Impact of oral processing on liquid food viscosity: Clinical implications for dysphagia management

Background: The viscosity of liquid foods is a key factor in dysphagia management, as it influences swallowing safety and efficiency. Although it is typically assessed before ingestion, oral processing can modify it, potentially affecting clinical recommendations. Objective: To assess viscosity variations in commonly consumed liquid foods after oral processing and analyze their implications for dysphagia management. Methods: A cross-sectional observational study was conducted with 40 healthy volunteers, stratified by age and sex. Nine commercially available liquid products were selected and classified according to the National Dysphagia Diet (NDD). Each participant orally processed the products for 10 seconds, after which viscosity was measured using a Brookfield DV2T rotational viscometer. Changes in viscosity and NDD classification were analyzed using t-tests, factorial ANOVA, and chi-square tests. Results: All products exhibited a reduction in viscosity following oral processing, with greater decreases observed in those with higher initial viscosity. Seven out of nine products changed their NDD classification. No significant associations were found between viscosity changes and sex or age, except for two products (N2 and P1). Conclusion: Clinicians should reconsider exclusive reliance on extraoral viscosity measurements when prescribing liquid diets for individuals with dysphagia. Oral processing significantly modifies food viscosity, suggesting the need to adapt dietary prescriptions to reflect each person’s swallowing conditions better. Further studies are needed to integrate individual variability in oral processing.