Aug. 13, 2010

What is responsible for our taste preferences and why do they change with age?

by Molly Nickerson

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Our tongue senses only five different tastes- sweet, sour, bitter, salty, and a fifth called umami. The umami responds to salts of glutamic acid, which would be associated with meat broth or aged cheese. Taste receptors function through either a transmembrane ion channel (sour and salty) or a G-protein-coupled receptor (sweet and bitter) and are bundled in groups of 50-150 to form taste buds. Each taste bud probably has a few representatives from each of the five taste classes, but receptors for each of these tastes are focused in different sections of the tongue (see diagram). Each receptor sends a message to the brain, which is the ultimate taste center. The proportion to which various receptors are stimulated is summed within our brains to create a certain taste.

Taste preferences and aversions are related to both physiology and psychology. In a physiological sense, we will crave foods that fulfill our body’s needs. For example, we will crave salt when our electrolyte balance is off and crave sweets when we feel like we need calories. The placement of the sweet receptors on the tip of the tongue is probably no accident- our brains need sugar to keep running and so we seek it out first and foremost. If you want to know how something tastes, you stick the tip of your tongue on it. A sweet sensation will likely elicit a response from your brain that the tasted object would be good to eat. Taste aversions are often associated with foods that have made us ill. Taste aversions can be stronger than our innate senses. For example, a rodent can be made to hate sweet treats if we associate them with something that makes the rodent sick.

Bitter flavors typically signify natural toxins and sour flavors signify the presence of acid. We often include these flavors in our food choices, which may in part be due to the fact that we have trained our palates to be more sophisticated than those of our evolutionary forbearers. Sour and bitter flavors can be used to balance sweet and salty flavors, bringing balance and variety to our meals. The ability to sense bitter tastes, however, is a dominant genetic trait that follows a classical Mendelian pattern; about a quarter of people hardly taste bitter at all, half of people taste bitter to a moderate degree, and about a quarter of people are very sensitive to bitter flavors. This is one way in which individuals differ in their taste preferences. This genetic component of individual taste preferences is strengthened by our sense of smell, which is based on the smell receptors that we inherit and, in turn, have a huge impact on how we taste things. In fact, up to 75% of what we perceive as taste may actually be smell!

The psychological side of taste is quite interesting, as well. I think that we all have comfort food, nostalgic food, a social drink, or childhood treat. These dishes- fried chicken, chocolate chip cookies, gin and tonic, ice cream, whatever- are attractive to us for more reasons than our physiological needs. Smelling and eating these foods tap into our memory banks and gets the attention of our reward centers. We each have our own experiences and environments that direct these unique food preferences.

As we age, both the physiological and psychological sides of taste change. Not only do we have more foods to be nostalgic or emotional about, but we lose taste buds from the top of our mouth and side of our tongue so that all of our taste sensation is focused on the center of the tongue (salty and sweet). As we age further, this section of the tongue also gets less sensitive and food seems blander. One response may be to add more sugar and salt to food. As we age, we may seek a bit more “kick” in our food through spices such as chili peppers, wasabi, or ginger. Although these elements seem to add more flavor to our food, they actually work through a system that is completely separate from our taste buds. Our sense of taste can be further reduced during life from smoking, scalding, allergies, medications that are commonly taken by older people, tooth decay, or head injury. As one’s sense of smell decreases around the age of 60, taste perception also decreases.

Unlike fish, who can taste with their fins, we humans are limited to our little tongue and nose. So, enjoy your food while you can and be responsible about how you eat in your later years. If you are bored with food, try adding a little spice.

About Molly Nickerson

The views expressed are those of the author and are not necessarily those of Science Friday.

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