Mayor Ed Murray’s tax would exempt diet drinks, and data show it could place a heavier burden on the people the tax is supposed to help. The tax would apply only to sugary beverages, and for a 2-liter bottle of Coke, it could add $1.35 to the cost.

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Mayor Ed Murray’s proposed tax on sodas exempts one kind of soft drink more typically favored by an affluent, educated and white population in Seattle and beyond: diet drinks.

The 2-cents-an-ounce tax would apply only to sugary beverages, such as regular sodas, energy and sports drinks, and bottled teas and coffee that are sweetened with sugar. For a 2-liter bottle of Coke, the tax could add $1.35 to the cost.

Money raised — estimated at $16 million per year — would be used to support various programs aimed at reducing disparities between white students and black and Latino students.

But this proposed tax could also place a heavier burden on the very groups it’s aiming to help.

Market data show significant racial and ethnic differences in patterns of consumption between sugar-laden beverages and their artificially sweetened counterparts.

When surveyed by research firm Nielsen Scarborough, 70 percent of Latinos and 66 percent of blacks in the Seattle area said they’d consumed a sugar-sweetened soft drink in the past seven days, compared with just 54 percent of whites and 56 percent of Asians. This disparity is consistent with national data.

Regular consumers of sugary drinks are also poorer and have lower levels of education, on average.

But diet drinkers have a very different demographic profile.

Sugar-sweetened soft drinks are more typically favored by blacks and Latinos, and by people with lower incomes and less education. In contrast, whites and Asians are more likely to drink diet sodas, as are people with higher incomes and more education.

Asians and whites consume artificially sweetened beverages at a slightly higher rate than blacks or Latinos.

Adults who regularly drink sugar-free sodas are more likely to have a college or graduate degree, and they’re also a lot wealthier. In the Seattle area, they have a median household income more than $10,000 higher than that of folks who favor sugary drinks.

The survey data also showed the Seattle metro area ranks very low for the rate of consumption of sugary drinks — 75 out of 77 markets.

According to Benton Strong, a spokesperson for the mayor, the proposed tax is intended to have a public-health benefit. Sugar-laden drinks have been identified as a major cause of obesity and type 2 diabetes, so the tax could act as a deterrent.

When surveyed, 56 percent of adults in the Seattle area said they drank a sugar-sweetened soda, energy or sports drink, or bottled tea within the past seven days. That ranks Seattle third lowest among 77 markets.

But if the assumption is that diet drinks are a healthier choice, the evidence increasingly suggests they are not.

Many researchers now say that drinking diet soda does not help with weight loss, and could in fact contribute to obesity and type 2 diabetes, just like regular sodas. There are more questions than answers regarding the long-term effects of consuming these artificial sweeteners, but there is enough concern for the Harvard School of Public Health to conclude: “Diet soda may not be a healthy substitute for sugary soda.”

In January, a soda tax similar to the one proposed for Seattle went into effect in Philadelphia — the first in a major U.S. city. But there are a couple important differences.

Philadelphia’s tax is a little lower, at 1.5 cents per ounce, but it is also broader, applying to both sugary and diet soft drinks. The approach spreads the burden more evenly among racial and income groups.

According to Strong, the city will analyze the proposed tax’s impact on racial equity before releasing the final plan.