Comparison of National Dysphagia Diet and International Dysphasia Diet Standardization Initiative Levels for Thickened Drinks Prepared with a Commercial Xanthan Gum-Based Thickener Used for Patients with Dysphagia

The thickness levels of fluids for patients with dysphagia are established according to the guidelines of the National Dysphagia Diet (NDD) and International Dysphagia Diet Standardization Initiative (IDDSI). The nectar- (level 2), honey- (level 3), and pudding-like (level 4) fluids in NDD are consistent with the mildly (level 2), moderately (level 3), and extremely (level 4) thick fluids in IDDSI, respectively. In this study, NDD levels were compared with IDDSI levels by estimating both the apparent viscosity (ηa,50) and the residual volume (mL) in the IDDSI syringe flow test of thickened drinks prepared with a commercial xanthan gum-based thickener at different concentrations (0.1∼3.1%, w/w). The concentration range of the thickener in thickened drinks at each IDDSI and NDD level increased in the following order: water> orange juice> milk. A small difference was noted in the range of thickener concentration in the same NDD and IDDSI levels for thickened milk when compared with other thickened drinks. These results indicate that the thickener concentration ranges of thickened drinks for the classification of NDD levels differed from those of IDDSI levels, and they appeared to be greatly influenced by the type of drink. These findings could provide useful information for practically indicating the reliable thickness levels by the IDDSI flow test in clinical practice.