The researchers came to their conclusion after analysing data on household food purchases made by Americans in 2006. The findings were published in the American Journal of Agricultural Economics.
"Instituting a sugary-beverage tax may be an appealing public-policy option to curb obesity, but it's not as easy to use taxes to curb obesity as it is with smoking," study lead author Chen Zhen, a research economist at RTI International, said in a journal news release.
"Consumers can simply substitute an untaxed high-calorie food for a taxed one," Zhen said. "And as we know, reducing calories is just one of many ways to promoting healthy eating and reducing nutrition-related chronic disease."
In the United States, about 36% of adults and 17% of children and teens are obese. A previous RTI study found that medical costs associated with obesity are R1440.63 billion or more per year.
A soda tax has been proposed by public-health advocates who hope higher prices will deter unhealthy food purchases.
Taking another approach to combat obesity, New York City Mayor Michael Bloomberg attempted to ban the sale of many large-size sweetened drinks, but the effort has been struck down twice, most recently by an appeals court. The higher court ruled that the city's Board of Health did not have authority to approve the soda restrictions. The rule was also flawed by loopholes and exemptions, the court said.
For the current study, the researchers also looked at differences between lower- and higher-income households. Foods and beverages purchased by lower-income families tended to be higher in calories, fat and sodium content than those bought by higher-income families.
"Because lower-income families tend to buy more sugary soft drinks than higher-income families, they would more readily reap the health benefits of reduced sugary-beverage intake," Zhen said. "However, they would also pay more in beverage taxes, making it a regressive tax."
The study was funded by the Robert Wood Johnson Foundation and the US National Institutes of Health.
The U.S. National Heart, Lung, and Blood Institute has more about overweight and obesity.