The study, which was conducted by a team of researchers at Johns Hopkins University and published in the American Journal of Public Health, focused on black teenagers, who consume on average more than twice the recommended daily intake of sugar-sweetened beverages. It measured the effect of four different signs, which were hung in the soda aisle at six Baltimore corner stores. One of them reminded consumers about the amount of sugar contained in a bottle of soda, another reminded consumers about the amount of calories in that same bottle, and the other two expressed the amount of exercise it would take to burn off the energy in a bottle of soda (one in minutes of running, the other in miles of walking).
This is what the labels looked like:
"Our results showed that providing information in the form of miles of walking to burn off a 20 ounce bottle of soda or fruit juice had a modest, but significant, effect on reducing the number of calories compared with other relative information in the form of minutes of running or teaspoons of sugar."
In other words, nothing worked as well as telling people how far they would have to walk to "walk off" a bottle of soda (in this case, 5 miles). Which is saying something, because overall the signs worked incredibly well. Although the walking sign proved the most potent, providing context or even a simple reminder about the sugar and calorie content had a considerable affect on the average number of calories purchased — the average number of calories bought dropped from 149 calories before the signs were posted to 121 calories after.
Specifically, people bought fewer large sodas and sports drinks, opting instead for small fruit drinks, waters, 100 percent juices, and often even no beverage at all. Notice the steep drop in soda purchases and increase in "no drink" in the chart below.
It's worth noting that the study was limited in at least one important respect—it was focused on urban, Black neighborhoods in one city, and limited to adolescents. But given that that demographic tends to drink a comparatively large amount of soda the results are still relevant, and could suggest broader results if the study were expanded to include a more general demographic.
The surface-level takeaway is fairly straightforward: People are more discerning about their purchases when they are reminded, loudly, of the consequences. Whether that finding can be successfully implemented to encourage more responsible consumption remains to be seen. New York City's foray into the world of visible calorie counts, after all, hasn't gone as well as planned. Ever since the city began forcing food chains to post calorie counts on menus, there have been at best mixed results. A study by Brian Elbel, a population-health expert at New York University’s school of medicine, found "no meaningful difference" in purchasing habits. A separate survey by the city found that 11 chains saw calorie reductions, while 7 others did not (and one, Subway, noted the opposite: a calorie increase).
What's more interesting, and might be a worthwhile consideration for future calorie labeling legislation aimed at curbing the amount of unhealthy foods Americans buy, is just how successful a bit of context can be. If sharing the amount of exercise necessary to burn, say, a 240 calorie bottle of Coca-Cola stands to have a big (and positive) impact on whether or not consumers choose to buy that bottle of cola, it could be a useful trick in curbing the amount of soda Americans still drink (which is still too much), especially given how effective it was with some of the country's biggest soda drinkers.