Online Randomized Controlled Trials of Restaurant Sodium Warning Labels

Policymakers are interested in requiring chain restaurants to display sodium warning labels on menus to reduce sodium consumption. This study examined the influence of label design on consumers' hypothetical choices, meal perceptions, and knowledge.

Four sequential, randomized, controlled online experiments were conducted.

Across all 4 experiments, 10,412 sociodemographically diverse participants were recruited online through Survey Sampling International and Amazon Mechanical Turk.

Participants were randomized to view restaurant menus with either no sodium label (control) or 1 of 13 sodium warning labels that varied the text (e.g., "sodium warning" versus "high sodium"), icons (e.g., stop sign), and colors (red/black) used. Participants placed a hypothetical meal order and rated restaurant meal perceptions. Data were collected and analyzed in 2016-2019.

The primary outcome was sodium content of hypothetical restaurant choices. Secondary outcomes included restaurant meal perceptions and sodium knowledge.

In Experiments 1-3, all warning labels reduced average sodium ordered across both restaurants (by 19-81 mg) versus controls, with some of the largest reductions from traffic light and stop sign labels, but results were not statistically significant. In a larger, preregistered replication (Experiment 4) testing traffic light and red stop sign labels versus control, traffic light and red stop sign labels significantly reduced average sodium ordered across both restaurants (-68 mg, p=0.002 and -46 mg, p=0.049, respectively). Warnings also significantly increased participants' knowledge of sodium content and perceived health risks associated with high-sodium meals compared with no label.

Traffic light and red stop sign warning labels significantly reduced sodium ordered compared with a control. Warning labels also increased knowledge about high sodium content in restaurant meals. Designs with warning text are likely to improve consumer understanding.