Food texture is a very important component of dysphagia. However, determining, describing and delivering the proper texture of foods and liquids has been a major source of frustration for everyone involved with the patient. The concern for proper hydration, nourishment and patient gratification must be balanced by caution over aspiration and choking. Often these latter two concerns receive the most emphasis, making hydration, nourishment and patient gratification hard to achieve.

Frequently the vocabulary used to describe the desired food texture is confusing or misunderstood. And the lack of standardization of the key food texture properties makes it difficult to communicate what the patients should have compared to what they actually get. How would you convey the properties of fresh bread vs. stale bread, or of canned peaches vs. fresh ripe peaches, without having the actual foods on hand? Most of us know it when we see it, but have difficulty adequately describing it to someone else. This is the dilemma faced daily by thousands of people who deal with dysphagia.

Fortunately, food science has the tools to deal with this problem. Some food scientists are trained to analyze and measure food texture. These specialists, known as food rheologists, use instruments to objectively measure the many properties of a food that contribute to its texture. For instance, viscosity can be determined using devices, called viscometers, that employ standardized and measurable forces to give reproducible read outs.

Although food rheology has not been extensively applied to dysphagia in the past, it has broad application. Recognizing this potential, the National Dysphagia Diet Task Force is defining the levels of diet in rheological terms. It is hoped that this will stimulate research to get a deeper understanding of the dysphagia/rheology interaction which should lead to a better products.

Food texture is the group of physical properties derived from the structure of the food that can be sensed by touch This touch is usually by the elements of the oral/pharyngeal cavities but may be sensed by other parts of the body, such as by the hands. It is not related to the chemical senses of taste or odor nor is it the sensation of temperature or pain. It is not normally a single property but rather a composite of many properties that varies with the particular food.

There are five basic forces involved with eating. These are:
1. Compression - The deforming of a food using force, such as between the tongue and palate.
2. Adhesiveness - The attraction between the food and an external surface, such as food sticking to the palate
3. Tensile - The extending of foods under force, such as the effects of the muscles on the bolus as it travels through the pharynx
4. Shear - The cutting of a food into pieces by forces that are not directly opposing, such as the lateral movement of the molars during chewing.
5. Fracture - The breaking of the food by two directly opposing forces, such as the incisors biting through a cookie.

These forces are used in varying degrees depending on the nature of the food and its position within the oral/pharyngeal/esophageal continuum. For instance, fracture occurs only with solid foods and mainly during the dentition stage. Adhesiveness could be a serious problem if part of the bolus adheres to the pyriform sinuses and is subsequently aspirated.

By observing how the patient handles various textures and then matching those textures to ‘real' foods, a menu can be tailored to that person's specific needs. This will help define the range of allowable foods and help health care professionals communicate with each other and with other care givers.

In summary, food rheology can play an important part in the treatment of dysphagia by objectively characterizing the properties of the foods most acceptable to a patient and aiding in the selection of foods that fit the prescription.

Future articles will cover how the use of texture measurement can help the health care professional better diagnose, treat and nourish the dysphagic patient.