Can Sin Taxes Halt and Help Reverse the Obesity Epidemic?

By Stewart Lonky, M.D. 

Is obesity the biggest threat to the nation's health?

That's what Mercedes Carnethon, Ph.D., the chief of Epidemiology at the Feinberg School of Medicine at Northwestern University writes in a recent issue of Scientific American.

Dr. Carnethon will get no argument from me. She is correct in my estimation in singling out obesity as the country's most significant health threat, even outpacing tobacco use as the leading cause of preventable death and disability.

Just look at the numbers. As of today, 4 in 10 U.S. adults –and 20 percent of children and teens—are obese, and two-thirds are overweight. Obesity and overweight are associated with increased risk of 13 types of cancer, accounting for about 40 percent of all cancers diagnosed in the United States. Across a lifetime, obesity contributes to the development of other illnesses as well, including cardiovascular diseases and lung disease, mental illnesses such as depression, and many disabilities, including osteoarthritis.

So Dr. Carnethon, along with many others, was among the first to cheer the findings of a recent study describing the effectiveness of a beverage tax on lowering the consumption of sugar-sweetened beverages in Philadelphia, one of the nation's poorest and most obese cities. Sugary drink sales plunged 38 percent after the city levied the tax, according to the study. 

While a tax on obesity-promoting foods seem like a good idea, what are we to make of this study?

It would seem that the logical first step in reducing or preventing obesity would be individual behavior changes that encourage healthy lifestyles. Nearly two years in, we can better assess the effectiveness of Philadelphia's sugary drink tax.

The tax, implemented in 2017, comes to 1.5 cents per ounce, equal to a hefty $1 tax on a typical $1.56, two-liter bottle. The city included artificially sweetened “diet” sodas in the tax while excluding sugary fruit juices. 

But as MarketWatch columnist Brett Arends points out, the tax, rationalized as a kind of “sin tax” in the war on obesity, did almost nothing for people’s health. According to a separate study, Philadelphians didn’t cut calories as a result of the tax on sweetened drinks, nor did they shift towards healthier alternatives. 

Instead, most residents just drove outside the city to buy the same old sodas from stores where they didn’t have to pay the tax. Meanwhile, the city's poorest residents — those who would find it hardest to drive for many miles to buy soda — "just ended up paying more in taxes," Arends notes. 

To summarize, the tax on sweetened beverages harmed local businesses and achieved none of its stated health goals.

The Philadelphia experiment points out some very basic facts about human nature, as well as the challenges faced in dealing with the obesity problem. No matter when we decide to make changes — or how strongly we're motivated — adopting new, healthier habits, or breaking old, bad ones, can be difficult. Old habits die hard, so the saying goes, especially when it comes to engrained eating behavior.

To some extent, habits are beyond our conscious control. Our brain's neuronal circuitry reflects everything we do, feel, and think. Neurons, or brain cells, communicate with each other at gaps, called synapses. Neurons communicate chemically by releasing neurotransmitters into these synaptic spaces, where they're picked up by the next neurons' receptors. The human brain contains billions of neurons—each connecting with up to 10,000 other neurons, resulting in trillions of synaptic connections. These interconnected neurons become circuits that underlie our habits.

The more we do something—eating salty snack foods while watching TV, playing a sport or musical instrument, studying math—the stronger the neuronal circuit becomes that supports these habits. Once neuronal circuit forms, when one neuron fires, the others fire as well—strengthening the whole circuit. This pattern, known as Hebbian Theory, states that "neurons that fire together wire together." Neuronal circuits maintain our habits, and our habits strengthen those neuronal circuits. The bio-behavioral influence goes both ways.

Given the reality of human biology, combined with social and structural barriers that constrain individual choice, environmental factors, developmental determinants and genetic and epigenetic influences on weight gain, how can we expect sin taxes, such as those on sugared beverages, to positively influence unhealthy behaviors, much less make a serious dent in the obesity epidemic?

While a sugar tax should work in theory—some people might stop and consider whether they need a two-liter bottle of soda if it costs more—and whether they are willing to pay more to have it now.  For people on a budget—I don't see how these "small changes can morph into lifestyle patterns that have a large effect on the environment and culture around obesity," as Dr. Carnethon suggests.

Population-wide obesity prevention measures will only work if we come up with a complex, comprehensive policy that deals with the multiple reasons we gain weight in the first place. Yes, obesity is a complex, multifactorial disease that can't be palliated with half-hearted measures. 

And that, as Dr. Carnethon, writes, "is no small matter." If the opposite were true, we wouldn't have record high obesity rates in this country.