Associations of the Philadelphia sweetened beverage tax with changes in adult body weight: an interrupted time series analysis.

Background: Sweetened beverage taxes are associated with large decreases in sugar-sweetened beverage sales, but their effects on weight outcomes are unclear. We examined associations of the 2017 Philadelphia beverage tax with changes in adult weight outcomes.

Methods: We obtained electronic health record data on adults 18-65 years old in Philadelphia (intervention) and other areas of Pennsylvania and New Jersey (control) from 2014 to 2019. Controlled interrupted time series models compared post-tax changes in trends of body mass index (BMI, primary outcome) and obesity prevalence (secondary outcome). A panel sample comprised 175,675 adults with at least one BMI measure in both the pre-tax (2014-2016) and post-tax (2017-2019) periods. A cross-sectional sample comprised 587,121 adults with at least one BMI measure from 2014 to 2019.

Findings: Before tax implementation, Philadelphia panel patients had a mean BMI of 30.4 kg/m and an obesity prevalence of 44.5%. After implementation, in the panel sample, there was a -0.03 kg/m (95% CI: -0.07, 0.02) per quarter decrease in BMI vs. control, implying a -0.32 kg/m (-0.85, 0.20) change at the end of the 3-year study period. In the cross-sectional sample, there was a -0.05 kg/m (95% CI: -0.09, -0.01) per quarter decrease in BMI vs. control, implying a -0.60 kg/m (-1.04, -0.16) change at the end of the study period. Results for obesity prevalence were consistent with the BMI results.

Interpretation: There was some limited evidence of a decrease in BMI and obesity prevalence in Philadelphia 3 years after beverage tax implementation. Replication of these results is needed.

Funding: National Institutes of Health.