 |
 |
 |
 |
 |
 |
 |
 |
 |
Danielle Renee Reed is a researcher at the Monell Chemical Senses Center who studies the relationship between genetics and complex traits. She was educated at the University of Washington (B.S. in Psychology) and Yale University (Ph.D. in Psychology) and was trained as a postdoctoral fellow in genetics by R. Arlen Price at the University of Pennsylvania. She is currently conducting genetics research funded by the National Institutes of Health and the Pennsylvania Department of Health, and she serves on several government advisory panels. Her interests are in obesity, especially the determinants of body-fat patterning, and individual differences in the ability to taste and smell. In 2008, she received the International Flavor and Fragrance Award for Excellence in Taste Research. Reed commutes to work by bicycle and is the mother of two teenage children, Jesse and John. |
On July 28, 2009, Danielle Reed answered selected viewer questions about taste, its genetic roots, and more. Please note we are no longer accepting questions, but see Tour the Tongue and our Links & Books section for more information. Q: While I have overcome many of my food dislikes from childhood, one in particular escapes my every attempt to subdue it and that is (vegetable) peppers, red, green, yellow, chili, etc. Even the smell of peppers cooking I find distasteful. I can eat and enjoy other foods from this plant family such as potato, tomato, and eggplant with no problems. Could the "supertaster" theory explain this? I also don't care for cilantro (tastes bitter and soapy), which I read once may be an indicator. A: Cilantro contains several volatile (airborne) chemicals that give it a delicious aroma. Unfortunately, due to variations in the genes that code for olfactory (smell) receptors, some people are unable to sense one or more of these compounds. We think that for these people—and you may be one of them—the soapiness of cilantro is not counteracted by the ability to smell its pleasant qualities. The same may be true for peppers; that is, you may not be able to smell the flavor notes that many people find attractive. It is unlikely that being a "supertaster" is responsible for your dislike of peppers because peppers do not typically contain the types of bitter-tasting chemicals most noxious to people having the "supertaster" genetic makeup. Q: I am known by friends as the picky eater. I love to eat, but I am very particular about how the food is combined, the texture, its appearance, and how often I have eaten it. Most of the time I pick what I will eat based on the above, and if nothing seems right I just won't eat. Very bad habit. The first question I have is why does the appearance of food affect my decision on whether I will eat it or not? My second question is how can I eat something I enjoy today, but tomorrow the thought of the same thing grosses me out? This happens all the time, and I know it is very frustrating to my boyfriend (the cook) when planning meals. Thank you for taking the time to answer my questions. I know the people around me will appreciate it as well! A: Your behavior is at the extreme end of a continuum of normal behavior. Eating food that is attractive and carefully prepared is a survival instinct, but most people can overlook less than perfect food when they are hungry. Likewise from a biological standpoint, seeking variety is essential to ensure adequate nutrition since no single food provides every nutrient. You may have a reduced hunger drive relative to your friends, which allows you to seek more variety and focus on food appeal. Q: I know that everyone can taste umami—it's a basic sense. But how about more complex tastes? Vanilla for instance. To me, vanilla ice cream has no flavor—just creamy. I can't taste the difference in foods when it is there or not there; it's always been an optional ingredient. Growing up, vanilla was described as a "leavening ingredient" and never as a flavor. I have other things I am picky about, some weird ones. BUT, I have met several people with the same likes and dislikes as I have. Could there be some genetic component to being picky? My half brother is pickier than I am, yet our parents are all good eaters. A: Flavor is a combination of sensory qualities, and much of what we call "taste" is actually "smell." Accordingly, vanilla is primarily a smell. Classic studies by Blakeslee demonstrated that there is a range of ability to smelling vanilla, and there are indeed some people—and you may be one of them—who are unable to smell its flavorful notes. There is no doubt genetic differences can partially account for a person's pattern of food likes and dislikes, but thus far only a handful of genes and their alleles have been identified that influence some specific responses. It is normal for younger people (you and your half brother) to be pickier than your parents. Food preferences change over time, and so you may come to resemble them more as you approach the age your parents are now. Q: I am a picky eater, and once my dad told me that I won't be picky always because the gene that causes this mutates over time. Is that true? Many of my relatives are picky eaters, and they got over it. A: In general, children are less willing than adults to eat a broad variety of foods, including vegetables, and this age difference in food preferences occurs across many cultures. From an evolutionary perspective, it is adaptive for kids to be more cautious as they learn what is safe to eat. The shift in taste between childhood and adulthood is unlikely to be due to gene mutations (damage to the DNA over time) but may be due to natural changes in the amount of protein produced from a gene. Q: If glutamate types of foods are savory (umami), then why do so many people have an allergy to monosodium glutamate (myself included)? How is this evolutionarily helpful? A: Our love of glutamate evolved to guide us towards nutritious foods like tomatoes and mushrooms, which contain abundant amounts of this amino acid. However, we now add much more concentrated forms like monosodium glutamate (MSG) to our food, and some people like you do not tolerate it. The same logic applies to sugar—it helps guide us to foods like fruits that are healthy, but as we have added more and more concentrated sugars to foods, many people cannot tolerate its effects and become obese and diabetic. Our food habits are changing faster than the ability of our bodies to cope, and this leads to food intolerance and disease in some people. Q: My son is an extremely picky eater, to the point that I feel he almost has anxiety attacks about trying new foods. Is this a genetic condition or more of a psychological condition? He at times seems to have actual "fears" about trying new foods. He also does not like foods with texture to them. Thank you for any guidance you can provide! A: Children are more cautious about food compared to adults and for good reason—they are in the process of learning what is safe to eat. This behavior harkens back to a time when our food supply was more dangerous than it is now, when choosing what to eat was a life-or-death decision (spoiled meat, poisonous plants). Although it is difficult for parents who are trying hard to ensure their children get a broad variety of nutritious foods to remember that pickiness in children was adaptive, it helps to remember that it is normal for children to be cautious (or in your son's case, ultra-cautious) about what they eat. While your son's behavior may seem extreme, many children express trepidation when asked to taste new foods. As children become teenagers and young adults, most eventually eat and enjoy a wide range of foods. Q: Is my ability to taste related to my frequent inability to smell? If so, how? A: A large component of what we casually think about as the "taste" of food is actually due to olfaction (sense of smell). To illustrate this principle, pinch your nose and eat a jelly bean—it is bland until the nose is opened, when there is a rush of flavor. Try the demonstration and you will see how important smell is to the appreciation of food and drink. Q: To keep peace in my marriage, I must eat much of what is unpleasant or intolerable, while my wife thinks everything is "good". How can I reduce my taste sensitivity? A: You are not alone. On average, men and women have different food preferences, and this can translate to discord at the dining room table. Personally, I am sympathetic, because we have the same problem in our house; for instance, I love salads with vinaigrette, but my husband finds them too sour. Keeping in mind that you and your wife have different genetic makeups that may influence how you each perceive the flavor of food, there are two ways to change your food preferences: (1) time and exposure; and (2) manipulating how hungry you are when you eat disliked foods. The more you eat a food, the better you like it. So just showing up at the dinner table every night and eating what is offered will change your preferences. This is your current strategy, but it sounds like you are looking for a quicker fix. The other method is to eat non-preferred foods when very hungry—the body begins to associate those flavors with a positive benefit (relief of hunger). There is a third way to eat the food you like—offer to cook dinner [smile]. Q: From a molecular standpoint, how does the taste bud detect sugar (or the other flavors)? Does the sugar molecule have to fit into a receptor site? Does the sugar form intermolecular bonds with the receptor site that triggers a response? How does this response become an electrical signal down the neuron? Sugars come in different molecular shapes and sizes. Does a taste bud have differently shaped sugar detectors in a single bud? How does it differentiate sugar from a starch? Do you think mice think starches are sweet? A: Sweet receptors are embedded in the taste receptor cells located in taste buds. The process of tasting sweet begins when a sweet chemical interacts with the receptor. There is only one type of sweet receptor, but it is a large and elaborate molecule that has many different sites where chemicals of all shapes and sizes can bind. This contact causes the sweet receptor to change shape and sets off a chain of chemical reactions inside the cell, which eventually results in the cell transmitting an electrical signal to an adjoining taste nerve. This intracellular signaling cascade involves molecules such as G proteins, cAMP, kinases, and an ion channel called TRPM5. It is unlikely that mice or humans detect starch in the same way we detect sugars or other sweet molecules. There are probably unique starch detectors in the mouth, but they have not yet been discovered. Q: Knowing that there is a gene sequence that allows us to sense to a certain degree bitter, are there specific gene sequences that allow us to detect sour or "hot/spicy" more? I love sour tastes (the more sour the better!) but hate bitter or spicy flavors of things. A: There are specific receptors for both sour molecules and spicy molecules, and people do differ in the DNA sequence in the genes that code for these receptors. However, scientists have not yet figured out which alleles are associated with differences in perception. This work is going on right now in laboratories across the world. Q: Dear Dr. Reed, I have what I'm sure is a common question. How do I get my nearly 8-year-old daughter to eat a more healthful diet? She is very picky—will only eat peas and green beans—and is very reticent to try new things. Will this situation improve naturally with time? A: Picky eating is an adaptive strategy for children because they have to learn what is safe. Although this behavior vexes us, bear in mind that this is precisely the cautious behavior that protects children from accidental poisoning. Take comfort in knowing that most children grow out of picky eating over time and that the best strategy to accelerate this process is to offer her wholesome foods and encourage her to taste them as frequently as possible. Speaking as a mother, this is easy to say but hard to do. I was driven to tears at times trying to get my picky children to eat anything other than French fries, but now as teenagers they eat and enjoy exotic and spicy foods as well as Brussels sprouts and spinach. Q: What percent of the population has the active CCD gene to be super receptive to bitter? A: Like the genes for hair or eye color, the frequency of genetic variation that leads to super-sensitivity to certain types of bitter compounds varies by racial ancestry. For instance, about 25 percent of the European population is homozygous for the taster allele (and are super-sensitive to some types of bitter molecules), but this rate approaches 100 percent in Native American populations. For more details, the National Institutes of Health have a useful list of allele frequencies among human populations: Q: Have you conducted any research with regard to so-called "supertasters"? I am interested because I think I am one. I can sometimes taste sharp bitterness in lettuce and other produce that none of my friends seem to notice. They make fun of me, but I take comfort in the fact that I am a supertaster and they are not. A: There are two ways to think about the term "supertaster." In the general sense, some people are more sensitive than others to all types of taste, just like some people have more sensitive hearing or vision than others. If you find all types of food to be more intense than your friends and family, you might be this type of supertaster. The second way people think about supertasters is specific to a type of bitter molecule found in vegetables like turnips or broccoli. Since these particular chemicals are not usually found in lettuce, it is unlikely that you are this type of supertaster. Q: food toxins or poisons and thus help the group survive or avoid group extinction. Do people who avoid bitter foods have different metabolism or nutritional requirements? Do other specific traits such as anxiety or sensitive guts associate with taste sensitivity to bitterness in its many forms? A: This is a useful and interesting scientific question, but we don't yet know if people who avoid bitter differ in metabolism or nutritional requirements from people who are less sensitive to bitter tastes. We know more about the psychology of people who are especially sensitive to certain types of bitter. A recent study suggests they may be more emotional than less bitter-sensitive people. Q: Why do people taste cilantro so differently? For instance, people who like it describe it as a "clean" taste, but to me it tastes like someone dumped shampoo on my food. There are other non-clean tastes described at Ihatecilantro.com. Ever since I moved from Boston to CA, I have to be constantly on the alert because almost every restaurant out here puts cilantro in or on its food, and it ruins it for me. But I've never heard a good explanation for why. Is it a handed molecule, and we have different receptors that it binds to? Or does it mix with different chemicals in our saliva to create a different compound like what sometimes happens with perfume on the skin? A: Cilantro contains compounds that give it a savory smell that drowns out the soapy flavor. However, due to variations in their olfactory receptor genes, some people are unable to smell this pleasing aroma, and thus they only get the unpleasant side of cilantro. In other words, for these people the soapiness of cilantro is not counteracted by the ability to smell its appealing qualities. You might be interested in listening to a recent program about this topic on National Public Radio: Q: Do your genes affect all tastes or just bitter? A: There are separate genes that influence how we respond to each taste. Thus, it is possible that there are people who are sweet-blind or sour-blind, just as some people are bitter-blind. We use bitter blindness as an example of how genes affect taste because we currently understand this best, but genes and alleles have recently been discovered that affect sweet and umami (savory) perception. Stay tuned! Q: My son grew up eating practically nothing but fruits and vegetables and nuts. He did this by choice and disliked cooked food intensely. An adult now, he eats a narrow range of cooked food, but he's still never eaten a hamburger or a hot dog, for example—he says they still smell disgusting. Do you have a genetic or other explanation for a kid who CAN'T stand junk food? A: There is no specific genetic variation associated with the avoidance of cooked foods like meat (that we know of), but it is possible that your son senses (through taste or smell) something most people do not and finds it very off-putting. Having a child that won't eat junk food (even occasionally) would seem like a dream come true to some parents, but it can create social difficulties for both the parent and the child. However, if he is in good health, it would seem prudent to let him follow the wisdom of his own body. Q: Is there any link in your genetic research to explain the "gag" reflex to mushy or stringy food? Has plagued me all my life. Thanks. A: There is no genetic research that would explain your adverse reaction to foods with certain textures. We do know that these types of aversions can develop early in life through experiences, such as eating a stringy food and feeling nauseated because of an unrelated cause (e.g., stomach flu). If you reflect back on your childhood, perhaps drawing on the recollections of your parents or other caretakers, you may be able to pinpoint the formation of this aversion. Q: As an identical twin, how do you explain one twin who hated spinach, broccoli, cauliflower, etc., but his identical twin loved them, when we are genetically the same? My twin brother was anemic. Epigenetics? A: Two points are worth making about your observations. First, identical twins are not actually as genetically identical as once believed. Sometimes the number of genes differs between monozygotic (identical) twins; this is called copy number variation. Other times, the proteins that regulate how much and when genes are turned on and off differ between twins (as you say, epigenetics). So the differences in food likes, physiology, and metabolism between you and your "identical" twin may have a genetic basis. However we should also bear in mind the power of personal experience in learning about food—your brother may have had encounters with vegetables that have led him down a different path. Perhaps anemia led caregivers to push one twin towards certain foods, which set off a vigorous refusal to eat them? |
||||||||||
|
|||||||||||
| |||||||||||
© | Created June 2009 |
|||||||||||
