 2) whether a behavior-specific message (versus not receiving 
the behavior-specific message) increases adherence to the respective behavioral goal, and 3) finally the 
unique effect of each BCT message for the three proximal outcomes. We will use generalized estimating 
equations (GEE) with an independence working residual correlation matrix to account for nesting of 
observations within individuals.58 and use Benjamini-Hochberg-Storey correction for multiple testing.59  
Analysis of whether effects of BCT messages change over time  
We will also examine whether the effects of BCT messages on daily adherence to weight loss behaviors 
change over time (week in program, time of day) and, if so, the nature of the change (e.g., when effects 
disappear). Thus, we will expand upon the model described above by: 1) including linear and quadratic 
main effects of time and interaction terms, between an indicator of day in the program and treatment 
assignment, to test whether the treatment effect changes over time.58 We will examine differences in the 
average and estimated time trends in treatment effects of receiving a behavior-specific message, and then 
the unique effect of each BCT message for the three proximal outcomes.   
Analysis of whether effects of BCT messages are moderated by participants’ contextual factors 
We will evaluate whether the causal effect of receiving a BCT message interacts with participants’ 
contextual factors, including past behaviors and individual characteristics. We will use standard 
moderation analysis within the GEE framework for these analyses, which involves the inclusion of main 
effects and interaction terms. Significant moderation effects will be probed using simple slopes analysis to 
determine the conditional region and direction of significance. The primary moderators to be tested are 
participants’ 7-day history of contextual factors at the time of randomization (achievement of weight-
related behavioral goals, streaks and lapses in self-monitoring, weight change, previous BCT messages 
received). Exploratory time-invariant potential moderators include demographic and health characteristics 
(e.g., sex, age, baseline BMI).   
  
 
5. SAFETY MANAGEMENT  
 
Data safety management in this trial is intended to: 1) minimize the occurrence of adverse effects, 
especially those related to intervention; 2) effectively manage adverse events; 3) identify when the 
interventions should be suspended because of concerns for participant safety; and 4) determine when 
interventions may be resumed after having been suspended. The Principal Investigator (Valle) will have 
primary responsibility for the safety of participants as it relates to the study protocol, which has been 
approved by the UNC IRB prior to study initiation. The PI and Safety Officer will review safety reports 

assembled by the Study Coordinator. In addition, the North Carolina Translational and Clinical Sciences 
(TraCS) Institute Data Safety Monitoring Board (DSMB) is responsible for reviewing data from clinical trials 
approved by the UNC Biomedical IRB. Because the risks to subjects participating in this study are 
expected to be low, there is no formal Data Safety Monitoring Board. The research team will provide 
continuous monitoring of participant safety and periodic reporting to the IRB as required, including any 
Unanticipated Problems/Severe Adverse Events that may have occurred during the study. If risk or 
complexity is significant, the UNC Office of Human Research Ethics may require additional reporting or 
alternative data and safety monitoring. Data safety and monitoring activities continue until all participants 
have completed treatment and until all participants have been followed to the point at which study related 
adverse events would likely no longer be encountered. 
 
Participant Safety 
The risks to human subjects in this study, including psychological and physical risks, are judged to be 
minimal. The anticipated benefits are great, insofar as the results will be used to determine if mobile-
delivered behavior change strategies are effective for obesity risk reduction in a sample of young 
adults. The primary risks, while minor, include: discomfort with being asked about personal information 
related to their diet, physical activity, and weight; risks of increasing physical activity (injuries, blood 
pressure changes, dizziness, fainting, fatigue, and in very rare cases heart attack, stroke, or even death); a 
low risk of extreme dieting and/or extreme psychological reaction to dietary restriction; risk of breach of 
confidentiality via telephone calls, emails, text messages, or the smartphone app. 
 
Adequacy of Protection Against Risks  
a. Informed Consent and Assent  
Recruitment and Informed Consent: The UNC IRB has approved the study protocol and has reviewed and 
approved the informed consent document. Once an individual has been deemed potentially eligible to 
participate through online and telephone screening, study staff will provide more study details and 
describe the concept of random assignment, and assessment procedures over the telephone. Individuals 
who remain interested will receive an email directing them to a unique and secure REDCap link to an 
online informed consent. After clicking on the link, they will be directed through a series of screens that 
present the informed consent document. The online informed consent records will be retained, and 
recruitment of participants will be done by adhering to HIPAA regulations. Accrual reports will list enrolled 
participants and excluded participants throughout the stages of the research. This routine monitoring 
allows for early identification and resolution of potential problems during the recruitment phase. The 
anticipated recruitment duration is 20 months. All key personnel have attended the required courses on 
human subject protection and HIPAA regulations, and certificates of IRB training completion are on file 
with the University of North Carolina.  
b. Protections Against Risk  
Protections against Psychological Risks: Participants are not required to share information in online 
questionnaires and can elect not to share sensitive and confidential information with the study. 
Participants will be encouraged to contact the Principal Investigator if they feel they have incurred any 
emotional distress as a result of study participation. As this is a voluntary study, a participant is free to exit 
at any point if discomfort should occur. Individuals scoring >16 on the Center for Epidemiological Studies 
Depression Scale (CES-D) at baseline, 3- or 6-month assessments (indicating levels of depressive 
symptoms that might benefit from follow up with a health care provider) will be given a letter explaining the 
survey and providing information and referral to resources.  
Protections against Physical Risks: To ensure medical readiness to begin physical activity, participants will 
complete a physical activity readiness questionnaire (PAR-Q). The PAR-Q assesses the following medical 
conditions: heart problems, chest pains, faintness or dizzy spells, high blood pressure, bone or joint 

problems such as arthritis, that have been or could be aggravated by exercise, prescription medication 
use, and other medical reasons why exercise would not be advisable. Participants endorsing yes to any 
items 1-4 on the PAR-Q (experience of heart problems, frequent chest pains, faintness or dizziness, bone 
or joint problems) will be excluded from the study. We also will monitor any major musculoskeletal 
problems that develop during the intervention (e.g. broken bones) using a medical events questionnaire at 
3 and 6 months and will determine whether these appear related to our study. Participants who develop 
musculoskeletal problems or other health problems that may affect safe participation will be instructed to 
stop exercising until the problem resolves and their physician approves resuming physical activity.  
All participants will be advised about safe weight loss practices including dietary change and increasing 
physical activity at their initial study visit. Participants will be advised to gradually increase their physical 
activity and to use walking as a primary form of activity and will be taught that the appropriate rate of 
weight loss is 1 to 2 pounds per week. In addition, we will carefully monitor changes in weight during our 
trial. We will collect information at each assessment timepoint on hospitalizations for any psychiatric 
problem, including depression and eating disorders. We will track weight changes using smart scale 
weights and will identify any individual who loses more than 20% of their body weight, has a BMI ≤ 18.5 
kg/m2 at any point during the program, or loses more than 15 pounds in any month during the trial., We will 
have a telephone call with these participants within 2 weeks, discuss our concerns with them, and make 
referrals if appropriate. If there is no improvement in weight status, the participant will be unable to 
continue to participate in the intervention.  
Protections to Ensure Confidentiality of Participants: All data records related to a participant’s 
involvement in this research study will be stored in encrypted files on servers that adhere to the University 
policy on storage and transmission of sensitive data. Participant identity on these records is indicated by 
an ID number and the information linking these numbers with participant identity will be kept separate 
from the research records. In addition, all research databases will have password-controlled access.  
The Fitbit API will be used to access data from the participant’s scale, activity tracker, and Fitbit app. 
During the consent process, participants will consent for the data from their specific devices to be 
accessed by our study. They will need to enter their Fitbit username and password during the app setup 
process to allow Fitbit data to be sent to our study server. The study smartphone app uses a Standard 
OAuth 2.0 security model for logging in to Fitbit. Fitbit usernames and passwords will not be stored in any 
way with this study. Instead, the weight and tracker data will be connected to participants by their unique 
study ID that they will also enter during the app setup process. Data are transmitted on secure servers that 
adhere to university policy on Sensitive Data. The risk of breach of confidentiality over the Fitbit websites 
will be partly subject to each individual’s comfort in sharing information in their individual profile. To 
further minimize the risk of breach of confidentiality, all participant activities on the Fitbit websites will be 
voluntary. Consent forms will also clearly communicate the risk of this type of disclosure to participants.  
Removal of Patients from Protocol. Participants will be removed from the protocol should they experience 
greater than minimal risk as detailed above. Participants will be reminded that their participation is 
voluntary and that they may withdraw from the study at any time without consequence by contacting the 
Principal Investigator. In addition, we expect that pregnancies will occur. We will stop all intervention 
activities for anyone who becomes pregnant.  
 
 
6. DATA COLLECTION AND MANAGEMENT  
 
Participants will provide physical data (objective weight and self-reported height) and self-reported 
questionnaire data online specifically for research purposes using the REDCap computer-assisted 
program that has built-in validation checks for range, data type, and completeness. All measurements will 
undergo consistency and outlier checks, compared with raw data, and edited as required. REDCap 
includes detailed audit logs that document any database changes, and we will document protocols for 

cleaning data. Identifiable information collected in online surveys will include the participant’s name, 
address, phone numbers, and date of birth. Food log data from the study smartphone application and 
weight and activity data from Fitbit will be transmitted to study servers.  
 
7. RECRUITMENT, CONSENT, AND RETENTION STRATEGY 
 
Recruitment 
Young adults will be recruited using a multi-pronged approach including: 1) postings on social media 
including Facebook and Instagram 2) direct mail to heads of households in select geographic areas; 3) 
emails through listservs comprised of the target audience; 4) advertisements on select media accessed by 
young adults, including television, radio, Spotify; and 5) targeted mailings, emails and advertisements to 
young adult men and minority groups.  
On Meta (Facebook/Instagram), we will purchase advertisements and “Boosted Posts” with recruitment 
information about the study that will link to the recruitment website and online screening survey. The ads 
and posts will be targeted specifically to reach adults between the ages of 18 and 39 that live in the United 
States and can also be targeted specifically to reach subgroups based on sex or race/ethnicity if needed.  
We plan to enroll 10 participants per month over 20 months. Initially, no groups will be excluded or limited 
based on sex, race, and or/ethnicity. However, women are generally over-represented in weight control 
studies; therefore, to be able to test for differences in the treatment effect by sex, we may need to 
specifically target recruitment of men. Our research group has had success in recruiting higher 
percentages of men by using pictures of men in Facebook/social media advertisements, and by using 
terms such as “wellness” and “health” instead of “weight loss.” Therefore, we will use these strategies to 
increase our recruitment of men if we are under our targets. Additionally, to recruit a sample of at least 
30% non-white participants (as outlined in our NIH recruitment plan), we will identify minority groups 
through social media platforms and community groups, and tailored recruitment materials.  
 
All recruitment efforts will direct participants to a study website with a more detailed description of the 
research study and FAQs about participating in research. Interested individuals will click through to a 
REDCap web screening survey to determine initial eligibility. Those who are preliminarily eligible will be 
contacted by trained study staff and will undergo additional phone screening. Eligible and interested 
individuals will receive an email directing them to a unique REDCap link to an online informed consent. 
After providing consent, participants will be instructed on procedures for 1) completing one weekday and 
one weekend self-reported 24-hour dietary recall, 2) completing baseline online questionnaires, and 3) 
completing their baseline weight measurement using a Bluetooth-connected scale. The Fitbit scale and 
activity tracker will be mailed to the participant. After completion of baseline assessments, the participant 
will be scheduled for a one-on-one telephone/videochat session during which they will be informed about 
study procedures, assisted with downloading of the study smartphone app, and questions about getting 
started will be answered.   
 
Retention 
A systematic protocol will be followed to minimize dropouts. At baseline, the names and addresses of 
several friends and family members who can be contacted are obtained for use if we lose touch with the 
participant and need to contact them for study assessment completion. The study provides incentives for 
completing the follow-up assessments to offset any time costs and to promote retention ($50 for 
completing the baseline assessment, $25 for the abbreviated 3-month assessment, and $75 for 
completing the 6-month assessment). For each assessment visit, we will send participants an email that 
will include a link to online questionnaires with an expected completion date as well as a scheduled date 
and time to step on their scale. Participants will be sent email and/or text reminders the day prior to their 

telephone appointment based on their preference. Missed weights and/or calls will be immediately 
followed up by phone and rescheduled.  
We will review participant engagement with the Nudge app weekly and will use structured protocols for 
promoting engagement with the intention of also promoting retention. 
 
8. PLANS FOR PUBLICATION 
 
 
As Principal Investigator of this grant application and clinical trial, Dr. Valle will comply with the clinical 
trial information dissemination expectations of the NIH policy to register and submit summary results at 
ClinicalTrials.gov. Karen Hatley, Project Manager, will be responsible for handling ClinicalTrials.gov 
requirements for this project under the Dr. Tate's oversight. Consistent with the terms and conditions of 
NIH funding, we will ensure the submission and updating of registration and results information for this 
clinical trial in the timeframes established by the Final Rule. Registration and results reporting in 
ClinicalTrials.gov will be completed within the following timeframes:   
• 
Registration of the trial at ClinicalTrials.gov no later than 21 days after enrolling the first participant  
• 
All submitted information will be updated at least once a year.  
• 
Any apparent errors, deficiencies, and/or inconsistencies identified by NIH as part of the quality 
control review process and any other errors identified will be addressed by the responsible party.  
• 
Corrections to submitted information will be made within 15 days for registration information and 25 
days for results information.  
• 
Trial results will be submitted no later than one year after the primary completion date.  
Informed Consent Documents for the clinical trial will include a specific statement relating to posting of 
clinical trial information at ClinicalTrials.gov. The UNC IRB has template language explaining that the study 
will be posted on ClinicalTrials.gov that investigators are required to include in the consent document for 
the trial.,  
As PI, Dr. Valle will work closely with the UNC-CH Office of Clinical Trials (OCT), which serves as the 
university’s internal PRS. The OCT has responsibility for ensuring that clinical trial registration and 
reporting occurs in compliance with NIH policies. The OCT has support staff to facilitate the process of 
registration and results reporting to ClinicalTrials.gov, and our team will work closely with them to register 
this trial and to submit summary results to the website in a timely manner, in keeping within the required 
timeframes. Once data collection is complete, our research team will work to prepare and submit trial 
results no later than one year after the primary completion date.  
 
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