• Kimon Krenz, Rosemary McEachan, Mikel Subiza-Pérez, Aidan Watmuff, Tiffany Yang, and Laura Vaughan.
• The Bartlett School of Architecture, Faculty of the Built Environment, University College London, London, UK. Electronic address: k.krenz@ucl.ac.uk.
• Lancet. 2022 Nov 1; 400 Suppl 1: S55S55.

BackgroundExposure to fast-food outlets (FFOs) is thought to relate to childhood obesity, but evidence is mixed and might be explained by imprecision in exposure measurement. We explored the effect of these differences by using novel geospatial analysis methods to study obesity rates of children living in a multi-ethnic, deprived location in the north of England.MethodsWe included 6260 children enrolled in the Born in Bradford cohort study who had participated in the most recent follow-up (2017-20), aged 6-12 years, and had BMI measurements (n=6260), body fat percentage (BFP; n=5004), and geolocation data for their home address. Informed consent was obtained from parents, and assent from children. Secondary points of interest data were used to classify and geolocate FFOs. We calculated proximity to FFOs using four contrasting methods including street network distance incorporating distance decay. We used linear regressions controlling for socioeconomic characteristics, including sex, age, ethnicity, mother's physical health, and perceived financial difficulties, with area-level deprivation; and built environment characteristics as controls. Complete data were available for 2883 children with BMI measurements and 2013 with BFP.FindingsWe introduced improved spatial precision in the quantification of exposure to FFOs, but this improvement did not lead to substantial differences in associations with BMI, or BFP, when comparing unadjusted associations of BFP and postcode buffers (correlation coefficient 0·08 [95% CI 0·05-0·11]) to BFP and address-based street network distance measurements (0·11 [90% CI 0·07-0·15]). After adjusting for confounders, exposure to FFOs close to home was not associated with an increase in BMI or BFP. Higher BMI was associated with increased maternal BMI (correlation coefficient 0·19 [95% CI 0·17-0·21]) and female sex (0·46 [0·22-0·70]); and comparable associations were observed for higher BFP, with an increased maternal BMI (correlation coefficient 0·40 [95% CI 0·34-0·46]), Pakistani ethnicity (2·89 [1·98-3·80]; reference white British), and female sex (2·90 [2·24-3·57]).InterpretationWe found no association between proximity to FFOs and obesity in children. Maternal predisposition and behavioural and sociocultural factors have a more important role in the development of childhood obesity. More research is required into the effectiveness of policies that ban FFOs.FundingUK Medical Research Council, UK Economic and Social Science Research Council, British Heart Foundation, ActEarly UK Prevention Research Partnership Consortium, and the National Institute for Health and Care Research.Copyright © 2022 Elsevier Ltd. All rights reserved.

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