Perceptions of processed foods as unhealthy: Heuristic strength, prevalence, and potential implications for the protein shift

•The “processed foods are unhealthy” heuristic was resilient to visual response bias.•The effect was prevalent and positively associated with food technology neophobia.•The impact of the heuristic on perceived healthiness differed across food categories.•Plants and fish were penalised more than meat for an increase in apparent processing.•Health perceptions largely aligned with Nutri-Score, but with notable exceptions.