Quantifying the U.S. obesogenic environment and its quasi-causal association with obesity: a cross-sectional twin study

Obesity is a chronic disease that develops via complex interactions between human biology and the obesogenic environment. This study aimed to develop a high-resolution index of combined obesogenic neighborhood exposures in the U.S. and examine its association with body mass index (BMI), independent of familial factors shared by twins (e.g., genetics and early life environment). This cross-sectional study included 11,152 adult twins (66% female, 69% monozygotic [MZ], mean age 42 [SD 18]) from the Washington State Twin Registry. The Obesogenic Built Environment CharacterisTics United States (OBCT-US) index captured neighborhood exposure to the modified retail food environment, walkability, area deprivation, and the normalized difference vegetation index around residential addresses. Univariate twin models estimated the heritability of the OBCT-US-index and BMI. Full-informed maximum likelihood linear regressions were applied to assess associations between the OBCT-US-index and BMI at the individual level among all twins and then pairwise differences within MZ and same-sex dizygotic (ssDZ) twin pairs. BMI showed high heritability (74%), whereas the OBCT-US-index was primarily influenced by unique environmental factors (63%). A 10% higher OBCT-US-index was associated with a 0.16 [95% CI: 0.11, 0.22] kg/m² higher BMI in individuals, but no association remained within MZ twin pairs 0.03 [-0.03, 0.09] or in ssDZ twin pairs -0.02 [-0.15, 0.11]. We conclude that while a more obesogenic environment was associated with higher BMI, this relationship was confounded by familial factors.