Soda Taxes: Less Soda, Same Waistlines

There remains little doubt that an increase in the price of sugar-sweetened beverages, SSB, results in fewer purchases. However, as I have pointed out in the past, decreased purchases, while they may represent lower consumption, have yet to be associated with any health outcomes. A new study in JAMA Network Open looks at the four cities in California with an SSB tax of 1 cent per ounce. 

The researchers used the electronic health records from Kaiser Permanente of adult patients with a documented BMI before and after the institution of SSB taxes in 2017. Patients in the Kaiser Permanente system in Southern California acted as the controls matched for the usual variables. The researchers hypothesized “that cities with SSB taxes would have lower BMI after tax implementation compared with the control cities.” 

• Across all cities with sugar-sweetened beverage (SSB) taxes:
  • There was no significant change in mean BMI before and after tax implementation compared to control cities.
  • There was no significant change in the proportion of adults who were overweight or obese. There was a slight increase in the high-poverty sub-groups – a targeted at-risk population 
• When demographically stratified, there was a mean reduction in BMI among:
  • Adults aged 20-39 years
    • Females
    • White individuals
    • In Berkeley, a reduction was seen in year 5 after tax implementation compared to its control cities. [1]

The hypothesis, as stated, was wrong: an SSB tax did not result in lower population-wide BMIs. But might the researchers find a silver lining to this grey cloud?

They begin by lightly torturing the data, noting that the overall change, while not statistically significant, “was in the expected direction” and that “the hypothesized benefits of SSB taxes are not equally distributed among residents.”

Then, water-boarding as they extended their hypothesis:

“We hypothesized that SSB taxes are associated with weight through a sequence of increased consumer prices, decreased purchasing, and decreased consumption of SSBs but also by funding nutrition programs and raising awareness about the health harms of SSBs.”

This allows them to take a step back and note that SSB consumption is not the only influence on body weight, noting the investment by the four cities in health-related goals, e.g., access to healthy food, child development, and community infrastructure. In Berkeley, the $9 million raised went primarily to education programs, which certainly is valuable but does not support a direct link between taxation and an improved health outcome. 

In their discussion echoing back to the unequal distribution of SSB tax benefits, which parenthetically makes it a regressive tax, they note that “men, Hispanic and non-Hispanic Black adults, and low-income adults,” all at-risk, face “disproportionate targeting in SSB advertisements.” Presumably, marketing was more effective than the additional education SSB taxes fund. 

Finally, the researchers turn to the mathmagic of a computer simulation showing that doubling the tax would increase the reduction in BMI, resulting in “266 000 cases of obesity prevented by 2032. California, with one of the lowest rates of obesity in the country, at 28.2%, has 8.4 million obese individuals currently. That would be a 3% overall reduction, especially for the at-risk. If only the model captured the same reality as the study. It does not. 

Taxing soda might make people rethink their beverage choices, but it’s not exactly a magic bullet for public health. While researchers crunch numbers and dream up hypothetical futures with thinner waistlines, the reality remains: obesity is a complex beast, and sugar taxes alone won’t slay it. A reduction in BMI seen in the youngest of the cohort may indeed pay health dividends down the road. However, whether this can be attributed solely to a tax is uncertain.

[1] There were significantly fewer overweight and obese individuals in Berkeley than the controls, to begin with. 

Source: City-Level Sugar-Sweetened Beverage Taxes and Changes in Adult Body Mass Index JAMA Network Open DOI: 10.1001/jamanetworkopen.2024.56170