Aversion to Food
AVERSION TO FOOD
AVERSION TO FOOD. Food aversions are far more common, far more diverse both within and across cultures, and far stronger than is often realized. Examination of the characteristics and origins of food aversions can help to illustrate the many contributions of genes and environment to behavior. Further, an understanding of food aversions can be useful in understanding, as well as treating, many eating and drinking disorders.
Classification of Food Aversions
Food aversions have been classified into four types: foods that are rejected because they are dangerous, inappropriate, disgusting, or distasteful. We consider foods to be dangerous, and therefore do not eat these foods, if eating them has previously resulted in physical harm, or if eating these foods is reputed to cause physical harm. However, a dangerous food, such as poisonous mushrooms, would be eaten by someone if there were some medication to prevent any illness from occurring.
Inappropriate foods are items that we consider not to be food. An example of an inappropriate food would be Kentucky bluegrass. Although deer and other herbivores might eat this grass, we would consider it inappropriate for humans to do so. Similarly, there may be an item, such as a particular kind of berry, that is considered to be a food by one culture but not by another.
There are several reasons why someone might treat an item as an inappropriate food. One involves the taste of the item. From birth, humans find certain tastes, notably the taste of bitter, to be aversive, and therefore may not consider items with those tastes to be appropriate foods. For example, many wild plants taste extremely bitter. Given that poisonous plants are often bitter, scientists believe that humans who avoided bitter tastes were more likely to survive and therefore humans evolved to have an innate aversion to bitter tastes. Direct experience with an item may also contribute to its classification as an inappropriate food; attempts to chew some wild plants can be fruitless. Finally, someone may consider an item to be an inappropriate food because of information passed on by someone else. For example, caregivers may tell children that grass is not food.
Disgusting foods are those that most of us would not want in our meals or stomachs no matter how the foods were disguised and no matter how small the amount. Some examples of items classified as disgusting foods are urine and feces. Foods can become disgusting because of someone's having observed others' reactions to these foods, because of contact of a previously nondisgusting food with something considered disgusting, or because a food looks similar to something disgusting. Thus, because most American children learn from others that insects are disgusting foods, we consider a glass of milk that used to have a cockroach in it to be disgusting, and we find fudge that looks similar to feces to be disgusting. Similarly, cultural beliefs can result in certain foods being considered disgusting. For example, many vegetarians consider meat to be disgusting, and Jews who keep kosher may find meal combinations of meat and dairy products to be disgusting.
Probably the most studied is the fourth and final category: distasteful foods. These are foods that most of us would not mind eating if the taste of the food were covered up by another taste, or if we only found out that we had eaten it after we had finished eating. An example is warm milk. Once again, an innate dislike of certain tastes can contribute to food aversions of this sort. However, many members of the distasteful food category are illness-induced food aversions (also known as taste aversions). Humans and many other species exhibit illnessinduced food aversions when they eat something, become ill, and then do not want to eat that food again. This is an extremely powerful type of learning. Study of the acquisition of illness-induced food aversions has proved extremely important to the development of general learning theory, and has resulted in a number of different applications outside of the laboratory. Therefore, the following sections discuss illness-induced food aversion learning in some detail.
Taste Aversion Learning: Basic Observations
Prior to scientists' conducting any investigations of taste aversion learning, farmers were aware of this phenomenon, which they called bait shyness. The farmers found that it was difficult to kill rats by putting out poisoned bait. The rats would take only small samples of any new food, in this case the bait, and if they then became ill, they would subsequently avoid the bait.
Laboratory experiments on taste aversion learning began in the 1950s. Researchers noticed that rats eat less after being irradiated. Apparently irradiation makes rats gastrointestinally ill and they associate the illness with food, resulting in a taste aversion to the food.
In 1966 John Garcia and Robert A. Koelling used a taste aversion paradigm to show learning theorists that it is easier to learn some associations than others. In their experiment, rats more easily learned to avoid licking flavored water when that licking was followed by illness than by shock, and they more easily learned to avoid licking water accompanied by clicks and light flashes when that licking was followed by shock than by illness. Garcia and Koelling concluded that it is easier for rats to associate tastes with illness and audiovisual events with shock than vice versa. It was due to results such as these that this type of learning was labeled taste aversion learning.
Odors may also play an important role in food aversions linked to illness, yet the term "taste aversion learning" has persisted. The fact that tastes and odors are more easily associated with illness than with other sorts of events helps us to survive. The presence of a poison is more likely to be indicated by a particular odor or taste than by a particular appearance or sound.
Subsequent experiments found that taste aversion learning has some other special properties that may help animals to survive. For example, taste aversions can be acquired with up to twenty-four hours between consumption of the food and illness. This is advantageous because it may take hours before a poison will result in illness. In addition, in taste aversion learning, the taste actually seems to come to taste bad. This also helps animals to survive because a poison should be avoided no matter under what circumstances it is encountered. Finally, taste aversions are more likely to form to novel foods, and often form after just one pairing of a taste with illness. These characteristics help to ensure that, as much as possible, animals learn quickly to avoid new poisonous foods. Animals appear to have evolved so that they easily acquire long-lasting aversions to cues associated with poisonous foods.
Taste aversion learning has been studied in a great many species, including humans. Surveys have found that most college students report having acquired at least one taste aversion. In general these aversions are strong and have persisted a long time. Laboratory experiments have shown that taste aversions are acquired similarly across species.
Applications of Taste Aversion Learning
Research on taste aversion learning can help us to understand, and possibly modify, many food aversions and preferences. For example, taste aversion learning may cause what are termed specific hungers. These are preferences for specific foods containing a nutrient, such as thiamine or sodium, in which an animal's diet has been deficient. Animals may feel ill when deficient in these nutrients, and thus form taste aversions to their usual foods. New foods, or foods associated with recovery from the illness, are therefore preferred.
In a very different application, taste aversion learning has been used for wildlife management—to prevent coyotes from attacking sheep on ranches in the western part of the United States. Many ranchers choose simply to kill the coyotes. However, coyotes are a valuable part of the ecosystem (for example, by decreasing the rabbit population). Researchers reasoned that, if they could train the coyotes to avoid sheep but not rabbits, this would preserve the ecosystem. They therefore placed lamb bait laced with an illness-inducing drug on the range in areas frequented by coyotes. The coyotes appeared to acquire an aversion to eating or even approaching sheep. In fact, after aversion training, coyotes behave submissively toward sheep, running the other way when a sheep approaches.
Taste aversion learning has also been helpful in understanding the life-threatening anorexia that can accompany cancer. Some cancer treatments, such as radiation and chemotherapy, can cause gastrointestinal illness. When this illness is paired with food consumption, taste aversions can result. Ilene L. Bernstein and Mary M. Webster gave child and adult patients a novel-tasting ice cream prior to their chemotherapy and the patients acquired an aversion to that ice cream. These findings and others have resulted in the development of the "scapegoat technique." This technique involves giving cancer patients a novel food along with some familiar food just prior to their chemotherapy. The patient forms an aversion to the novel food and not to the familiar, usual food.
Although it might seem that taste aversion learning could be useful in decreasing overeating, it is not employed for this purpose. Taste aversions form to specific foods, and it is too easy for a patient to switch to overeating a different food once an aversion has been acquired to a previously overconsumed food.
In contrast, taste aversion learning has been successfully employed in treating alcohol abuse, although the pairing of alcohol and illness must be done carefully in order for strong taste aversions to develop. In addition, it is necessary for illness to be paired with a variety of alcoholic beverages in order to ensure that an alcoholic does not switch to new alcoholic beverages following aversion training.
There are a great many different types of food aversions in humans and other animals. Some of these aversions help animals to survive, and others can be extremely debilitating. Continuing research will help to maximize the positive effects of these aversions, and minimize their negative effects.
See also Additives ; Anorexia, Bulimia ; Bioactive Food Components ; Disgust ; Food Safety ; Sensation and the Senses ; Taboos ; Toxins, Unnatural, and Food Safety .
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Alexander W. Logue
Martin E. P. Seligman (president of the American Psychological Association in 1998) has described how, in 1972, he ate sauce béarnaise on steak and then became ill with what was definitely stomach flu (his colleague at work who had not eaten the steak came down with the same affliction, and his wife who had eaten the steak did not). Yet, even though he was absolutely convinced that the sauce béarnaise did not cause his illness, Seligman acquired an aversion to it. *
Some children and pregnant women repeatedly consume nonnutritive substances such as paint, plaster, and dirt. Because such food cravings are most likely to appear in people who need a lot of nutrients, it has been proposed that these cravings are the result of specific hungers for minerals such as iron.