What is food viscosity and how is it used in the treatment of dysphagia?

Updated: Mar 20, 2020
  • Author: Nam-Jong Paik, MD, PhD; Chief Editor: Elizabeth A Moberg-Wolff, MD  more...
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Food viscosity is defined as frictional resistance to shear. Food texture is defined as the group of physical properties derived from the structure of the food that can be sensed by touch. Touch usually is performed by elements of the oral and pharyngeal cavities. Food and liquid textures play important roles in the care of patients with dysphagia.

If oral feedings are determined to be appropriate, the viscosity and texture of the food should be considered, because patients vary in their ability to swallow thin and thick liquids. Liquids can be thickened with various thickening agents. Many commercially available, starch-based food thickeners are used to increase the consistency of food, and prethickened water, juice, coffee, and other products are available.

A uniform and viscous bolus of food or beverage enables a patient with a delayed swallow reflex to control mastication and transport. It also allows the individual to swallow with less risk of aspirating residue material, because there is a reduced tendency for the material to fall over the base of the tongue before the swallow mechanism is triggered. Viscosity also influences the swallowing reflex and peristaltic activity.

Viscosity of the diet for dysphagia is frequently described in a nonobjective manner. For example, tomato juice, nectar, honey, and pudding have been referred to as fluids.

Viscosity can be objectively determined by using a device called a viscometer. Another objective method of determining viscosity is a line-spread test. [53, 54] In this, diluted mix is placed on a circle marked on a glass plate and is allowed to stream for 5 minutes. Lengths of the 4 stream directions are measured, and their mean is determined.

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