People Can Taste Flavor With Smell Receptors, Not Just Taste Ones

According to the latest research, the flavor of food is also a result of cell receptors associated with smelling things.

Scientists from the Monell Center report that functional olfactory receptors, the sensors that detect odors in the nose, are also present in human taste cells found on the tongue. The findings suggest that interactions between the senses of smell and taste, the primary components of food flavor, may begin on the tongue and not in the brain, as previously thought.

“Our research may help explain how odor molecules modulate taste perception,” said study senior author Mehmet Hakan Ozdener, MD, PhD, MPH, a cell biologist at Monell. “This may lead to the development of odor-based taste modifiers that can help combat the excess salt, sugar, and fat intake associated with diet-related diseases such as obesity and diabetes.”

While many people equate flavor with taste, the distinctive flavor of most foods and drinks comes more from smell than it does from taste. Taste, which detects sweet, salty, sour, bitter, and umami (savory) molecules on the tongue, evolved as a gatekeeper to evaluate the nutrient value and potential toxicity of what we put in our mouths. Smell provides detailed information about the quality of food flavor, for example, is that banana, licorice, or cherry? The brain combines input from taste, smell, and other senses to create the multi-modal sensation of flavor.

Until now, taste and smell were considered to be independent sensory systems that did not interact until their respective information reached the brain. Ozdener was prompted to challenge this belief when his 12-year-old son asked him if snakes extend their tongues so they can smell.

In the study, published online ahead of print in Chemical Senses, Ozdener and colleagues used methods developed at Monell to maintain living human taste cells in culture. Using genetic and biochemical methods to probe the taste cell cultures, the researchers found that the human taste cells contain many key molecules known to be present in olfactory receptors.

They next used a method known as calcium imaging to show that the cultured taste cells respond to odor molecules in a manner similar to olfactory receptor cells.

Together, the findings provide the first demonstration of functional olfactory receptors in human taste cells, suggesting that olfactory receptors may play a role in the taste system by interacting with taste receptor cells on the tongue. Supporting this possibility, other experiments by the Monell scientists demonstrated that a single taste cell can contain both taste and olfactory receptors.

“The presence of olfactory receptors and taste receptors in the same cell will provide us with exciting opportunities to study interactions between odor and taste stimuli on the tongue,” said Ozdener.

In addition to providing insight into the nature and mechanisms of smell and taste interactions, the findings also may provide a tool to increase understanding of how the olfactory system detects odors. Scientists still do not know what molecules activate the vast majority of the 400 different types of functional human olfactory receptors.

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Obesity May Dull the Sense of Taste

The study here found that obese mice had about 25 percent fewer taste buds than mice of a healthy weight. As some similar effect is likely found in humans, this research should provide an increased motivation (that is, enjoyment of food) for reducing the obesity epidemic, which I have written about at more length before.

Previous studies have indicated that weight gain can reduce one’s sensitivity to the taste of food, and that this effect can be reversed when the weight is lost again, but it’s been unclear as to how this phenomenon arises. Now a study publishing March 20 in the open-access journal PLOS Biology by Andrew Kaufman, Robin Dando, and colleagues at Cornell University shows that inflammation, driven by obesity, actually reduces the number of taste buds on the tongues of mice.

A taste bud comprises of approximately 50 to 100 cells of three major types, each with different roles in sensing the five primary tastes (salt, sweet, bitter, sour, and umami). Taste bud cells turn over quickly, with an average lifespan of just 10 days. To explore changes in taste buds in obesity, the authors fed mice either a normal diet made up of 14% fat, or an obesogenic diet containing 58% fat. Perhaps unsurprisingly, after 8 weeks, the mice fed the obesogenic diet weigh about one-third more than those receiving normal chow. But strikingly, the obese mice had about 25% fewer taste buds than the lean mice, with no change in the average size or the distribution of the three cell types within individual buds.