City-Level Sugar-Sweetened Beverage Taxes and Changes in Adult Body Mass Index.

Abstract

Importance: Sugar-sweetened beverage (SSB) excise taxes are popular policy interventions aimed at decreasing SSB purchasing and consumption to improve cardiometabolic health and generate revenue for public health initiatives. There is limited evidence that these taxes in the US are associated with weight-related outcomes in adults, a primary contributor to cardiometabolic health.

Objective: To determine the association between SSB excise taxes and adult body mass index (BMI) and proportion of adults with overweight or obesity among California cities and assess whether associations vary by demographic characteristics.

Design, setting, and participants: This cohort study compared California cities with SSB taxes (Albany, Berkeley, Oakland, and San Francisco) and demographically matched cities without SSB excise taxes from 6 years before the tax and 4 to 6 years after the tax from January 2009 through December 2020 using electronic health record data. Participants were Kaiser Permanente (KP) members aged 20 to 65 years at cohort entry with at least 1 pretax and 1 posttax BMI measurement. Data were analyzed from January 2021 to May 2023.

Exposure: Implementation of city-level SSB excise taxes.

Main outcomes and measures: Mean BMI and proportion of adults with overweight or obesity. Analysis used the differences-in-differences (DID) method.

Results: The cohort had a total of 1 044 272 members (178 931 participants in 4 cities with excise taxes; mean [SD] age, 39.7 [11.2] years; 99 501 [55.6%] female; 865 343 participants in 40 control cities without excise taxes; mean [SD] age, 39.9 [11.6] years; 480 155 [55.5%] female). DID estimates for mean BMI showed a modest decrease among adults aged 20 to 39 years (20-25 years: -0.30; 95% CI, -0.51 to -0.08; 26-39 years: -0.19; 95% CI, -0.37 to -0.20), female participants (-0.19; 95% CI, -0.26 to -0.11), and White participants (-0.19; 95% CI, -0.35 to -0.04) living in cities with SSB excise taxes. There was a statistically significant reduction in mean BMI in Berkeley (-0.16; 95% CI, -0.27 to -0.04). There were no overall differences in BMI or proportion with overweight or obesity.

Conclusions and relevance: In this cohort study, SSB excise taxes were associated with reduced mean BMI among adults in demographic subgroups, including in young adults who consumed the most SSBs, and in Berkeley. Future research should examine the mechanisms of these associations to inform how SSB taxes could be more equitable for weight-related outcomes.