The traditional map of flavors in the language that was learned in school is a myth. That semicircle at the tip that delimited the perception of sweetness or those points on both sides that appreciated saltiness are, in reality, an erroneous or simplistic interpretation of how that entire intricate sensory network that makes up taste really works. Try it: if you place a few grains of salt on the tip of your tongue – the traditional jurisdiction of the sweet taste – you will perfectly detect that salty sensation. Science has shown that the sense of taste is much more complex than the schematic drawing in textbooks and also goes beyond the mouth.
A scientific review published in the journal New England Journal of Medicine He has reviewed how exactly the perception of flavors works in the mouth and has remembered that other organs, such as the intestine, also have taste receptors. “It’s time to let go of old ideas, like the myth of the tongue’s taste map (which persists in the collective consciousness despite decades of research debunking it) and the notion that taste is limited to the mouth. “Research reveals that downstream signaling from extraoral taste receptors regulates our physiological balance long after conscious taste has faded,” endocrinologist Josephine M. Egan of the National Institute of Medicine’s Clinical Research Laboratory proclaims in the article. Aging America.
The journey of the sense of taste begins when chemicals, food flavorings, reach the mouth and activate taste receptors. These cells, which are buried in the taste buds, are the ones that recognize the primary sensory qualities, the five flavors: sweet, salty, bitter, sour and umami. Human beings can have up to 4,500 taste buds and each of them has about 60 taste receptors. Once activated, these sensory cells send flavor information to the brain and it integrates it, in turn, with the stimuli that come from the sense of smell and the information conveyed by the trigeminal nerve (in charge of registering texture, temperature or pain, for example) to build that complex perception of taste, explains Egan.
In this context, he adds, the taste map that appeared in textbooks, with the primary taste qualities concentrated in specific areas, “is not accurate.” “Taste receptors sensitive to each flavoring are present in the taste buds of the entire tongue, which means that there is no taste map that represents regions of the tongue corresponding to specific tastes,” she clarifies.
José Manuel Morales, member of the Otology commission of the Spanish Society of Otorhinolaryngology and Head and Neck Surgery (SEORL-CCC), points out that, indeed, the scheme with flavors by color on the tongue is “quite simplistic.” “That comes from a misinterpretation of a German article from the early 20th century. Yes, there are different sensitivity thresholds in different areas of the tongue, but that was interpreted as privative areas. And it is not like that. There are taste buds on the tongue and they all perceive everything. But, depending on these stimulation thresholds, some flavors or others are perceived more,” he points out.
The “evolutionary guardian”
The perception of a flavor is subjective, but taste qualities have meaning for the body. Taste is, in Egan’s words, a kind of “evolutionary guardian” of the substances that enter the body because it guides human beings towards tasty foods that contain energy and away from dangerous substances. Thus, he says, the preference for sweetness is “innate, it develops long before birth and the consumption of sweet flavors generates satisfaction through central reward pathways.” Bitter and acidic flavors, on the other hand, detect potentially toxic substances and hence the innate aversion to these flavors, although it is a rejection that can be overcome with “acquired preference and masking with sweet flavors,” the scientist clarifies.
Dietary patterns, in any case, also shape taste, agrees Egan: “Western diets rich in fats and carbohydrates change the proteomic landscape of the tongue and obese and diabetic mice and their offspring have a greater preference for sweet stimuli.” . The researcher adds, however, that a direct connection between obesity and taste perception in humans has not yet been demonstrated.
However, the sense of taste does not end in the mouth either. There are extraoral receptors that, although they do not directly perceive flavors as on the tongue, are also activated in one way or another when different taste stimuli reach them. “Researchers have discovered diverse functions of extraoral taste receptors, such as regulating male fertility and protecting tissue in the pulmonary vasculature. The intestine has emerged as a site to explore the participation of taste receptors and their subsequent signaling pathways in appetite, nutrition and diseases,” the scientist summarizes in the article.
Taste is not an isolated sense in the mouth. Morales points out, in fact, that “the most important thing for the interpretation of flavors” is the “interrelation between smell and taste.” “In order for you to perceive the nuances of a flavor, you need your sense of smell,” he defends.
Beyond the mouth
Regarding the taste receptors beyond the mouth, he makes a point: “It is not that we have taste buds in other parts of the body. But there are receptors in the cells that are similar to those in the cells of the salivary glands and that can be activated with the same elements. And these can influence the secretion of dopamine, the feeling of greater or lesser satiety or the secretion of insulin.”
But this does not mean that the intestine, for example, can perceive a specific flavor: “The functioning of the receptors in the intestine does not transmit the sensation of taste, but rather triggers a process of regulation or deregulation of insulin or something else.” And he gives an example to understand it: “A patient with stomach cancer, who undergoes a gastrostomy [colocación de una sonda de alimentación que va directamente al estómago], does not eat by mouth. If we were able to perceive flavor in the intestine, that patient could tell if what was coming to him or her was sweet or salty. And he can’t. Because flavor, as we all understand it, is detected in the mouth. “Receptors in other parts of the body have another function.”
Diego Bohórquez, a neuroscientist at Duke University, discovered in animal studies that cells that detect glucose in the intestine not only identify it, but also distinguish it from other sweeteners and communicate that information to the brain using different neurotransmitters. “When the mouse is stimulated, it chooses to consume the glucose because that brings it calories and the sweetener does not. And when we turn off these cells in the intestine—not on the tongue—the mouse literally becomes blind and cannot distinguish between a sweetener and a sugar,” he says.
There are taste buds on the tongue and they all perceive everything. But, depending on these stimulation thresholds, some flavors or others are perceived more.”
José Manuel Morales, doctor of the Spanish Society of Otorhinolaryngology
Extrapolated to humans, the researcher gives as an example the global preference for sugary soft drinks compared to their low-calorie counterparts. “We instinctively prefer sugar more than sweetener. And the fascinating thing is that before it was believed that it was only in the language and, in reality, it is the intestine that is guiding that decision making,” he defends.
In this context, he says, language “simply creates an initial, alert representation.” If it is something toxic, the tongue will say no and will not consume it. But once the mouth accepts food, you have to “trust” the intestine, he says: “The intestine has to detect, discern, communicate and react to that stimulus. And we are realizing that the intestine not only changes with respect to the stimulus, but on many occasions, it also anticipates the stimulus. “The change in the sensory ability of the gut is what causes us to crave a certain food.”
Thus, stimulating the taste receptors on the tongue is not the same as not receiving the stimulation of sugar in the intestine, exemplifies Bohórquez: “There are some references that chewing gum causes reflux in many people and causes reflux because it is receiving the candy here [en la boca] and the intestine is preparing, but it does not receive the sugar. Then he gets irritated and petulant.”
More flavors
The confines of taste are still being investigated, how far the role of each organ goes and how that representation of meaning is constructed. There is even talk of new flavors, such as fat. Although there is debate there. “This is like a color palette, that with the three basic basics you can obtain the entire chromatic range,” Morales exemplifies. “Flavors are obtained with a combination of the different flavor qualities of food. Fatty or metallic flavor are combinations of the five basic ones. Is spiciness a flavor? Not for me. Gustatory sensitivity is a combination of sensations chemicals but also perception through the trigeminal, which gives us the sensation of temperature and texture. If spicy produces a trigeminal sensation, I would not identify it as a flavor,” he explains.
Bohórquez also highlights the subjectivity of perception: “The beauty of biology is that diversity, which with a combination of five things and the variability that can exist in each of the receptors, creates such a diverse representation of the world for each individual, which is completely unique. What is sweet for you is completely different than what is sweet for me, even though we are talking about a chemical that is completely standardized.”
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