In a move lauded as "heroic and historic," Philadelphia recently became the first major U.S. city to pass a soda tax, and the first municipality to include diet sodas in the tax.

It was in Philadelphia, over 200 years ago, that Benjamin Franklin wrote that nothing is certain except "death and taxes." Yet Philadelphia's soda tax was far from certain as similar measures had previously failed.

Why the fuss? Political and ideological objections aside, there is strong evidence that the tax is good news for public health in Philadelphia, a city with a significant obesity problem.

Obesity
Obesity is a medical term to indicate when someone has a body mass index (BMI) ≥ 30 (calculate your BMI here). Obesity is both a public health epidemic and a tremendous drain on health care resources. This is particularly true for Philadelphia, where 68% of adults and, in some neighborhoods, about 70 percent of kids, are either overweight or obese.

Soda and health
Obesity is a complex issue with multiple causal factors, but the evidence that soda is a significant contributor to obesity is overwhelming. Part of the problem is that liquid sugar is not as filling as "regular food." A Big Gulp 32-ounce soda has 91 grams and 364 calories of sweetener, yet after we drink that 364 calories of soda…research shows we are unlikely to eat 364 fewer calories of food.

In addition to obesity, regular soft drinks have been linked to health problems. Consider that people who drink 1-2 cans of day of soft drinks have a 26 percent greater chance of developing Type II diabetes. Even men who regularly consume one sugary beverage a day have a 20 percent greater chance of having a heart attack than those who rarely consume sugary drinks.

The economics of soda
While the rates of soda consumption nationwide have been dropping, soft drinks are still popular in Philadelphia. In fact, Philadelphians consume about 60 million gallons of sugary beverages a year. Cost is a key factor. The price of a 2-liter bottle of soda has not kept pace with inflation; you can still get a 2-liter bottle of soda for under a $1.

The soda tax should decrease soda consumption
While soft drinks are currently widely consumed in Philadelphia, after the tax takes effect, consumption is projected to decline. That's because as the price of a non-essential consumable item climbs, we buy less of it. We've seen this to be true for cigarettes and recently for sugary drinks. After Mexico instituted a soda tax, their soda consumption declined 12 percent.

Effects of decreased soda consumption
Based on analyses by the Childhood Obesity Intervention Cost Effectiveness Study (CHOICES) led by Harvard professor, Dr. Steven Gortmaker, Philadelphia's Health Commissioner, Dr. Tom Farley, estimates that over a 10-year period, the soft drink tax will lead to approximately

  • 18,000 fewer cases of obesity
  • 350-440 fewer deaths
  • $98 million decrease in medical costs
  • >1,000 fewer cases of Type II diabetes a year

And that's why so many public health advocates support the tax. While educating the public on sugary beverages is important, knowledge alone doesn't change behavior.

Simply advising people to "eat less, exercise more" and practice more "personal responsibility" has been inadequate at best, patronizing at worst, and wholly ineffective at solving our obesity problem. The soft drink tax economically alters our environment, and environment powerfully influences eating and drinking.

As the new legislation taxes both sugar-sweetened and artificially sweetened beverages, the tax is likely to decrease soft drink consumption in Philadelphia over the next decade.

To quote the city's Health Commissioner, Dr. Tom Farley, "People will be less likely to switch from sugary drinks to diet drinks, but they may be more likely to switch from sugary drinks to water, and that is what we want."

Stacey C. Cahn, PhD is associate professor of clinical psychology at the Philadelphia College of Osteopathic Medicine (PCOM). Dr. Cahn specializes in eating disorders, obesity, and cognitive-behavioral therapy.

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