Sugary Drink Labeling Study
Phase: NA
Conditions: Health Behavior
Sponsor: University of North Carolina, Chapel Hill

Complete Title: Sugary Drink Labeling Study 
Protocol Date: January 14, 2026 
NCT #: NCT07294053 
 
Study Principal Investigator:  
Marissa G. Hall 
University of North Carolina 
email: mghall@unc.edu 
 
 
  
 
 

Protocol Synopsis  
 
Study title 
Sugary Drink Labeling Study 
Funder 
National Institute of Diabetes and Digestive and Kidney Diseases 
Study rationale 
• 
Sugary drinks are a top source of added sugar in the United States 
• 
“High in added sugar” warnings have been implemented in 10+ 
countries, but it is unclear whether these warnings would affect 
sugary drink purchasing in the US 
Study objectives 
• 
Evaluate whether a “High in added sugar” warning label reduces 
added sugar purchased from sugary drinks compared to a control 
label. 
• 
Evaluate whether a “High in added sugar” warning label changes 
other secondary outcomes compared to a control label.  
Study design 
 
Randomized clinical trial 
Number of 
participants  
~543 participants 
Study duration 
Each participant is in the trial for ~3 weeks. The trial enrollment period is 
expected to last ~24 months. 
Study phases 
  
The trial will have two phases: 
(1) Screening: screening for eligibility and obtaining consent, and  
(2) Intervention: intervention/experimental treatment 
 
Study protocol 
This study aims to determine whether new added sugar warnings on sugary drinks lead to a 
lower amount of added sugar purchased from sugary drinks. We aim to enroll approximately 543 
adults ages 18 and older who have purchased at least one sugary drink from a store in the past 
week. Participants will attend 4 in-person study visits at our experimental store, spaced 
approximately 1 week apart. We will randomize participants to 1 of 2 trial arms at the time of 
scheduling. At the ﬁrst visit, participants will provide written informed consent. At each study visit, 
participants will shop for beverages in the store and take a computer survey. Participants will view 
sugary drinks in the store labeled per their trial arm. Researchers will record in-store purchases, 
and other self-reported measures will be assessed via the computer surveys. 
 
Statistical analysis plan 
 
Predictions 
For the primary outcome, we predict that the amount of added sugars purchased from sugary 
drinks will be lower in the added sugar warning arm compared to the control arm.  
For secondary outcomes, we predict that the amount of total sugars purchased from all 
beverages, volume of sugary drinks consumed in the past 7 days, and perceived healthfulness of 
sugary drinks will be lower in the added sugar warning arm compared to the control arm. We 
predict that intentions to reduce sugary drink consumption, forgoing sugary drinks, learning 
something new, correct identiﬁcation of beverages high in added sugar, and thinking about the 
harms of sugary drinks will be higher in the added sugar warning arm compared to the control arm.  
 

Statistical methods 
Analyses will be intent-to-treat, including all participants who attended Visit 1. Inferential tests 
will use a critical alpha of 0.05 or 95% conﬁdence intervals and two-tailed tests. 
We will descriptively present demographic characteristics separately for each trial arm. We will 
not conduct statistical balance tests that compare trial arms on demographic characteristics, 
following CONSORT guidelines for randomized clinical trials. For multi-item self-report measures 
completed by study participants, we will calculate the mean across individual items, assuming 
sufficient internal consistency reliability (Cronbach’s alpha >=0.60). If internal consistency is lower, 
we will consider dropping items or analyzing individual items as separate constructs.  
To examine the impact of trial arm on the primary outcome, we will use mixed-effects linear 
regression. The repeated measures outcome will be the amount of added sugars purchased from 
sugary drinks at each visit. The predictors will be trial arm (using the control arm as the reference 
group) and study visit (Visit 1, 2, 3, or 4). Analysis will treat the intercept as random.  
We will explore whether the impact of trial arm on the primary outcome differs by the following 
potential moderator variables: prior exposure to warning labels, diagnosis of a chronic disease, 
having limited English proﬁciency, volume of sugary drinks consumed in the past 7 days at baseline, 
and income. For each moderator, we will repeat the analyses, adding the variable and the 
interaction of the variable with trial arm as predictors. If the interaction term is signiﬁcant, we will 
report the impact of trial arm on the primary outcome at each level of the moderator. We will adjust 
p-values for probing moderation analyses for multiple post-hoc tests using a Bonferroni-Holm 
correction. 
Next, we will examine the impact of trial arm on secondary outcomes. We will use mixed-
effects linear and logistic regression for outcomes with repeated measures, using the same 
predictors as in the primary outcome model. For learning something new and correct identiﬁcation 
of beverages high in added sugar (binary outcomes assessed only once), we will use standard 
logistic regression. For volume of sugary drinks consumed in the past 7 days (continuous outcome 
assessed only once), we will use standard linear regression.  
 
Sample size needs  
To estimate sample size needs for analyses of the primary trial outcome, we assumed 4 
repeated measures, 2 trial arms of equal size, an intraclass correlation of .50, and 90% retention. 
An F-test for repeated measures was the statistical test chosen to compare the means of the 2 trial 
arms across 4 time points in G*Power. Alpha was set to .05 and power was set to .80. Based on 
previous studies examining the impact of labeling on behavior,1,2 we aim to detect a small effect 
size (d =.20). The results of the power calculation indicated a total sample size of 543 participants.  
 
 
References 
1. 
Hall MG, Grummon AH, Higgins ICA, et al. The impact of pictorial health warnings on 
purchases of sugary drinks for children: A randomized controlled trial. Plos Med. 2022. 
2. 
Grummon AH, Taillie LS, Golden SD, Hall MG, Ranney LM, Brewer NT. Sugar-sweetened 
beverage health warnings and purchases: A randomized controlled trial. Am J Prev Med. 
2019;57(5):601-610.