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/m² and an obesity prevalence of 44.5%. After implementation, in the panel sample, there was a −0.03 kg/m² (95% CI: −0.07, 0.02) per quarter decrease in BMI vs. control, implying a −0.32 kg/m² (−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/m² (95% CI: −0.09, −0.01) per quarter decrease in BMI vs. control, implying a −0.60 kg/m² (−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.