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192 CLINICAL MANAGEMENT OF SWALLOWING DISORDERS
TABLE 8–2. Rheology Terminology
Creep test A test to determine the deformation of a material exposed to a constant stress.
These are like relaxation tests, but a constant stress is applied, rather than a
constant strain. The simplest creep test would be to apply a weight on top of a
sample and record the change in shape (strain) over time; for example, placing a
book on a cake and measuring the deformation over time.
Density The compactness of a substance; the ratio of its mass to its volume measured in
grams per milliliter (g/mL) or kilograms per milliliter (kg/mL).
Homogeneous Well mixed and compositionally similar regardless of location.
Incompressible Material that shows no change in density when a constant stress is applied
(eg, water).
Isotropic The material response is not a function of location or direction.
Kinematic viscosity Viscosity divided by the density of the material.
Laminar flow Nonturbulent flow.
Linear viscoelasticity Viscoelasticity within the region where stress and strain are linearly related.
Newtonian fluid A fluid with a linear relationship between shear stress and shear rate with a yield
stress. The fluid viscosity of a Newtonian fluid does not vary with shear rate.
Non-Newtonian fluid Any fluid deviating from Newtonian behavior (eg, fluids that are suspensions). The
attractive force between suspended particles weakens as shear rate increases.
Rheogram A graph showing rheological relationships.
Rheometer An instrument used for measuring rheological properties. This device is used in
creep tests.
Shear (strain) rate Change in strain with respect to time.
Strain Relative deformation.
Viscoelastic A material having both viscous and elastic properties.
Viscosity Resistance to flow or alteration of shape by a substance as a result of molecular
cohesion. This is perhaps the most important property when planning a diet for
someone with a swallowing disorder. Newton’s postulate reasons that if the
shear stress is doubled, the velocity gradient (shear strain rate) within the fluid
is doubled. For fluids, strain is measured in terms of shear rate, and the shear
stress may be expressed as some function of shear rate and viscosity. For
Newtonian fluids, the viscosity function is constant and called the coefficient of
viscosity or Newtonian viscosity.
Viscometer A device used to measure the resistance of a material to flowing.
Applications of Rheology
Viscosity is a prime variable in the study of Newtonian fluids. For simplicity, the clinician may view
the viscosity of a fluid as being proportional to the
force required to move it through. A bolus that is
twice as viscous requires roughly twice as much
power from the swallow musculature to transport
the bolus. Viscosity sheer rate profiles for different
types of fluids can be found in the literature.
5–7
Density also plays a role in the analysis of liq-
uids. Density can be affected by temperature and
8. NUTRITION AND DIETS 193
the thickening agent. As the compactness of a substance changes, its flow will also change. Thus, the
density may decrease as the compactness decreases.
Moreover, if a product stays in the oral cavity for any
length of time, its denseness may change, leading to
misinterpretation of the type of fluid a patient can
or cannot swallow.
ORAL NUTRITION AND DYSPHAGIA DIETS
Oral nutrition is often the goal for most patients
with dysphagia due to stroke or for those who have
undergone head and neck cancer surgery. Conversely, for patients with progressive neuromuscular
diseases, oral nutrition may be the starting level of
intervention, with progression to an enteral feeding
stage due to the progress of the disease.
Oral nutrition diets are organized on the basis
of viscosity of the foods and liquids. Safe swallowing requires temporal management of the neuromuscular behaviors at each stage of the swallow.
able in multiple languages and being adopted by
multiple countries. The American Speech-LanguageHearing Association and the Academy of Nutrition
and Dietetics officially launched implementation
of the IDDSI in the United States from May 2019.
Australia, Canada, New Zealand, and many other
countries have also started implementing or are
in the progress of implementing the IDDSI framework within their health systems. For updated
information about IDDSI, please refer to the IDDSI
official website.
IDDSI — Food Description can be found by scanning
the accompanying QR code.
Drinks: According to the IDDSI framework,
there are 5 levels of drinks (Table 8–3):
Thin (level 0): eg, Clear liquids, milk, coffee
and tea, and broth-based soups
Slightly thick (level 1): eg, “antiregurgitation”
infant formula
Mildly thick (level 2): eg, honey, nectar
All dysphagia diets should adjust food/liquid
intake for (1) amount, (2) viscosity, (3) consistency,
and (4) timing of the meal to achieve maximal
nutrition and maintenance of the desired
viscosity over the course of the feeding period.
Diets and Consistencies
The management of oral feeding requires an understanding of liquid viscosities and food textures. The
International Dysphagia Diet Standardisation
Initiative (IDDSI) proposed 8 levels to describe
foods and drinks of different viscosity and texture.
The use of standardized terminologies across settings and countries will allow ease of communication across institutions and comparisons across
studies and will gather more evidence for the use of
diet modifications as a dysphagia treatment option.
Figure 8–1 shows the 8 levels of foods and drinks
proposed by the IDDSI. Currently IDDSI is avail-
Moderately thick (level 3): eg, smoothie
Extremely thick (level 4): eg, puree
Liquid modification may be used to increase
or decrease the viscosity of the liquid to achieve
bolus control. Thin or thick liquids may require
thickening agents to modify the consistency. It
should be remembered that these thickeners may
also alter other aspects of the bolus, such as cohesiveness, taste, appearance, and flow. A number
of food thickeners are now available in supermarkets, pharmacies, and health food stores. Table 8–4
lists some common thickening agents that may be
used. Because new products are being developed
and marketed constantly, it is not the purpose of
this chapter to recommend one manufacturer over
another. Rather, clinicians will have to keep up with
new materials and with the modifications that companies offer. The amounts to be mixed will vary
substantially, and the clinician may resort to “trialand-error” mixture consistency for each individual.
The key is to clearly document how to prepare the
final consistency that suits each individual.
194 CLINICAL MANAGEMENT OF SWALLOWING DISORDERS
FIGURE 8–1. International Dysphagia Diet Standardisation Initiative (from https://www
.iddsi .org). The IDDSI Framework and Descriptors are licensed under the Creative Commons Attribution Sharealike 4.0 License.
TABLE 8–3. Descriptors of the International Dysphagia Diet Standardization Initiative (IDDSI) Liquid Levels
Liquid Level Examples Suggested Target Population IDDSI Flow Test
0 (Thin) • Water
• Apple juice
1 (Slightly thick) • Antiregurgitation
(AR) infant formula
• Buttermilk
2 (Mildly thick) • Gravy
• Yogurt drinks
3 (Moderately thick) • Molasses
• Yogurt
4 (Extremely thick) • Pureed fruits
• Avocado spread
• For individuals who can
safely swallow all levels of
liquids
• Mainly used in the pediatric
population as a thickened
drink
• Individuals who have slightly
reduced tongue control
• More reduced tongue and
oral control than level 2
• Poor tongue control
• Increased risk of residue
• Flows through
completely in 10 s
• Leaves 1–4 mL in the
syringe after 10 s
• Leaves 4–8 mL in the
syringe after 10 s
• Leaves >8 mL in the
syringe after 10 s
• No flow or drop
through after 10 s
8. NUTRITION AND DIETS 19 5
TABLE 8–4. Common Agents for Modifying the Viscosity of Food and Drinks
Noncommercial Agents
Thinning Agents/Blenderizing Agents Thickening Agents
Milk
Gravy
Juice
Commercial Thickening Agents
Company
Nestle Health Science
https://www.nestlehealthscience.com/
brands/thickenup
Thick-It
http://www.thickit.com
Simply Thick
http://www.simplythick.com
Hormel Health Labs (Thick & Easy)
http://www.hormelhealthlabs.com
Nutricia Nutilis
https://www.nutricia.com/products/
stroke-and-dysphagia/nutilis-clear.html
Cornstarch
Baby cereal (or other dehydrated baby food)
Mashed potato flakes
Instant pudding
Unflavored gelatin
Ready-to-Consume
Products Product Basis
3
3
X Xanthan gum
3
3
Modified cornstarch
and xanthan gum
Modified cornstarch
and xanthan gum
Starch and gum based
Starch and xanthan
gum
Flavour Creations
https://www.flavourcreations.com.au
The current commercially available thickeners
or prethickened beverages vary in their thickening
ingredients. They may be starch based, xanthan gum
based, or a mixture of both. Table 8–5 lists the different types of thickeners that may be used to alter
the viscosity of fluids. When choosing which type
of thickeners to use, dietitians and pharmacists may
also be consulted on possible interactions with other
chronic diseases (such as diabetes) and medications.
Where possible, clinicians can arrange for a
“thickener-tasting” session to let the patients
choose the products they prefer to use.
3
Xanthan gum
Although there has been a significant increase
in the number of thickeners available, there remains
a need to identify the rheological properties as they
relate to viscosity, because viscosity plays a major
role in the consistency of the fluid swallowed.
There is no clear evidence from the literature
that suggests which viscosity levels should be used
for different levels of dysphagia severity. In general, studies showed that thicker fluids flowed more
slowly down the swallowing tract and increased the
duration of the swallowing events
8–12
than thin fluids. Thicker fluids and harder foods were reported to
require greater tongue, jaw, pharyngeal, and laryngeal efforts to swallow.
10,13–16
When focusing on dys-
phagic patients, studies showed that thicker fluids
196 CLINICAL MANAGEMENT OF SWALLOWING DISORDERS
TABLE 8–5. A Comparison of Commercially Available Liquid Thickeners
Gum-Based
Thickeners (with
starch powder
ingredients) Gel Thickener
• Remain clear
• Smooth slightly
slippery texture
Mixed in any
beverage
Appearance
when added to
clear beverage
Consistency
changes over
time
Starch-Based
Thickeners
(powders)
Ye s Ye s Ye s • Ready-to-drink • Only with water
• Appear cloudy
• Slightly grainy
texture
Ye s No No No Ye s
reduced the amount of penetration and aspiration
but at the same time increased the amount of postswallow pharyngeal or vallecular residue.
10-12,17–19
The key to recommending thickened fluids as
a treatment option is to find a consistency that
allows maximal protection from penetration and
aspiration but, at the same time, a minimal level
of postswallow residue.
The decision to use which viscosity level is
often made after studying the swallow patterns with
the MBS or FEES. Clinicians should note the type
and consistency of the barium and thickeners used
during testing. Where regular MBS studies are done,
premixed barium consistencies should be available
to the clinician so that when a report is generated,
the treatment team will know the conditions under
which the patient was evaluated. An instrumental
assessment of swallowing provides an indication of
acceptable viscosities for maximum safe swallowing once it has been shown that the patient has
adequate sensation. It is important that the entire
team understands the viscosities and uses consistent
mixtures during the treatment.
When clinicians are using premixed barium
products or ready-to-drink thickened fluids, they
should be aware that the viscosity of these prod-
Prethickened
Drink Mixes
(starch powder
based)
• Appear cloudy
• Slightly grainy
texture
• Remain clear
• Smooth slightly
slippery texture
Prethickened
Beverages
(starch or gum
based)
• Clarity depends
on type of
thickener used
ucts might vary from brand to brand even when
they are labeled to be representing the same level
of fluid thickness.
For drinks that are thickened using starch-based
thickeners, the consistency may change over
time and when the drinks are mixed with saliva.
When a patient retains foods or drinks in the oral
cavity for lengthy periods of time, the viscosity
and density are no longer the same as when the
foods or drinks were prepared.
Speech-language pathologists may perform
their own flow test on products that they will use in
instrumental assessment and in treatment to ensure
the appropriate fluid thickening level is recorded for
communication among the dysphagia team and for
future treatment planning. The IDDSI proposed a
simple 10-second flow test for fluids using an IDDSI
funnel. The results of the flow test for each fluid
level in the IDDSI framework are clearly listed in
their guidelines.
IDDSI — Drinks Description can be found by scanning the accompanying QR code.
YouTube Video — IDDSI Syringe Test Instructions can
be found by scanning the accompanying QR code.
8. NUTRITION AND DIETS 197
Liquid modifications often involve the preparation of the thickened drinks by the health care team
member responsible for the dietary consistency. Ideally, a liquid should be thickened to the consistency
as recommended by the speech-language pathologist. Most manufacturers list the mixing instructions
on their thickening products.
It is important that speech-language pathologists provide clear and simple written guidelines
on food and drink preparation to family members
or health care providers who are responsible for
daily preparation of meals and drinks. Regular
training and monitoring of diet modifications
should also be conducted.
IDDSI published a series of patient handouts specific for each IDDSI level. The resources can be
freely downloaded from the IDDSI website.
Foods
Texture refers to the composition of foods. The goal
of normal swallowing is oral intake of all foods,
liquids, as well as solids. The intake of solid foods
is related to the severity of impairment, adequate
dentition for chewing, and muscular strength and
coordination for bolus transit and control. According to Bourne,
ing food texture. These characteristics and examples
of the textures related to these characteristics are
shown in Table 8–6.
Texture modifications: According to the IDD-
SI’s framework, there are 5 levels of foods:
Liquidized (level 3): Food is blended with
added liquid as needed to form a smooth,
moderately thick fluid.
Pureed (level 4): Food is blended with added
liquid as needed to form a smooth, extremely
thick fluid.
27
there are 5 characteristics for defin-
27,28
An additional issue associated with thickened
liquids is the risk of dehydration because of reduction in fluid intake, especially in the older adult
populations.
20–22
Limited access to thickened liquids,
change in taste and texture, and inability to quench
thirst are some of the factors that may be associated
with poor intake of thickened liquids. With the aim
to improve hydration level, a rehabilitation hospital
proposed a Frazier Water Protocol (or also known
as Free Water Protocol).
23
The protocol proposes
that free water access is given to patients who are
on thickened liquids and nonoral diets. The protocol clearly specified when and how thin water
may be given and cases where this protocol would
not be recommended. Recent studies have found
that patients who were mobile and had good cognitive functions benefited from this water protocol in
terms of increased level of hydration and improved
quality of life without increasing the risks of aspiration pneumonia.
24–26
If the free water protocol is
recommended, it is crucial that the SLP and other
members of the dysphagia team review the protocol guidelines thoroughly to avoid misuse of the
protocol.
Minced and moist (level 5): An example is
finely mashed or minced tender meat that is
served with a thick smooth sauce that is mixed
with the foods.
Soft and bite sized (level 6): Examples include
naturally soft foods that require a minimal
amount of chewing, minced cooked tender
meats with no bones, or small pieces of
vegetables that are steamed or boiled.
Regular (level 7) or Easy to Chew (level 7EC):
This consists of daily foods of different textures
or daily foods of soft or tender textures.
When preparing pureed food, it is best to blend
each type of food separately (meat, vegetables,
grains) to maintain taste and color of food.
Shaping and molding may further improve the
presentation of the food.
Little evidence is available in the literature in
relation to the effect of texture modifications to
198 CLINICAL MANAGEMENT OF SWALLOWING DISORDERS
TABLE 8–6. Characteristics of Food Textures as Outlined by Bourne27
and the 8 Most Common Textures That Have a Significant Role in
Dysphagia Diets, According to the American Dietetic Association
Characteristics of Food Texture
1. It is a group of physical properties that derive from the structure
of the food.
2. It consists of a group of properties, not a single property.
3. It is sensed by touch, usually in the mouth but hands may also
be used.
4. It is not related to chemical senses of taste or odor.
5. It can be measured objectively by means of mass, distance,
and time.
Eight Textures Most Significant in Dysphagia Diets and
Treatments
1. Adhesiveness — The work required to overcome the attractive
forces between the surface of a food and another surface to
which it has contact (eg, amount of work required to remove
peanut butter from the palate)
2. Cohesiveness — The degree to which the food deforms (eg,
when a moist bolus of cracker is compressed between tongue
and palate)
3. Firmness — The force required to compress a semisolid food
(eg, compressing pudding between the tongue and palate)
4. Fracturability (“Biteability”) — The force that causes a solid food
to break (eg, biting peanut brittle with the incisors)
5. Hardness — The force required to compress a solid food to
attain a certain deformation (eg, chewing a hot dog just prior to
when it begins to shear)
6. Springiness — The degree or rate that a sample returns to its
original shape after being compressed (eg, marshmallows)
7. Viscosity — The rate of flow per unit force (eg, the rate at which
a milkshake or nectar is drawn through a straw)
8. Yield Stress — The minimum amount of shear stress that must
be applied to food before it begins to flow (eg, force required to
get ketchup to flow from a bottle)
a
Adapted from National Dysphagia Diet Task Force.
a
28
improve swallow safety. Studies have shown that it
takes longer and larger force to chew and swallow
harder solid foods.
29–32
Given the lack of evidencebased guidelines on texture modifications, clinicians
should carefully assess each individual’s responses
to different types of texture modifications and
clearly explain to the patients and caregivers the
rationale for the diet modifications and the preparation methods (Table 8–7).
Foods and drinks may behave differently in
persons with different tongue force, range of
movement, and amount of saliva. Clinicians
should carefully explore a range of food and
drinks with different levels of modifications that
are specific to the individual’s preference, needs,
and culture.
8. NUTRITION AND DIETS 19 9
TABLE 8–7. Description of Different Levels of Food Preparation According to International Dysphagia Diet
Standardization Initiative (IDDSI)
Food Level Examples Characteristics IDDSI Fork Pressure Test
3 (moderately
thick liquidized)
4 (pureed
extremely thick)
• Thick pumpkin soup
• Thick gravy and sauces
• Mashed potato
• Greek yogurt
• Clotted cream
5 (minced and
moist)
• Finely chopped or
minced meat served in
extremely thick, smooth,
nonpouring gravy
• Mashed fruits with
excess juices drained
• Thick and smooth cereal
with 2–4-mm lumps,
with excess milk or fluid
drained
6 (soft) • Cooked, tender meat
served in sizes of 1.5 cm
× 1.5 cm
• Casseroles, stews, and
curries containing small
solid pieces that are
soft and tender, no hard
lumps
• Steamed or boiled
vegetables in final
cooked size of 1.5 cm ×
1.5 cm
• Increased time for oral
control
• Alleviates pain on
swallowing
• Suitable for those with
significantly reduced tongue
control and those with no
teeth/denture issues (no
biting or chewing required)
• Alleviates pain on chewing
or swallowing
• Beware of residue
• Requires some tongue force
• Suitable for those with
missing teeth or denture
issues as biting is not
required
• Requires minimal chewing
• Tongue force required to
move the bolus
• Alleviates/prevents pain or
fatigue from chewing
• Requires adequate
tongue force for oral and
oral-pharyngeal stage
processing
• Suitable for those with
missing teeth or poorly fitted
dentures as no biting is
required
• Requires chewing
• Prevents pain or fatigue on
chewing
IDDSI flow test:
• leaving >8 mL in the
syringe after 10 s
• A clear pattern on the
surface
• The food retains the
indentation from the fork
• No lumps
• The particles should easily
be separated between and
come through the prongs
of a fork
• Can be easily mashed with
little pressure from a fork
• Pressure from a fork held
on its side can be used to
“cut” or break this texture
into smaller pieces
• When a sample is pressed
with the base of a fork,
the sample squashes
and changes shape, and
it does not return to its
original shape when the
fork is removed
7 (easy to
chew)
• Normal, everyday foods
of soft/tender textures
• Any method may be
used to eat these foods
7 (regular) • Normal, everyday foods
of various textures
• Any method may be
used to eat these foods
• Requires ability to bite soft
foods and chew
• Does not necessarily
require teeth
• Requires good chewing and
tongue control
• Suitable for those with
adequate swallow safety
• Same as for level 6
(except no restrictions on
sample size)
N/A
200 CLINICAL MANAGEMENT OF SWALLOWING DISORDERS
Table 8–8 presents 3 categories of foods that
are not well tolerated by individuals with swallowing problems.
Dysphagia Diet Guidelines
Different organizations around the world have
issued descriptions of different types or levels of
dysphagia diet as clinical guidelines before IDDSI
was developed. Table 8–9
these. These guidelines have been used regionally
to allow communication across organizations and
dysphagia team members. Some of these guidelines
may be fading out and being replaced by IDDSI.
National Dysphagia Diet—United States
Dysphagia diets vary considerably from facility to
facility. Although many hospitals, clinics, and nursing homes are beginning to adopt many of the
recommendations and features of the NDD,
siderable variation for specific patients remains. The
33–36
highlights some of
28
con-
NDD requires both the specification of food consistency and its viscosity. Traditional oral dysphagia diets are typically a stepwise progression to the
normal diet in 4 levels, and liquids are described as
4 levels of viscosity/consistency boluses.
Dysphagia Diet Food Texture
Descriptors—United Kingdom
The Descriptors37 were developed by the National
Patient Safety Agency Dysphagia Expert Reference
Group in 2011. The descriptors cover food texture,
but not for fluids. There are 4 levels of texture modifications. The guidelines provided detailed descriptions on how to prepare different types of food for
each level of modification.
Australian Standardized Definitions and
Terminology for Texture-Modified
Foods and Fluids
The Australian foods and fluids35 scales were consensus standards adopted by Speech Pathology Aus-
TABLE 8–8. Three Categories of Foods That Are Not Well
Tolerated by Individuals With Swallowing Problems
Crumbly and Noncohesive Foods
Plain ground meat, chicken, or fish
Scrambled eggs
Jello
Crackers
Peas, corn, or legumes
Mixed Consistency Foods
Vegetable soup
Soup with large pieces or chunks of food
Cold cereal with milk
Citrus fruit
Sticky Foods
Dry mashed potatoes
Peanut butter
Fresh white or refined wheat bread
Fudge or butterscotch sauce/caramel
Bagels or soft rolls
Cornbread
Cottage cheese
Coconut
Nuts and seeds
Salad with dressing
Canned fruit
Gelatin with fruit
Yogurt with fruit
8. NUTRITION AND DIETS 201
TABLE 8–9. International Guidelines on Dysphagia Diet
Name Country Levels of Diet Levels of Liquid
The National
Dysphagia Diet (NDD)
Dysphagia Diet Food
Texture Descriptors
The Australian Clinical
Food Texture Grading
Scale; The Australian
Clinical Fluid Texture
Grading Scale
Irish Consistency
Descriptors for
Modified Fluids and
Food (Based on the
Australian Scales)
a
Adapted from McCullough et al33; National Patient Safety Agency34; Atherton et al35; and IASLT.
United States • Dysphagia Pureed (NDD 1)
• Dysphagia Mechanically Altered (NDD
2)
• Dysphagia advanced (NDD 3)
United Kingdom • Thin Puree Dysphagia Diet (B)
• Thick Puree Dysphagia Diet (C)
• Pre-mashed Dysphagia Diet (D)
• Fork Mashable Dysphagia Diet (E)
Australia • Texture A (Soft): soft foods, moist or
served with a sauce
• Texture B (Minced and Moist): soft and
moist, easily forms into a ball
• Texture C (Smooth Pureed): smooth
and lump free
Ireland • Texture A (Soft): soft foods, moist or
served with a sauce
• Texture B (Minced and Moist): soft and
moist, easily forms into a ball
• Texture C (Smooth Pureed): smooth
and lump free
• Texture D (Liquidized): smooth,
pouring, uniform consistency, lump free
a
• Spoon-thick
• Honey-like
• Nectar-like
• Thin: includes all beverages
• Extremely thick (pudding/
stage 3)
• Moderately thick (honey/
stage 2)
• Mildly thick (nectar/stage 1)
• Level 150 (mildly thick)
• Level 400 (moderately thick)
• Level 900 (extremely thick)
• Grade 1 (very mildly thick)
• Grade 2 (mildly thick)
• Grade 3 (moderately thick)
• Grade 4 (extremely thick)
36
tralia and the Dietitians Association of Australia. The
scales include a regular food texture, 3 levels of
modified food textures, a level of regular fluid consistency, and 3 levels of thickened fluids. Descriptions of each level were provided, together with
food and drink examples.
NONORAL DIETS
Introduction
Some patients are unable to take adequate nutrition orally. This may be temporary in patients who
have had surgery for oral, pharyngeal, or laryngeal
disease or patients who are acutely recovering from
a stroke. It may be a long-term solution for some
patients, for example for those patients with a neuromuscular degenerative disorder who no longer
can manage oral nutrition.
Enteral feeding is a type of feeding that occurs
by way of the stomach or intestine. In patients who
are unable to take adequate nutrition by mouth but
otherwise have a functioning gastrointestinal (GI)
tract, this type of feeding can be used. The enteral
approach may reach the stomach, duodenum, or
jejunum via a feeding tube placed through the nose
or directly to the GI tract. Parenteral feeding (intravenous nutrition) is a type of feeding that bypasses
the GI tract and directly injects the nutrition into the
body through the veins. A special liquid mixture that
contains proteins, carbohydrates, fats, vitamins, and