Berkeley has a big new soda tax that won't reduce obesity

Berkeley voters approved the country's most aggressive soda tax Tuesday, giving a policy long-supported by public health experts its first shot at a real-life experiment.

(New England Journal of Medicine)

The Berkeley measure adds a one-cent-per-ounce tax to any sugar-sweetened beverages, which includes soda, sports drinks, and even syrupy coffee drinks like Starbucks' Frappucinos. It's a more aggressive measure of soda taxes tested elsewhere. Washington had a much smaller soda tax, 2 cents for a 12-ounce can. That tax had a short, six-month run in 2010 before voters rejected it in a ballot initiative.

The Berkeley measure and other soda taxes are a simple bet on economics: when something costs more, people will buy less of it. Soda consumption has more than doubled since the 1970s and this tax is an attempt to reverse that trend

But where soda taxes appear to fall short is with weight loss; no research has ever shown that a soda tax will help reduce obesity. This suggests that, even if a soda tax gets shoppers to ditch sugary drinks, they're replacing them with calories somewhere else.

Soda taxes reduce soda consumption

This is a point that comes out in study after study: people buy fewer sugary drinks when the price increases significantly.

In one study, researchers at a Boston hospital added a one-cent-per-ounce tax to sodas sold in its cafeteria (the same size tax that Berkeley has implemented). This was equivalent of a 35 percent increase in soda prices. During that time frame, soda sales declined by 26 percent — and some of that decline even persisted after the hospital went back to its initial prices.

in one experiment, a soda tax lead to sales falling by 26 percent

Repealing a soda tax, meanwhile, has correlated with an increase in consumption. Researchers found this in 2003 study of what happened when Ireland reduced its fee on sugary beverages. They saw a 6.8 percent increase in soda consumption when the tax decreased by 20 percent.

These are all double-digit price changes. And other studies have found that smaller increases aren't necessarily big enough to change behavior. One study published in the journal Health Affairs in 2010 found that the taxes states usually pursue — which often amount to a 4 percent price hike — were "unlikely to have measurable effects on soda consumption or obesity among children overall."

We don't know if soda taxes will reduce obesity

Reducing soda consumption is meant to be a key step towards a larger policy goal: reducing obesity rates. And on that issue, the evidence seems to be more mixed, suggesting that these taxes may not lead to weight loss. This is mostly due to people switching to other foods or beverages when they ditch soda. There's one study, for example, showing that soda taxes do reduce soda consumption — but that decrease is completely offset by increased drinking of other high calorie beverages like milk.

Another study looked at Maine, which had a "snack tax" from 1991 through 2001 (it included both snack food and soda) and compared the state's obesity rates to neighboring New Hampshire. It found no significantly slower change in Maine's obesity rate over that time period.

The most comprehensive look at this issue is a 2013 review article published in ClinicoEconomics and Outcomes Research. It combed through all the other studies that have been done to look at whether soda taxes could decrease obesity. Taken together, the findings suggested that "the effectiveness of a taxation policy to curb obesity is doubtful."

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