Obesity prevalence is projected to exceed 50% of adults by 2030 under current trends. Individual-focused lifestyle interventions can produce weight loss, but outcomes vary between participants. Psychological factors, notably perceived stress, coping ability, and affect, are implicated in behavior change and may influence weight loss success. Daily fluctuations in stress and coping can disrupt physical activity and eating behaviors, limiting weight loss.
Ecological momentary assessment (EMA) offers repeated short assessments via mobile applications to capture antecedents, behaviors, and consequences in naturalistic settings, permitting evaluation of day-level temporality. EMA studies have linked momentary stress and affect with physiological markers such as cortisol and with behavior (for example, physical activity). Using EMA across a weight loss intervention may reveal pathways by which stress and related constructs influence health behaviors, and can support development of adaptive in-the-moment supports (ecological momentary interventions, EMI) if warranted.
The INSTANT study (intensive longitudinal assessment of stress and stress-related behaviors across a behavioral intervention) aims to elucidate pathways between stress-related constructs and subsequent health behaviors during a community-based behavioral weight loss program.
Primary exposure: variability (difference) in signal-contingent survey measures of stress, coping, and affect early in the program.
Primary outcome: weight change over the 6-month program.
Secondary outcomes: device-measured physical activity and sleep.
Hypotheses:
INSTANT is a prospective observational cohort embedded in existing community-based weight management programs. The protocol follows EMA reporting guidelines and received institutional review board approval from the University of Kansas Medical Center in May 2024 (IRB#: 00160436). The study was registered on ClinicalTrials.gov (NCT06668259) in October 2024. The protocol undergoes at least annual IRB review per institutional and federal requirements.
The study targets approximately 50 adults with obesity (BMI ≥ 30 kg/m2) who are newly enrolled in community-based weight management programs in a Midwestern metropolitan area. Eligible participants must be ≥18 years old, own a smartphone, and agree to download the study mobile application to receive EMA prompts. Recruitment will occur at initial program consultation or orientation visits and via flyers provided at those visits. Participation is allowed even if a person discontinues their community program after enrollment; later INSTANT assessments can still be completed.
Community weight management programs involved commonly provide weekly 1-hour video meetings with trained health educators, group peer support, structured low-calorie nutrition plans, personalized activity recommendations, and behavior-change strategies.
Each participant completes four in-person visits timed to the weight loss program: baseline (week-0), early program (6 weeks), mid-point (12 weeks), and program end (26 weeks). At each visit, staff measure height and weight and administer questionnaires assessing chronic stress, coping, affect, food cravings, and other weight-related behaviors. These measures capture between-person differences in chronic stress and related constructs that complement intensive EMA data.
At each measurement wave participants complete at least 14 consecutive days of EMA via a smartphone application. Daily EMA consists of one morning survey, four signal-contingent surveys delivered within fixed 3-hour windows during the day, and one nighttime survey. EMA items assess momentary stress, coping, affect, and contextual behavioral information. The primary exposure metric is early-program signal-contingent variability in stress, coping, and affect derived from EMA responses.
During each 14-day EMA period participants wear devices to collect objective measures of physical activity and sleep. Activity metrics include moderate-to-vigorous physical activity (MVPA) and acceleration-derived ENMO. Participants also collect waking salivary samples for cortisol assay during EMA periods to permit comparison between momentary self-reported stress and physiological stress markers.
Primary outcome: change in body weight across the 6-month behavioral weight loss program, measured at clinic visits.
Secondary outcomes: device-measured physical activity and sleep during EMA periods and across program timepoints. The protocol indicates planned comparisons at initial (12-week) and full (26-week) program milestones.
The protocol frames the primary exposure as variability in early-program EMA measures (stress, coping, affect) and intends to evaluate associations between that variability and weight change over 6 months. Secondary analyses will assess relationships between EMA variability and physical activity and sleep. Exact analytic methods, statistical models, covariates, and power calculations were described in the source protocol; specific numeric details beyond the stated sample target were not reported in the summary available here.
Initial startup for the project began in March 2024. The study received IRB approval in May 2024 and was registered on ClinicalTrials.gov (NCT06668259) in October 2024. Recruitment began in March 2025, and the authors anticipated study completion in early 2027. No datasets have been generated or analyzed to date; all relevant data will be made available upon study completion.
The study aims to determine whether intra-individual variability in daily stress, coping, and affect early in a behavioral weight loss program predicts weight change, physical activity, and sleep. If variability in stress-related constructs is associated with poorer outcomes, these data would support development of adaptive ecological momentary interventions (EMI) to provide in-the-moment strategies (for example, prompting physical activity during low-coping times) to support behavior change and potentially improve weight loss.
Limitations inherent to the protocol include observational design and dependence on participant adherence to EMA, device wear, and saliva collection; the summary does not report analytic results or participant-level findings. The protocol notes that participants who discontinue the community program may continue INSTANT assessments, which may mitigate attrition bias for analyses.
This work was supported by the National Institute of General Medical Sciences (P20GM144269). The funder had no role in study design, data collection and analysis, decision to publish, or manuscript preparation. Data will be shared upon study completion. One author (Dr. Jakicic) serves on the Scientific Advisory Board for Wondr Health, Inc.; no other competing interests were reported.