The Whole Package: The Relationship between Taste and Smell

     A couple of days ago I was watching one of my favorite shows, Top Chef, a reality TV show in which contestants try to “outcook” each other in multiple competitions to become the ultimate “Top Chef”.  During one of the final episodes a contestant, who was being asked as to why his food tasted so bland, admitted to the judging panel that he had a weak sense of smell, which caused the judges to almost recoil in disgust.  They told the contestant that, to be a “Top Chef”, one must have the perfect sense of smell, or at least a very strong one, because smell is one of the most important factors in understanding the tastes of food.  While I had heard that smell does indeed have an important part in taste, I was not exactly sure why this was true.  It surprised me to read, when I began my research, that about 90% of what we believe to be taste is really due to smell.  I decided to use this paper as a way to further understand the “mechanics” of taste and smell, the relationship between taste and smell, and what effect smell and taste disorders can have in our lives.

      Smell, one of the five senses, is considered a “direct” sense (1).  When something has a smell, it releases volatile molecules that float through the air to your nose (these molecules are able easily evaporate in the air and are therefore able to move easily and quickly).  Within your nose there are cilia, which are little hairs that increase the surface area of your nose so as to increase your smell perception.  The molecules released from the object being smelled bind to the cilia, or chemoreceptors, where one of many neurons are triggered so that the sense of smell is perceived (2).  Each of these neurons is called an olfactory receptor, and the thousands of them (an average of 10,000) contained in your nose each perceive a different odor (1).  When a chemoreceptor is triggered, an electrical impulse is passed to the brain, where specific odors will then be classified into specific odors inside the brain (2).  Each receptor is encoded by a specific gene, so if a person is missing that certain gene they will not have the receptor to bind to that certain odor, and therefore won’t be able to smell certain items.  For example, if a person were missing the gene that coded for the receptor that sensed esters (organic molecules released from flowers), they would not be able to perceive the smell of flowers.  Another interesting factor about smell is that is it is specifically linked to parts of the brain that deal with emotion.  The olfactory bulb (the part of the brain that changes sensation into perception) is part of the limbic system, and the nose is closely related to this system and therefore triggers behavior, memory and mood (2). 

      Taste is another one of the five senses.  Humans have five primary tastes: salty, sweet, sour, bitter and umami (this is a response to glutimac acids, or MSG).   When someone eats food, the “dissolved molecules and ions” of that food are called tastants (3).  The tongue has taste buds, each of which contains 50-100 taste cells.  Each of these cells is able to determine all five of the primary taste sensations.  On the surface of each taste cell are receptors (transmembrane proteins).  The receptors will either admit ions (for sweet and salty taste) into the cell, or the receptors will bind to molecules (these molecules are the sensations for bitter, salty or umami) (3).  Every taste receptor is connected to a sensory neuron (like the chemoreceptors in the nose) that responds back to the brain when it is stimulated with a molecule; however the actual sensation of taste resides in the brain (3).  Just like the path of smell sensations, the path of response to taste receptions is similar and can possibly explain why taste and smell are so closely related. 

      So, why are taste receptions and smell receptions so closely related?  Why is it that, if we are sick, we can hardly taste what we are eating because our nose is blocked?  Why would it be detrimental for a chef to not have that good of a sense of smell?  Actually, the relationship is like this because “what we often call taste is in fact flavor. Flavor is a combination of taste, smell, texture (touch sensation) and other physical features (e.g. temperature)” (4).  When we eat, the reception that our taste buds get also react to the odors released by the food and therefore we are able to identify what it is we are actually eating (5).  If we didn’t have a sense of smell, then we could distinguish between something that might be sweet and something that is bitter, but we wouldn’t know which food was which because we identify the food based on smell.  This would explain the detriment bestowed upon a chef if he or she were only able to taste, but not smell.  They would not be able to understand the full complexities of the ingredients they were working with and, because cooking is such a chemical process, they would never be able to find a “perfect combination” of ingredients for a meal.  They wouldn’t be able to understand what factors may turn some people on and off to certain foods.  In a way, tasting is only half the package for enjoying food.

      This leads me to wonder if taste or smell disorders are common, and whether they have a major effect on someone’s life.  In smell disorders, hyposmia involves the ability of smell being reduced, whereas anosmia is having no smell at all (6).  Hypogeusia is one of the most common taste disorders, which involves a decreased sense of taste in all primary taste sensations (salty, sour, sweet, bitter and umami).  Another type of taste disorder, ageusia, involves the person having no taste reception as all.  However, “True taste loss is rare; perceived loss usually reflects a smell loss, which is often confused with a taste loss” (5).  This shows how closely taste and smell are related to one another: even the disorders are affected by one another.  The disorders for each sense are somewhat related-either having decreased reception or no reception of taste at all.  These disorders also play an important part in the person’s life.  Smell is important in our lives because it allows us to sense danger (such as smoke from a fire or a gas leak).  Smell also is involved with other diseases: a person with a weaken sense of smell is more susceptible to certain diseases.  “Obesity, diabetes, hypertension, malnutrition, Parkinson's disease, Alzheimer's disease, multiple sclerosis, and Korsakoff's psychosis are all accompanied or signaled by chemosensory problems like smell disorders” (6).   As for taste disorders, taste are also important in someone’s life for the perception of danger (such as poisons, foods we are allergic to, spoiled food).  A person can even become depressed because they are unable to enjoy food.  And, just as with smell disorders, taste disorders can lead to such diseases as “obesity, diabetes, hypertension, malnutrition, and some degenerative diseases of the nervous system such as Parkinson's disease, Alzheimer's disease, and Korsakoff's psychosis” because of the abnormal functions of the chemosensory functions (5).  The  close relationship between smell and taste can also be seen by the diseases that can be caused if a person has a weakened sense of either taste or smell. 

      Not only is the relationship between tastes and smell important for enjoying food, drink and other things, but the disruption of the relationship can lead to many more problems, such as the diseases listed above.  The relationship between taste and sense is one of the most important in the human body system and can have a major impact on a person’s life.  Not only would a decreased sense of smell be a huge detriment for a professional chef, but it would also affect someone who would just be enjoying food for pleasure.  Smells and taste are also natural defenses that protect humans from danger (poison, fire, etc).  As experiments are further conducted to understand the relationship between smell and taste, hopefully treatments will be found to help heighten not only just smell or taste reception, but both together.  Whereas some treatments have been discovered (and some taste and smell disorders can be recovered spontaneously) it would be important to try to find a surefire treatment.  Then, everyone (not just chefs) could enjoy food and the pleasure that it gives us.

Primary Sources:

1)       http://health.howstuffworks.com/question139.htm. 1998-2007, HowStuffWorks, Inc.

2)       http://health.howstuffworks.com/smell.htm 1998-2007, HowStuffWorks, Inc.

3)       http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Taste.html 25 February, 2007

4)       http://www.cf.ac.uk/biosi/staff/jacob/teaching/sensory/taste.html Tim Jacob, 26 March 2007

5)       http://www.nidcd.nih.gov/health/smelltaste/taste.asp National Institute on Deafness and Other Communication Disorders, March 2002

6)       http://www.nidcd.nih.gov/health/smelltaste/smell.asp#what National Institute on Deafness and Other Communication Disorders, March 2002