“It is possible that people with anorexia have difficulty recognizing taste or responding to the pleasure that is associated with food,” said psychiatrist Walter H. Kaye, the director of the Eating Disorders Program at UCSD. The cause of these disorders has long been thought to be social pressure and the desire for control, but if that were the case, there would likely be more cases. Instead, anorexia only afflicts about 0.5 percent of women in the United States, a figure that has stayed consistent for decades. Finding a way to increase the response could be a more effective treatment than traditional counseling and therapy.
Inhibitors for the protein kinase M zeta have been used on laboratory mice to block out memories of foods that the mice did not like, after the inhibitors were injected into the gustatory cortex. Such a treatment may soon be used for anorexic patients in the not-too-distant future. The kinase M zeta protein is also associated with the formation of long-term memories, and beneficial in treatments of dementia as well.
Not only are our taste receptors similar to every living vertebrate — a large catfish has more taste buds on its whiskers than you do on your tongue — but they appear on regions throughout the body that will never come in contact with food — like on the lungs and the heart. Even your brain consists of taste receptors for recognizing sweet and bitter flavors. So far, about 7.9 percent of neurons in the orbitofrontal cortex (just at your forehead) react to taste stimuli. An additional portion of these receptors has been assigned to detect and discriminate particular tastes.
In order to recognize sweetness, saltiness, sourness, and umami, there is only one type of receptor assigned to each of these tastes. Sweet receptors came to be associated with nutrients from fruit and milk, food sources rich in calories. However, there are at least 25 known types of receptors for recognizing bitter tastes. These were perhaps the most crucial throughout our evolutionary history — adaptations that helped us to recognize and avoid ingesting the chemicals from many different types of poisonous plants. In a world without knowledge of microbes, tasting and immediately spitting out stagnant water, or rotten fruit, could have meant the difference between life and death.
We don’t have to worry nearly as much about this in the days of processed food — allowing us to adapt to significantly more nutritious diets than our ancestors ate, and doing this with far more efficiency, spending only a fraction of the time they did on hunting and gathering. Since the days of agriculture, these bitter receptors have had their drawbacks — it’s why most leafy greens (rich in iron and calcium) are a turnoff that we tend to avoid.
These discoveries have led many researchers, such as biologist Noam Cohen, to suspect that these receptors may have served as a primitive line of defense for our immune systems. The evidence certainly fits. Through his research at the University of Pennsylvania, Cohen has come to discover that some people are more susceptible to the respiratory illness rhinosinusitis, based on genetic variations of bitter receptors that occur within certain individuals. By targeting specific variations of these receptors, Cohen hopes to determine why some people are more likely to develop rhinosinusitis — which could mean another significant stride in efforts to create personalized medicine. Instead of antibiotics, researchers like Cohen hope to use bitter compounds that activate taste receptors to attack infections.
Other studies seem to support this linkage. In another experiment, chemosensory cells in a patient’s urinary tract used taste receptors to signal the bladder to release urine, after detecting foreign E. coli bacteria — a measure to prevent infection. Some chronic illnesses such as epilepsy, dreaded even in the days of antiquity, have been known to produce a disagreeable flavor in the mouth when a misfiring in the brain occurs, just before the onset of symptoms. Other bitter receptors such as T2R38 actually work with white blood cells to detect invading bacteria. As modern science moves away from the use of antibiotics (notoriously bad for the immune system and at fighting strains of “superbacteria”), perhaps we’ll find that the solution has been among us all along — so close we could almost taste it.
This article was first published in the print edition of Brain World Magazine.
