People are generally more likely to pass on high-kilojoule food when there is a tax on it, though it might not matter to everyone, a small study suggests.
In a computer-based experiment with 178 US college students, researchers found that the students generally "bought" fewer lunchtime kJ’s when sugary, high-fat fare came with a tax of 25% or more.
The exception was when kJ-conscious eaters were given kJ information on their lunch options, the tax did not seem to sway their decisions.
Junk food taxes and greater openness about energy information have both been advocated as ways to help consumers limit their calories and, hopefully, keep their weight in the healthy range.
In the US, proponents of taxes on soda and junk food argue that it would not only discourage people from buying them, but could also help offset the estimated $147 billion cost of treating obesity-related ills.
Supporters also point to research suggesting that cigarette taxes have helped curb tobacco use.
Policies to require restaurants and other vendors to be frank with calorie information have made greater gains. In 2008, New York City became the first US city to mandate that fast-food and coffee chains put kJ information on their menus. And in 2010, the federal healthcare reform law set national labelling requirements for certain restaurants and vending machines.
But just how effective such measures have been, or could be, is controversial.
A study, for example, found that New York City's law has so far done little to change children and teenagers' eating habits at fast-food restaurants.
The current study, reported in the American Journal of Clinical Nutrition, suggests that the effectiveness of junk food taxes might partly depend on whether calorie information is given or not -- and the customer's own calorie-consciousness.
For the study, researchers led by Dr Janneke Giesen of Maastricht University in the Netherlands, had 178 US college students choose a hypothetical lunch from a computer menu on three separate occasions.
Each time, the prices for high-kJ items: bacon cheeseburgers, brownies and chips; were increased, first by 25% and then 50%.
About half of the students were given energy information at all lunches, while the rest were not.
Overall, students tended to order fewer kJ when a junk food tax was in place. They curbed their average kJ intake by about 420 to 1260 kJ, depending on the tax in place.
kJ savvy peers
The only students who did not respond to the price increases were those who were already watching their diets and were given kilojoule information. They ate fewer kJ’s than their peers without any food tax, and showed little change in their eating behaviour when taxes were added.
"The most important finding of our study is that a tax of 25% or more on (high-kJ) foods makes nearly everyone buy fewer kilojoules," Dr Giesen said.
For people who are weight- and diet-conscious, calorie information might trump price, according to Dr Giesen. "However, if one wants to help people in general to prevent caloric overconsumption," Dr Giesen said, "then our results indicate that imposing a high tax on food items is much more efficacious."
Limitations to the study
A researcher not involved in the study noted that it had a number of limitations, including a small sample size.
Still, it fits with larger experiments, suggesting that food taxes might work, said Dr Barry Popkin, a professor of nutrition at the University of North Carolina, Chapel Hill, who has studied the potential effects of junk food taxes on people's food choices.
Popkin pointed to a recent study by Harvard researchers in which they added a 35% tax to sugary sodas sold in the cafeteria at Brigham & Women's Hospital in Boston. They found that sales of sugar-sweetened sodas dropped by 26%, and that people tended to replace those drinks with diet soda or coffee.
In contrast, an educational campaign, where signs were posted, recommending that people cut back on sugary soft drinks, failed to make a dent in sales.
According to Dr Giesen, studies are still needed to see whether smaller tax increases –something closer to 10%, which would be more politically viable, influence people's buying habits.
Industry trade groups like the American Beverage Association and anti-tax activists like Americans Against Food Taxes (which has industry backing) argue that there is no evidence that junk food taxes will fight the US obesity problem. They also assert that such taxes will only unduly burden low-income families.
(Reuters Health, Amy Norton, February 2011)