Division 13, Swallowing and Swallowing Disorders (Dysphagia), has long recognized and supported the need to improve the standardization of dysphagia diets based on evidence-based research. The following articles provide more information about the National Dysphagia Diet (NDD), which has stimulated considerable interest and discussion among dietitians and speech-language pathologists. SLPs contributed to the development of the diet, but it was not officially reviewed or approved by ASHA.
-Paula A. Sullivan
Coordinator, Division 13, Swallowing and Swallowing Disorders (Dysphagia)
Diet texture modification for dysphagia management is a common practice, but one that is open to wide variation across clinicians and the facilities in which they work. Previous research has demonstrated that clinicians, including speech-language pathologists (SLPs), show significant variation in the amount of thickening powder they feel is necessary to mix a liquid to "nectar-thick" or "honey-thick" consistency.
The National Dysphagia Diet (NDD), published in 2002 by the American Dietetic Association, aims to establish standard terminology and practice applications of dietary texture modification in dysphagia management. While the publication of common terminology is long overdue, SLPs need to exercise caution when interpreting and applying the proposed terminology. As the NDD states, "Further study and peer-reviewed, scientific data will be needed to truly quantify the management parameters surrounding the complex diagnosis of dysphagia."
The NDD was developed through consensus by a panel of dietitians, SLPs, and a food scientist. It proposes the classification of foods according to eight textural properties, and anchor foods to represent points along continua for each property. A hierarchy of diet levels is then proposed, with inclusion and exclusion of items at each level based on subjective comparison with these anchor foods. There are four levels of semisolid/solid foods were proposed in the NDD:
- NDD Level 1: Dysphagia-Pureed (homogenous, very cohesive, pudding-like, requiring very little chewing ability).
- NDD Level 2: Dysphagia-Mechanical Altered (cohesive, moist, semisolid foods, requiring some chewing).
- NDD Level 3: Dysphagia-Advanced (soft foods that require more chewing ability).
- Regular (all foods allowed).
The NDD reports that over 100 different foods were analyzed using an instrumental texture analyzer. However, no data or explanation of the procedures and analysis that led to the "anchor" food scale has been provided in this first draft.
Four frequently used terms were chosen to label levels of liquid viscosity (i.e., thickness or resistance-to-flow) in the NDD; however, the NDD Task Force acknowledges that these ranges are "a commonsense approach" and "a catalyst for more research."
Proposed terms for liquids and correlating viscosity ranges:
1. Thin 1-50 centiPoise (cP)
2. Nectar-like 51-350 cP
3. Honey-like 351-1,750 cP
4. Spoon-thick >1,750 cP
The NDD further speculates that a severity outcome scale, such as the Dysphagia Outcome and Severity Scale (DOSS) may be useful to "describe a patient's dysphagia sufficiently to begin the diet prescription process for that patient." Given the lack of available evidence to support the practice of correlating the proposed dysphagia diet levels with available (but un-validated) severity scales like the DOSS, we believe usage of the NDD in this manner is ill-advised. Indeed, we suggest that customization of diet recommendations to meet patients' individual needs will always be preferable to a formulaic approach using classification schemes such as those recommended in the NDD.
There is clearly much work to be done before the current NDD tool can be employed to recommend clinically appropriate dysphagia diets for patients. Empirical research regarding the standardization of liquid viscosity and food textures is still in its infancy, and the NDD appropriately calls for evidenced-based research in this area. In the current version of the NDD, the authors have provided clinical researchers with a template upon which future scientific research can be initiated.