To reduce added-sugar consumption, jurisdictions are considering requiring restaurant menu labels to identify high-added-sugar items. This study examined the impacts of added-sugar warning labels on hypothetical choices, knowledge of items’ added-sugar content, and perceptions of high-added-sugar items.

The design was an online RCT.

National sample of adults (N=15,496) was recruited to approximate the U.S. distribution of sex, age, race, ethnicity, and education.

Participants viewed fast-food and full-service restaurant menus displaying no warning labels (control) or icon-only added-sugar warning labels next to high-added-sugar items (containing >50% of the daily recommended limit).

The main outcome measures were hypothetical ordering of ≥1 high-added-sugar item, grams of added sugar ordered, and knowledge of items’ added-sugar content assessed in 2021 and analyzed in 2021–2022.

Warning labels reduced the relative probability of ordering ≥1 high-added-sugar item by 2.2% (probability ratio=0.978, 95% CI=0.964, 0.992; p=0.002); improved knowledge of added-sugar content (p<0.001); and led to a nonstatistically significant reduction of 1.5 grams of added sugar ordered, averaged across menus (p=0.07). The label modestly reduced the appeal of high-added-sugar items, increased perceptions that consuming such items often will increase Type 2 diabetes risk, increased perceived control over eating decisions, and increased injunctive norms about limiting consumption of high-added-sugar items (ps<0.001). However, in the warning condition, only 47% noticed nutrition labels, and 21% recalled seeing added-sugar labels. When restricting the warning condition to those who noticed the label, the result for grams of added sugar ordered was significant, with the warning condition ordering 4.9 fewer grams than the controls (95% CI= –7.3, –2.5; p<0.001).

Added-sugar warning labels reduced the probability of ordering a high-added-sugar menu item and increased participants' knowledge of whether items contained >50% of the daily value for added sugar. The modest magnitudes of effects may be due to low label noticeability. Menu warning labels should be designed for noticeability.

This study was registered at AsPredicted.org #65655