Front-of-package ultraprocessed warning labels: a randomized controlled trial with Chilean parents

Background Interest in ultraprocessed food (UPF) front-of-package labels (FOPLs) has been gaining momentum, but questions remain about their added value in the context of established nutrient-based FOPL systems. This study examined the impact of adding a UPF label to Chile's existing nutrient FOPLs on Chilean parents' product perceptions and behavioral intentions. Methods In 2025, Chilean parents (analytical sample n = 3,519) were randomly assigned to either a control condition (nutrient labels only) or a UPF label condition (nutrient labels plus UPF label). Participants viewed three similar products (all potato chips with the same flavor, all UPFs, one not high in any nutrients of concern, one high in one nutrient, and one high in two nutrients), indicated whether they believed each product to be ultraprocessed, and rated their product purchase intentions and perceived product healthfulness. Average differential effects (ADEs) are reported in percentage points (pp) or 1–5 scales. Results Compared to control, the addition of the UPF label improved participants' ability to correctly identify products as ultraprocessed, but effect sizes decreased as the number of nutrient labels increased (ADE = 12pp for product not high in nutrients of concern, ADE = 4pp for product high in one nutrient, both p < 0.001; p > 0.05 for product high in two nutrients). The addition of the UPF label also led to lower purchase intentions and perceived healthfulness for all three products, but effect sizes again decreased as the number of nutrient labels increased (purchase intentions: ADE = 0.32 for product not high in nutrients of concern, ADE = 0.23 for product high in one nutrient, ADE = 0.20 for product high in two nutrients; perceived healthfulness: ADE = 0.33 for product not high in nutrients of concern, ADE = 0.17 for product high in one nutrient, ADE = 0.11 for product high in two nutrients; all p < 0.001). Conclusions Overall, the addition of UPF labels to existing FOPL systems may help consumers more easily identify products as ultraprocessed and lower consumers' perceived healthfulness and purchase intentions of UPFs. UPF labels could have the largest effects when applied to UPFs that carry no or few nutrient labels. Registration https://clinicaltrials.gov/study/NCT06842680 .