March 10, 2010 -- Taxing junk food may help reduce obesity and improve health, researchers have found.
Patients got significantly less of their calories from soda or pizza when there was a 10 percent increase in the price of either, Penny Gordon-Larsen of the University of North Carolina at Chapel Hill and colleagues reported in the March 8 issue of Archives of Internal Medicine.
"Policies aimed at altering the price of soda or ... pizza may be effective mechanisms to steer U.S. adults toward a more healthful diet and help reduce long-term weight gain or insulin levels over time," the researchers wrote.
Talk of a soda tax has sparked debate across the country, particularly in New York and Philadelphia, where such legislation is currently under consideration. However, not much research has been done to study how price changes would affect health outcomes.
So the researchers looked at data from 5,115 patients enrolled in the longitudinal Coronary Artery Risk Development in Young Adults (CARDIA) Study from 1985 to 2006.
During that time, the inflation-adjusted price of soda and pizza actually decreased, with the largest drop observed for soda, falling from $2.71 to $1.42 for a 2-liter bottle -- a 48 percent decline.
In their analyses, the researchers found that changes in the price of soda and pizza were associated with changes in the probability of consuming those foods, as well as in the amounts consumed.
A 10 percent increase in the price of soda was associated with a 7.12 percent decrease in calories consumed from it, while the same increase in the price of pizza led to an 11.5 percent drop.
Price was also significantly associated with total caloric intake and body weight. A $1.00 increase in soda prices, for example, was tied to a mean of 124 fewer total daily calories, which amounted to an average weight loss of 2.34 pounds.
The researchers noted that similar trends were seen for pizza, adding that a $1.00 increase in the price of both soda and pizza together was associated with even greater changes in total energy intake, body weight, and insulin resistance.
"Our results provide stronger evidence to support the potential health benefits of taxing selected foods and beverages," they wrote. "Similar taxation policies have proven a successful means of effectively reducing adult and teenage smoking."
They calculated that an 18 percent tax on junk food would result in a 56-calorie decline in total daily energy intake. At the population level, that would translate to about five pounds per patient per year, along with significant reductions in the risks of most obesity-related chronic diseases, they said.
Since their study looked at only a small number of foods, they called upon researchers to assess more in future studies.
In an accompanying editorial, Dr. Mitchell H. Katz and Dr. Rajiv Bhatia of the San Francisco Department of Public Health wrote that taxing is "an appropriate method of correcting for health and other social costs not accounted for in the private market cost."
However, they added, in addition to taxing unhealthy foods, policymakers should consider ways to reward healthy behaviors.
"Sadly, we are currently subsidizing the wrong things, including the production of corn, which makes the corn syrup in sweetened beverages so inexpensive," they wrote. U.S. agricultural subsidies should instead "be used to make healthful foods such as locally grown vegetables, fruits, and whole grains less expensive."
"In the end," Katz and Bhatia concluded, "putting our money where our mouth is means aligning our economic incentives so that we always serve up the healthful choice."