A new study in the journal Health Affairs estimates that a penny-per-ounce tax on soft drinks and other sugary beverages could prevent about 240,000 cases of diabetes per year, and 8,000 strokes and 26,000 premature deaths over a decade (or 2,600 per year).
Yes, death by soda.
So the analysis got me thinking: Our behavior is hard to predict, right? I know mine is.
Today, that dime price hike for a tall Starbucks coffee may deter my stop for a late morning pick-me-up. Tomorrow? I might be back to my old habits. Or maybe I'll shop around and find a cheaper cup of joe.
We're fickle, inconsistent consumers. Similarly, if my favorite Honest Tea (Mango Green) is slapped with a sugar-drink tax, would I choose to drink water instead? Probably not.
It was with this skepticism that I phoned the author of the paper, Kirsten Bibbins-Domingo, a general internist at San Francisco General Hospital and an associate professor at the University of California, San Francisco, to ask her a simple question: How certain are you that these estimates are realistic (or in the ballpark)?
"That's always a good question when it comes to modeling!" Bibbins-Domingo told me. And as she talked me through her methodology, I began to understand how she and her team were connecting the dots.
When people consume lots of sugary drinks, "we know there's a risk of gaining weight," Bibbins-Domingo says. Studies have demonstrated this. "And we know weight gain is linked to increased risk of heart disease and [Type 2] diabetes." Soda consumption also seems to increase the risk of diabetes on its own. "This association has been observed consistently across a variety of studies," she says.
Bibbins-Domingo and her team relied upon findings from a range of observational studies and clinical trials that have evaluated these connections to figure out how many deaths a soda tax could prevent.
She also included data from the Framingham Heart Study, which has tracked the health of thousands of residents of Framingham, Mass., since the 1940s. And the team fed all these data into a computer model, which gave them their data on the health effects of the soda tax.
OK, this helps. But back to the questions about our unpredictable behaviors. Bibbins-Domingo acknowledges this is the big challenge. "We don't know what people will do," she says. But she and her team made what she thinks are some conservative assumptions.
In general, they assume that if the price of soda rises, people will buy less of it. "We assume that 40 percent of the calories saved by forgoing a sugary drink are replaced with other calories," she says, meaning either calories from drinks such as milk or fruit juice or from food. "So for every 100 calories in soda avoided, only 60 calories are actually lost in the diet."
This is not the first study to predict that a soda tax would be effective in reducing consumption. Yale University researchers concluded in this report that taxing sugary drinks would lead to economic benefits as well.
But researchers are divided. And there are also data suggesting that price manipulations would not be effective in trimming Americans' waistlines or getting us to eat better. As I reported back in 2010, a study done at the University of Buffalo found that mothers will buy more fruits and vegetables if the prices are deeply discounted. But if they save money on the healthful stuff, this means they have money left over. And what do they do? Buy more junk food.
I asked Len Epstein, chief of the division of behavioral medicine at the University of Buffalo, to take a look at the new Health Affairs paper. He told me he was impressed with the modeling and the analysis. But he says the paper may overestimate the effects of a soda tax.
"The concern, as noted by the authors, is whether people would just substitute another empty-calorie drink that was not taxed, or other types of junk foods that were not taxed, as substitutes for soda," says Epstein.
Prior real-world attempts to actually implement a soda tax haven't gone over so well. The District of Columbia came close in 2010. But ultimately, according to this Washington Post report, the City Council killed it.
And just this week, a physician in Portland, Ore., began rallying behind the idea that a penny-per-ounce tax on sweetened beverages could help reduce the heavy burden of lifestyle diseases. According to this report, Gregg Coodley is advocating for a soda tax ballot initiative in November in Multnomah County. But the American Beverage Association has called the proposed tax unfair and discriminatory.