PROJECT SUMMARY/ABSTRACT
One third of US children have overweight or obesity; children are developing obesity at higher rates than at any
other time in human history. Social determinants of health (SDoH) are strong and especially intractable risk
factors for childhood obesity, creating a structural context of stress in early life. Compared to children in high
socioeconomic status (SES) households, children in low SES households have 3-4 times higher odds of obesity
and elevated biomarkers for chronic stress (cortisol) after adjusting for individual level behaviors. Thus, studies
aimed at enhancing resilience to structural SDoH risk factors are critically important for reversing the childhood
obesity epidemic. Situated at the intersection of structural SDoH and individual behavior, outdoor preschools
present an ideal research opportunity for research to build resilience to low family SES for both the prevention
and management of childhood obesity. Rigorous research on this topic is nearly nonexistent, but its plausibility is
supported by mounting evidence that outdoor time may influence biological causes of childhood obesity.
Specifically, imbalance in microorganisms found in the digestive tract, referred to as the gut microbiome, is
associated with childhood obesity. Environmental factors strongly affect gut microbiome diversity, and urban
environments reduce gut microbiome diversity by limiting contact with green spaces and microbe-rich soil. Contact
with nature improves resilience and reduces stress in children; neighborhoods with lower household income often
lack access to parks and green spaces, exacerbating existing inequities. Thus, the gut microbiome, may be an
especially informative marker of the effectiveness of outdoor preschools for enhancing biological resilience to
obesogenic SDoH. No study in any population has longitudinally characterized gut microbiome diversity with
obesity in early childhood, nor has the interaction of stress and gut microbial diversity been evaluated. In this
application, “Childhood Obesity: the role of the gut Microbiome, outdoor Time, and Stress” we will conduct a
longitudinal natural experiment evaluating the impact of a novel outdoor preschool model on gut microbial diversity
and stress biomarkers, and the association with obesity. We will partner with Tiny Trees, an entirely outdoor
preschool in Seattle, WA, and the largest outdoor preschool in the US. Tiny Trees reserves 50% of enrollment
spots for families eligible for free/reduced tuition. We will recruit 300 children 3-5 years of age; 150 attending Tiny
Trees and 150 from the Tiny Trees waitlist attending an indoor preschool that provides tuition assistance to income
eligible families. To maximize sample size and statistical power, we will analyze ~400 stool samples collected using
an identical protocol and population as part of Dr. Fyfe-Johnson’s K01. Our Specific Aims are to: 1) estimate the
effect of an outdoor preschool model on gut microbiome diversity, stress biomarkers, and body mass index,
2) evaluate gut microbiome diversity as a mediator on BMI and SDoH as a potential modifier of effects on
primary outcomes, and 3) conduct cost-benefit and cost-effectiveness analyses of the outdoor preschool model
to assess the return on investment for childhood obesity prevention.