Miller School Researchers Pursue Answers to the Mysteries of Taste

Why do we eat what we eat? As obvious as it may sound, the strongest determinant, other than availability, is taste. Our reaction to taste — a range of responses from yum to yuck — is often instantaneous yet highly personalized. So we eat what we like, but why do we like what we like? And personal preferences aside, does taste really matter?

For two researchers at the University of Miami Miller School of Medicine, the answer is yes.

“Taste is the unsung hero of the human sensory systems,” said Stephen D. Roper, Ph.D. “We take the sense of taste for granted because it is so stable and reliable. There are relatively few taste-related disorders and diseases, compared with the visual or auditory systems, so we pay less attention to our taste buds than to our eyes or ears. Yet the sense of taste is absolutely essential for living.”

Roper and his colleague Nirupa Chaudhari, Ph.D. — both are professors of physiology and biophysics, and otolaryngology, and faculty members in the Miller School’s Program in Neuroscience — recently co-authored a review article, “Taste buds: cells, signals and synapses,” in the high-impact journal Nature Reviews: Neuroscience that described the advances over the past decade in our understanding of our least-understood sensory system.

The journal’s editor asked them to write the article because their laboratories have often been on the front lines of the field’s research. For instance, restaurants have been touting “umami” flavor — a brothy or meaty taste that is commonly added to some foods in the form of monosodium glutamate — for the past decade. Roper and Chaudhari were the first researchers to document a molecular receptor in taste buds that is responsible for detecting umami taste compounds. The finding was key to bringing umami into the mainstream.

Chaudhari commented on three of the most important findings reviewed in the article:

1. There is specialization among taste bud cells.

“We have known for years that our eyes have different cells that detect either dim light or color and bright light. Steve and I helped establish the parallel for taste buds — that we have different, specialized cells that detect sour vs. sweet taste compounds — and we have done quite a bit of work deciphering how the different cell types do their jobs.”

2. Taste buds are like tiny computers.

“Individual cells detect food chemicals, and the bud then processes this information locally to encode the signals that are sent up to the brain. When they arrive, they are interpreted to produce perceptions such as ‘sweet’ or ‘salty.’”

3. We inherit some of our likes and dislikes.

“Our food preferences have certain genetic origins, particularly the genes for taste receptors in taste buds. Different people have different variants of these genes. If someone has a receptor variant that produces a very strong response to a bitter compound, he or she may avoid foods containing that compound. The trouble is that there are valuable therapeutic, including anti-cancer, compounds in many bitter vegetables. In addition, patients can be non-compliant with medicines that have a bitter after-taste. So learning how to block bitter tastes is a goal that has major health implications.”

Not all of our taste preferences are genetic, however. We begin developing them as infants through experience and observation, starting with breast-feeding.

“Some researchers have shown that what the mother eats is communicated to the infant in part through her milk,” said Roper. “Infants also observe, and later mimic, the mother’s facial expressions when eating certain foods. If she doesn’t like peas, chances are good the child won’t, either. Memory is powerful in other ways, too. Even as an adult, if you eat a certain food and then develop a stomach illness, you may associate a negative experience with that taste and avoid it. Conditioned taste aversion is one of most powerful forms of memory.”

Still, say the authors, as much as our taste preferences and experiences affect our lives, the loss of taste, as happens with some cancer patients, is the most serious taste-related health concern.

“The disappearance of taste after radiation for throat and neck cancers disrupts normal eating, causing a rapid decline in nutrition and health,” said Roper. “Similarly, taste disturbances following certain cancer chemotherapies also seriously degrade the quality of life for the patient by causing a loss of weight just when nutrition is essential for recovery. Taste loss can even make it difficult for patients to swallow. It is not that they lose the ability — they lack the motivation. This is why understanding the regeneration of taste buds from stem cells is now a major goal in our field.”

Many of the remaining areas of investigation involve not the “what” but the “how” of taste.

“A major direction we are currently pursuing is how taste bud cells and nerves talk to each other,” said Chaudhari. “We know that nerves carry information from the taste buds in your mouth to your brain, which is the way you determine what something tastes like. The continuing mystery is that taste bud cells live short lives and die, to be replaced by new cells. The nerves that they connect with, however, last a lifetime. So how do the taste bud cells and nerves find and recognize one another correctly?

“The answers to that question will have implications far beyond just taste. Replacing and regenerating synapses is something that occurs daily throughout the entire nervous system. The nerve synapses that connect with taste buds are readily accessible and identifiable. By studying them, we may learn about fundamental mechanisms that will also begin unlocking the secrets of the brain.”

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