People get emotional when you bring up the idea of a soda tax. Proponents of the tax are quick to compare it to excise taxes on cigarettes. They argue that it's a necessary measure for the sake of public health, pointing to the "externalities" of soda consumption as a justification for the apparent strangeness of a tax on a specific food item. And those against the tax are just as strident. They manage to appeal to conservatives and liberals alike, arguing that soda taxes force a nanny state's conception of nutrition on Americans and thereby limit freedom of choice -- and that soda taxes are regressive, hurting poor people more than they hurt the rich.
It's refreshing, then, to find that many scientists and public health experts are trying to cut through the rhetoric to find the empirical basis for arguments in favor of -- and against -- soda taxes. Such studies are, in their way, helping clear up some of the basic issues around the potential implementation of a soda tax before anyone can martial out their philosophical stances.
The latest such study comes from a group of researchers at UC-San Francisco and the Columbia School of Public Health and is published in this month's issue of Health Affairs. The researchers made some basic assumptions about the eating and drinking behavior of Americans and then, using a time-tested computer model of American nutrition and health, simulated the potential future impact of a national, penny-per-ounce excise tax on sodas. That's the form of soda tax that many proponents -- most notably Kelly Brownell of Yale -- think would be most effective and fair.
The simulation predicted that the tax would avert 2,600 deaths, 9,500 heart attacks and 240,000 new cases of diabetes every year. The introduction to the study cited numbers over the first 10 years of adoption, so some news sources initially picked up figures ten times as high, which would be somewhat outlandish. But even the real numbers are eye-popping. The same number of people -- 2,600 -- die of all heart diseases in New Hampshire in a year, for example.
Kirsten Bibbins-Domingo, lead writer of the study, told The Huffington Post that attributes the lives saved to two sources above all: lower median weight and decreased risk of diabetes.
The lower weight is relatively self-explanatory. A penny-per-ounce soda tax on sugar-sweetened beverages would likely raise the shelf price of soda by about 20 percent, according to past empirical work on soda. And Bibbins-Domingo's new study estimates that such an increase "would reduce consumption ... by 15 percent among adults age 25 to 64." The study estimates that 40 percent of the ensuing calorie reduction would be offset by calories from beverages such as milk and fruit juice, but that for the other 60 percent, people would switch to calorie-free drinks like water and diet soda.
The net effect of these changes would be to reduce average daily energy intake by 0.9 calories. That may not sound like much, but, over the course of a year, it would lead to an average weight lose of about a pound, which the study says would move almost 900,000 adults out of obesity range.
Still, the soda industry was quick to seize on the moderateness of this weight loss as a reason to discredit Bibbins-Domingo's research.
"Using assumptions based on ‘lacking or inconclusive’ evidence, the authors estimate their proposed tax would result in an average weight loss of less than one pound per year -- an insignificant amount for an obese person," wrote the American Beverage Associate in a statement on the study to The Huffington Post.
Other studies have indicated that a soda tax wouldn't even have that sizable an effect on weight loss. A 2009 piece in the Journal of Public Economics, from a team headed by Jason Fletcher of the Yale School of Public Health, examined the impact of extant taxes on soda across the country, to see how people respond to the relatively low sales and excise taxes already in place. Their research found that people do respond to soda taxes by drinking less soda -- but that the decrease is entirely offset by increased consumption of caloric beverages like milk and fruit juice. That means that, according to their model, a soda tax would not reduce obesity.
"We're in total agreement that prices matters, that taxes matter," Fletcher told The Huffington Post. "What's really key is what people drink instead. ... That's really a core issue."
Bibbins-Domingo admitted that the biggest cause for uncertainty in her paper is the assumption of 60 percent calorie reduction. But she argues that reduced consumption of soda would still be positive because such a reduction would also decrease diabetes rates.
"Sugar-sweetened beverages seem to be diabetes-promoting independent of weight gain," she told The Huffington Post. "Whether it's the high fructose corn syrup or some of the other additives, studies have shown an impact that's not dependent on the amount of weight that's gained. So a soda tax is likely to have a large overall effect even though the weight loss is small."
Bibbins-Domingo also pointed to recent studies that have linked soda consumption to hypertension, again beyond soda's relationship to weight gain.
Though Fletcher was quick to note that correlation -- between diabetes and drinking soda, for example -- is not causation, he admitted that his study modeled only for weight, not for these other diseases. And he said that his team had looked at the effect of relatively small taxes, so it's possible that a large tax levied on producers -- and thus visible before checkout -- of the kind that Bibbins-Domingo was investigating, could have a disproportionately large effect than the kinds of sales taxes that have already been put into place.
Renowned food policy expert Marion Nestle also said that the study helps confirm her long-held opinions on soda taxes. "The study looks like a prediction model; it’s not actually what necessarily happens," she wrote in an email. "Even so, it suggests that taxes are well worth a try as something that might do some good."
And Bibbins-Domingo noted, as past supporters have, that one advantage of taxing soda -- as opposed to something like red meat -- is that soda doesn't have any positive health benefits.
"There really is no evidence of any benefit and there is evidence of harm," she said. "We don't know exactly how people might change their consumption patterns, but I do think these studies show that overall, a soda tax would help things out. There are a lot of possible interventions, but this would be a good start."
And then, of course, there's the money. According to Bibbins-Domingo's study, a penny-per-ounce tax would generate about $13 billion in tax revenue per year -- no small sum in a time of fiscal uncertainty. That could go a long way towards putting a dent in the estimated $80 billion America spends on health care for the overweight and obese nationwide.
Many of those most affected by this increased cost, not incidentally, find themselves living on the lower rungs of America's economic ladder. And it's for that reason that Bibbins-Domingo disagrees with the critics who say that a soda tax is regressive.
Responding to that common criticism, she said, "The health benefits of these types of policy would accrue to that same group that would be affected by this type of intervention."