Poor dietary and physical activity (PA) behaviors escalate risk for obesity, cancer, and other chronic diseases,
and contribute to disparities. Mid-life is a vulnerable life stage when obesity rates peak and chronic diseases
emerge. Neighborhood environments provide opportunities, barriers, and cues/triggers to engage in healthy or
unhealthy behaviors. Overall, however, research findings on environment-behavior associations are
inconsistent and effect sizes are small. This research is limited by sole focus on residential neighborhoods,
failure to consider the environment’s role in within-person daily and momentary differences in behaviors, and
scarce attention to identifying for whom the environment matters and under what conditions. A new approach
is needed that considers the broader environment where people spend time (activity space). Our objective in
the proposed study is to address misspecification of environmental exposures ubiquitous in prior research and
provide a definitive test of activity-space environment explanations for between-and within-person diet and PA
variations during mid-life. The central hypotheses are that activity-space environmental exposures contribute to
both between- and within-person variations in dietary and PA behaviors and more strongly influence these
behaviors than residential-neighborhood environments alone. Drawing on Temporal Self-Regulation Theory,
we also hypothesize activity-space environmental exposures are more consequential for diet and PA when
self-regulatory capacity—trait or state factors that affect a person’s ability to make efforts to regulate
behavior—is diminished. An in-depth, rigorous study of 510 Latinx, African American, and White adults ages
40-64 is proposed. We will use a rich combination of cutting-edge geographically-explicit ecological momentary
assessment (GEMA) methodologies: global positioning system (GPS) location tracking; smartphone-based
mini-surveys of diet, PA, and state factors; and accelerometry, as well as three 24-hour dietary recalls,
anthropometric measurements, and questionnaires of trait and other factors. Sophisticated routine, daily, and
momentary activity-space measures will be derived based on the spatial extent of their movement, but also
duration of exposure. Multiple features of the residential and activity-space environments will be measured
using GIS including absolute and relative availability of healthful and unhealthful foods, walkability, recreational
resource availability (e.g., parks, fitness facilities, greenness), and crime. For the first time, this innovative
research will employ a dynamic environmental exposure approach using GEMA to supply evidence on the
environment’s role in between- and within-person variations in diet and PA during mid-life, a pivotal time, in a
racially/ethnically diverse sample. As such it will contribute to a much-needed shift in how environmental
determinants of behaviors are studied, making a lasting impact on the field. Our research is significant because
the results can inform new targets for lifestyle and place-based interventions to improve health during mid-life
and set the stage for better later-life health.