Portion Sizes and Sugary Drinks

Will policies aimed to limit intake of sugary drinks actually work?

Posted Jun 02, 2017

clubcola via Wikimedia Commons
Source: clubcola via Wikimedia Commons

There is a growing consensus that high doses of sugar can cause serious health problems.  Sugar contributes to obesity and diabetes.  One of the best delivery mechanisms for sugar is calorie dense drinks like soda, lemonade, and sweetened iced tea.

Because sugary drinks can lead to health problems, researchers and policy makers have begun to focus on ways to limit the amount of these drinks that people consume.  For example, New York City tried to ban large drink containers in the hope that it would reduce consumption.

A paper in the May 2017 issue of Psychological Science by Leslie John, Grant Donnelly, and Christina Roberto explored a few ways of trying to implement portion limits on sugary drinks to see whether they would work. 

One study looked at the concept of bundling.  The idea behind bundling is that when there is a limit on the maximum size of a container, stores might choose to sell “large” drinks that consist of two smaller containers for the price of a large drink. 

In this study, participants were given $0.40 at the start of the study and were told they could use it to purchase a drink they could consume during the study (and only during the study).  They were given the option of two sugary drinks (lemonade and iced tea).  Some participants were given a typical situation from restaurants:  the option to get a medium drink in a 16 oz. cup or a large drink in a 24 oz. cup.  Other participants were in a bundled condition.  The medium drink option was a 16 oz. cup, but the large option was two 12 oz. cups.  Some participants ordered their drink at a desk at the front of the room (like a fast-food restaurant).  Other participants ordered their drink from someone who came around and served them (like a regular restaurant).  The experimenters measured how much the participants drank. 

In this study, about 60 percent of participants ordered a drink. Of those who ordered a drink the majority selected the medium rather than the large.  However, participants were more likely overall to select the large drink in the typical condition (with the 24 oz. cup) than in the bundled condition (with two 12 oz. cups) regardless of whether they ordered at a counter or had the drinks served to them at a table.

This study suggests that limiting the size of the largest cup could decrease the amount of sugar people consume. 

The researchers then explored a second way of implementing portion limits.  In this study, the typical situation (a 16 oz. medium and 24 oz. large) was compared to a free refill condition in which participants got a 16 oz. cup, but could be refilled as often as the participant desired.  In this study, drinks were delivered to participants at a table as is typical at a sit-down restaurant.

Again, about 60 percent of participants elected to buy a drink, and again about 40 percent of people elected to get the large drink.  Unsurprisingly, people who got a large drink consumed more calories than those who consumed a small drink.  However, participants who got the free refills consumed far more calories than those who got a single 24 oz. cup.

In a final set of studies, the researchers repeated this design and added a self-serve condition in which participants who opted for free refills had to get up from their chair during the study and go to a table across the room (about 20 feet away) to get their refill.  Participants in this free refill condition also consumed more calories on average than those who got a 24 oz. cup but fewer calories than people who had “waiter” service. 

This study suggests that using free refills as a way of limiting the size of containers would backfire.  People given the option for free refills would likely consume more calories than people who are given a single larger container for a sugary drink.  Consumption with free refills would be particularly high when a waiter is delivering the drinks and so getting the refill requires no effort on the part of the consumer.

Research like this is important, because there are many well-intentioned policies that lead to unforeseen consequences.  Just because a consequence was unforeseen does not mean that it was unforeseeable.  Instead, using research to explore how policies affect people is a crucial step in developing policies that solve the problems they were intended to address.

Follow me on Twitter

And on Facebook and on Google+.

Check out the Two Guys on Your Head book Brain Briefs.

And my books Smart Thinking, Smart Change and Habits of Leadership

Listen to my radio show on KUT radio in Austin Two Guys on Your Head and follow 2GoYH on Twitter and on Facebook.  The show is available on iTunes and Stitcher.


John, L.K., Donnelly, G.E., & Roberto, C.A. (2017). Psychologically informed implementations of sugary-drink portion limits. Psychological Science, 28(5), 620-629.