The researchers gave 100 study participants three different menus to order from, and asked to imagine what they would buy at a fast food restaurant or a movie theater. One had drink sizes ranging from 16 to 32 ounces. On a second menu, soda options ranged from one 16-ounce drink, a package of two 12-ounce drinks and a package of two 16-ounce drinks. A third menu only had one option: one, 16-ounce soda.
Soda pricing was equal among settings; that is, one 24-ounce drink and two 12-ounce drinks cost the same ($1.79, a price the researchers took from the McDonald's menu). So the whole idea was to see how customers might react to a bundle of small sodas versus one, larger drink.
What they found: Participants offered the bundled menu tended to order a larger amount of soda.
"These results show that businesses should earn significantly more revenue when bundles are offered than when small drink sizes alone are offered," the study authors write. "This means restaurants have a strong incentive to convert their original-sized drinks into bundles so they do not lose a major source of revenue."
This is obviously one small study and it also wasn't able to look at how much people would actually drink of the sodas they ordered, another important factor in determining calorie intake. It does provide some evidence though, that when it comes to soda, outlawing large sizes might not lead to the desired result.