"I jumped on board with IDDSI because I’ve always believed it would reduce errors in the food served to people."

John Holahan

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The Science Behind IDDSI Testing Methods

If you missed it live, IDDSI (the International Dysphagia Diet Standardisation Initiative) hosted a fabulous webinar earlier in June. The title was, “The Science Behind IDDSI Testing Methods”. Dr. Ben Hanson of University College London and IDDSI Board Member took the time to explain the science and the thinking behind the deceptively simple and easy, yet very powerful test methods used in the IDDSI Framework. You can read about the test methods on the IDDSI website here.


I’ve always enjoyed my conversations with Dr. Hanson and his practical understanding and approach to the needs of a caregiver as a meal is prepared and served. This compassionate and thoughtful approach led him and the IDDSI Board to develop very simple tests that define acceptable foods or drinks for each diet level within the IDDSI Framework. One of the most common critiques I hear about the IDDSI Framework is that the test methods are “not scientific” or are based upon opinion rather than science. In particular, people seem to want to dismiss the IDDSI Flow Test. I’ve written about this previously, but the IDDSI Flow Test has a remarkably strong correlation (0.90) to the results of a rheometer. Also, I know that gravimetric tests similar to the IDDSI Flow Test have been used for many years in various industries as a quality control device. Personally, I’ve always been drawn to simple solutions – especially because the tools are so readily available and inexpensive. And anything is better than the subjective judgments we’ve been using for too long.


While listening to Dr. Hanson’s presentation, I gained a new appreciation for the many factors that went into the selection of the particular 10 mL syringe used for the IDDSI Flow Test. The science has also been coming forward since the test was released to show how the apparently simple test is able to represent the wide range of conditions that go into a real swallow.


Dr. Hanson points out that a shear viscosity – like the methods suggested in the National Dysphagia Diet – is a measurement of thickness under one specific amount of force – the shear rate of 50 1/sec. But a human swallow actually involves a large number of shear rates acting upon a drink during the swallowing process. The IDDSI Flow Test produces a large variety of shear rates as the drink drains from the syringe. In this way, the force in the syringe is likely a better proxy of a swallow than would be from a single shear rate measurement.


The webinar was terrific, and anyone interested in the science and the thoughtful balancing of the needs of end-users will definitely enjoy this presentation. It is available on the IDDSI YouTube channel here.


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