Fat that fizzes or analyses that fizzle?

The premise behind taxing soda is simple: We shouldn’t be drinking so much of it. Why? Because soda that isn’t artificially sweetened contains sugar (“sugar” here is used interchangeably with corn syrup or other caloric sweeteners), and though sugar is a valuable source of energy, it will end up being stored as fat if we don’t expend all the energy we take in. This is the simplest explanation. Other, more complex explanations summarized by Bachmann et al. (2006) include the possibility that sugared beverages impose a high glycemic load (a measure of a food’s impact on blood sucrose levels), which leads to increased weight gain; that liquid forms of energy may do a poor job of satiating hunger, which means people will not automatically compensate by decreasing consumption of other foods; and that “increased sweetened beverage intake displaces milk intake, which may inhibit the possible obesity-reducing role of calcium.”

If we look at the history of increasing weight gain in the US, we also see a corresponding increase in the consumption of sugared beverages. According to the Department of Agriculture, our consumption of soda has increased, per capita, by 500 percent over the last 50 years. Estimates as to how much this consumption contributes to our energy intake range from 7 to 15 percent.

Thus, soda tax proponents have argued that soda – or rather the entire class of sugar sweetened beverages or SSBs (the terms soda and SSBs will be used interchangeably throughout) – has contributed to our collective weight gain, fueling obesity and all its related health problems, notably diabetes. If we tax soda, we will reduce consumption and either lose weight, or not gain additional weight, thereby addressing, at least in part, the adverse health effects associated with these conditions. Even small reductions in weight will prevent some people from developing diabetes, while the burden of a tax on people who consume optimally (which is to say, keep their energy intake and expenditure in balance) will be offset by their benefiting from the overall reduction in health care costs to society.

This all sounds rather straightforward and, indeed, persuasive. But while you start with two indisputable facts – that there has been a significant increase in soda consumption and that there has been a steady increase in weight gain and obesity in the US – you have to show that they are related: that the first is causing the second, or at least causing it in some part. Assuming you are able to do this, you will have to determine how they are related: Is soda primarily responsible for weight gain or just one of many factors? Is weight gain from soda consumption an aggregate problem (it affects everyone) or is it only a problem for some groups of people? This is an essential step in order to establish how a restriction on consumption might work. If you can show that reducing soda reduces weight for everyone, or even just for a subset of people, then you have to show how a tax would achieve that reduction.

This is the challenge facing soda tax advocates. But when soda taxes are discussed in the media these challenges are simplified:

  1. Increased soda consumption has contributed to the increase in weight gain and obesity.
  2. A tax on soda will reduce consumption which will lead to weight loss and a reduction in weight gain and obesity.
  3. Therefore, a tax on soda is the most effective way to reduce obesity.

We will argue that such accounts are formulaic and simplistic. They don’t do justice to a complex issue that has neither been adequately explored by the media, nor understood by policy makers who push for tax-centered solutions. We also will explore how the debate has been dominated by a small cadre of scientists in one scientific field, at the expense of other scholars and relevant fields of study.


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