Consumers can be helped by nutrition labels and ecolabels to make healthier and more environmentally friendly decisions. However, there is no data on how ecolabels perform in the context of nutrition labelling. This study's primary objectives were to determine whether ecolabels are helpful at encouraging sustainable purchasing behaviour when provided alongside nutrition labels, and whether nutrition labels are effective at encouraging healthy purchasing when presented alongside ecolabels. Participants (N=2730) were randomly assigned to view products with environmental effect labels only, nutrition (NutriScore) labels only, both environmental and nutrition labels, or (4) no labels when they visited an experimental online supermarket platform. The mean environmental impact ratings (EIS; primary outcome) and health scores of the items in participants' shopping carts were compared across conditions using linear regressions. When environmental impact labels were provided alone (1.3, 95%CI: 2.3 to 0.4) or with nutrition labels (2.0, 95%CI: 2.9 to 1.0), there were substantial decreases in the EIS compared to the control (no labels), with no indication that either of these two circumstances was more successful. Both when nutrition labels were exhibited alone and when ecolabels were also present, there was no evidence that nutrition labels had any effect on the EIS or the healthiness of purchases. When combined with nutrition labels or used alone, environmental impact labels may be useful at promoting more environmentally friendly purchases. This strengthens the body of research on the viability and efficacy of environmental impact labelling as a key strategy to alter eating habits and enhance global health.
