The Relationship Between Taste, Olfaction, and Nutrition in the Cancer Population

The Relationship Between Taste, Olfaction, and Nutrition in the Cancer Population
f u r t h e r r e f l e c t i O n S
The Relationship Between
Taste, Olfaction, and Nutrition
in the Cancer Population
Mark N. Farmer, MD, Ryan S. Raddin, MD, and John D. Roberts, MD
M
arising from specialized taste receptor cells lo-
cated on the tongue and oropharnyx.11
the sense of taste originates within the special-
ized epithelium lining the tongue’s edges and an-
tices and
alnutrition is a frequently encoun-
tered problem in cancer patients1 and
Dr. farmer is a Senior
a consistently poor prognostic indica-
fellow in Medical
tor.2–4 By implication, nutritional prac-
Oncology at the Medical
college of Virginia,
the nutritional management of patients
terior dorsal surface, the soft palate, and portions
richmond.
with cancer have a potentially significant impact
of the pharynx and larynx. Within this epithelium
Dr. roberts is the
on patient outcomes.5
are taste receptor cells that synapse with sensory
interim chair of the
Good nutritional practices (consuming ad-
axons carrying sensory information to the brain.
Division of hematology,
Oncology and Palliative
equate nutrients within caloric needs; maintain-
the lifespan of each taste receptor cell is short,
care at the Virginia
ing a healthy body weight; consuming a variety
lasting an average of 10 days; these cells are con-
commonwealth
of fruits, vegetables, whole grains, and low-fat
tinuously regenerated by nearby stem cells.12 the
university health
dairy products daily; minimizing trans-fatty acid
receptor cells are located in multicellular clus-
System, richmond,
Virginia
consumption; and decreasing consumption of
ters (“taste buds”). On the surface of the tongue,
Dr. raddin is a Senior
sodium-rich foods) can reduce or ameliorate the
these taste buds lie within three types of papillae:
resident in internal
“nutrition impact symptoms” that tend to impede
fungiform papillae are mushroom shaped and cover
Medicine at the
Medicine at the the
oral intake (eg, gastrointestinal disturbances, dys-
the anterior two thirds of the tongue; foliate papil-
Virginia commonwealth
phagia, sensory changes) and are associated with
lae are located on the posterolateral edges of the
university health
improved quality of life.6 Poor nutritional practic-
tongue, with taste buds tucked inside their folds;
System, richmond,
es, in contrast, are associated with poorer patient
and circumvallate papillae are large and form an arc
Virginia
outcomes, primarily resulting from an increased
on the posterior aspect of the tongue, with taste
incidence and severity of side effects, as well as an
buds lying in their surrounding moats.12
increased incidence of infection.7,8
Minor salivary glands known as von ebner’s
Of major importance to a patient’s nutritional
glands are located within the surrounding epithe-
status is his or her chemosensory function, partic-
lium, producing a serous secretion that fill the folds
ularly the senses of taste and smell.9,10 this article
of the papillae and dissolves taste molecules. Above
will review the biology of these two senses in the
each taste bud is a taste pore, a small opening in the
context of both health and neoplastic disease.
epithelium that restricts the flow of solute reaching
the taste receptor cells to small ions.12
Biology of Gustation
the apical end of each receptor cell contains
the so-called chemical senses of taste (or,
microvilli that are exposed to the oral mucus. lo-
more formally, gustation) and smell (olfaction)
cated on the microvilli are taste receptor proteins
are thought to be the oldest, or most primitive,
that allow us to distinguish between four basic
senses. in common parlance, “taste” often is
tastes: sweet, sour, salty, and bitter. (Some au-
used interchangeably with “flavor,” the fusion
thorities endorse a fifth taste, called umami, that
of taste and smell. in the physiologic sense,
serves to enhance the “savory” qualities of certain
“taste” is a term applied strictly to sensations
foods. it is believed that dysfunction in this taste
may be responsive to treatment with amino acid
correspondence to: Mark n. farmer, MD, 301 Virginia Street,
#1612, richmond, VA 23219; telephone: (434) 825-1234;
supplementation.13) Sweet and bitter chemicals
fax: (804) 828-5941; e-mail: oledocfarmer@msn.com
are detected by G-protein–coupled receptor fami-
J Support Oncol 2009;7:70–72
© 2009 Elsevier Inc. All rights reserved.
lies. Salty and sour chemicals are detected by ion-
70
www.SupportiveOncology.net
The Journal of SupporTive oncology

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Farmer/Raddin/Roberts
channel (na+, h+) receptors. Different combinations of these
to enter the cell. the resulting depolarization of the cell trig-
taste receptor proteins in individual receptor cells result in
gers action potentials. the signal is terminated as the increas-
varying degrees of sensitivity and specificity to different tastes.
ing intracellular levels of ca2+ and cAMP lead to activation of
Activation of these receptor proteins leads to depolarization of
protein kinases, which, in turn, inactivate the ion channels.12
the receptor cell, which, in turn, can interact with neighboring
Basally, the action potentials travel through slow unmy-
cells or release neurotransmitters to activate nearby neurons
elinated axons that extend in fascicles through the cribriform
located within the taste buds.12
plate to the paired olfactory bulbs.15 Within the bulbs, the ax-
the neural fibers located within the taste buds make up
ons synapse with mitral and tufted cells by releasing the neu-
parts of cranial nerves Vii, Xi, and X. the anterior two thirds
rotransmitter glutamate. these second-order neurons then
of the tongue are innervated by the chorda tympani nerve, and
project ipsilaterally to form the bilateral olfactory tracts that
the soft palate is innervated by the greater superficial petrosal
lie in the olfactory sulci of the basal forebrain.12 they convey
nerve, both of which are branches of the facial nerve (cranial
olfactory information to multiple areas of the central nervous
nerve Vii). the posterior third of the tongue is innervated by
system that, together, comprise the primary olfactory cor-
the glossopharyngeal nerve (cranial nerve Xi), and the phar-
tex. these areas consist primarily of the piriform cortex, the
ynx and larynx are innervated by the vagus nerve (cranial
amygdala, and the rostral entorhinal cortex.12,15 from the pri-
nerve X).12,14 these first-order neurons project ipsilaterally to
mary olfactory cortex, higher-order projections extend to form
synapses in the nucleus of the solitary tract within the brain
a complex web of connections with other areas of the brain,
stem.12,14,15 Second-order neurons travel through the thalamus
including the orbitofrontal cortex, thalamus, hypothalamus,
and project primarily to the insular cortex and the operculum,
basal ganglia, and hippocampus,12 all of which act together to
with other areas, such as the orbitofrontal cortex, playing a
create the perception of smell.
smaller role.12.15 Within the central nervous system, informa-
tion from various senses, including taste, smell, and oral soma-
The Interaction of Taste and Olfaction
tosensation, are all integrated to give us the sense and experi-
in her landmark work on the effect of chemotherapy on
ence of flavor.
taste and olfaction, Bartoshuk16 outlined the functional inter-
play of taste and olfaction from which the sensation of “flavor”
Biology of Olfaction
arises. Volatile compounds rise from the mouth into the nasal
the sense of smell originates in the superior region of the
cavity via the olfactory pore, where they interact with olfac-
nasal cavity, where the olfactory epithelium lies. Several im-
tory receptors. unlike taste, which falls into four well-defined
portant cell types compose this pseudostratified columnar epi-
classifications (bitter, salt, sour, and sweet), there is no simi-
thelium. At the base is a thin layer of basal cells that divide
lar classification for olfaction, which is classified on a general
and differentiate throughout life, regenerating the other cell
object-based model (eg, “minty” or “smoky”).
types.12,14 throughout the epithelium are supporting cells that
taste is thought to be an “analytic” sense; that is, its indi-
are believed to play a maintenance role, although their exact
vidual components are each sensed simultaneously. Olfaction,
function remains unclear. Scattered within the olfactory epi-
on the other hand, is generally thought to be a “synthetic” sense:
thelium are specialized glands known as Bowman’s glands that
its individual components blend, creating a holistic sensation dif-
secrete a thin, watery mucus that protects the epithelial surface
ferent from any of the distinct, individual components. Olfac-
while providing a medium for odorant molecules to act. the
tory impairment increases a patient’s perception of disability and
majority of cells in this epithelium, however, are the olfactory
negatively impacts quality of life. in a 14-year study of approxi-
receptor cells, with an average lifespan of 30 days.12
mately 1,400 patients, self-reported “satisfaction with life” was
unlike taste receptor cells, olfactory receptor cells are true
inversely related to degree of subjective (self-graded on a scale
first-order neurons and collectively make up cranial nerve i,
from slight impairment to complete anosmia) olfactory loss.17
providing a direct conduit from the olfactory receptor to the
Another fundamental distinction between taste and smell
central nervous system.14 from each of these bipolar cells, a
is that of “affect,” the pleasurable or unpleasurable associations
dendrite extends apically to the surface of the epithelium, giv-
with a given sensation. taste-related affect appears to be “hard
ing rise to an olfactory knob. long, nonmotile cilia project
wired” and generally fixed, whereas olfactory-related affect ap-
from these knobs into the nasal cavity, creating a large surface
pears to be learned and is labile. the pairing of an odor with a
area for odorant molecules to bind to and interact.12,14
pleasant sensation, such as a high-calorie meal, or, alternative-
Within the membranes of these cilia are the olfactory re-
ly, an unpleasant sensation, such as nausea, influences affect.
ceptor proteins, a diverse family of G-protein–coupled recep-
nevertheless, taste and smell typically act in tandem with
tors encoded by the largest gene family in the human genome.
each other and in concert with other properties to form the
Odorant molecules dissolve within the nasal mucus, then bind
characteristic referred to as palatability. Yeomans18 defines
to one of these G-protein–coupled receptors. Within the cell,
palatability as the hedonic (psychologic) evaluation of oro-
the G-protein G is activated, and it, in turn, activates adeny-
sensory food cues under standardized conditions. the sensory
olf
lyl cyclase iii, which converts AtP to cyclic AMP (cAMP).
properties involved include taste, smell, texture, temperature,
cAMP then binds to cyclic nucleotide-gated ion channels in
visual appearance, sound, and irritative sensations. the litera-
the ciliary membrane, opening them and allowing ca2+ ions
ture examining the relationship between palatability and appe-
volume 7, number 2 ■ march/april 2009
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The Relationship Between Taste, Olfaction, and Nutrition in the Cancer Population
tite is somewhat mixed, but, in general, increased palatability
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