Many people have an aversion to a particular food or drink. In many cases this is the result of an incident in which they became ill after eating or drinking it. Many animal species, and also humans, have an innate mechanism that ensures that they learn to avoid toxic or dangerous substances. This mechanism is called aversion learning. If rats become ill after eating something unfamiliar to them, they will never eat that food again. This was discovered by the Spanish psychologist John Garcia and his colleagues. The rats also learn this aversion to a certain new food if they are artificially made ill, for example by injecting a nauseous substance.
This so-called aversion learning also occurs in humans. An example of this is someone who drank milk that was no longer good, got food poisoning, and then never wanted to drink milk again. Or someone who threw up terribly after drinking whiskey, and from that moment on no longer likes whiskey.
But even if, for example, someone gets a stomach flu after eating a new type of food, an aversion to this food can occur. This aversion often persists for life, despite the person being aware that the illness had nothing to do with the food eaten.
Conditions for the occurrence of aversion learning
The phenomenon only occurs if:
- Becoming ill occurs between twenty-four and twenty-four hours
- It concerns a food or drink that has rarely or never been eaten or drunk before
Aversion learning is explained by many psychologists by the mechanism of classical conditioning . In short, classical conditioning boils down to two events that occur one after the other and thus become associated with each other. An example of this is rattling a box of dog food and then receiving food. (for a more detailed explanation of classical conditioning, see: classical conditioning). But according to Garcia, the leading researcher of aversion learning, this explanation is inadequate. He mentions two crucial differences with classical conditioning.
Difference with classical conditioning
In classical conditioning, the two events (such as rattling the dog biscuits and actually feeding them) must occur within a few seconds, otherwise no association will occur. Aversion learning, on the other hand, only occurs when the organism becomes ill within a period of a few minutes to twenty-four hours after eating or drinking.
A second difference is that in classical conditioning almost all stimuli (events) are suitable for associating with a second stimulus (a sound, an odor, a visual stimulus, and so on). Aversion learning for food or drink, however, only works with an odor or taste.
A mechanism that protects us from poison and spoiled food
The fact that aversion learning cannot be explained as simple classical conditioning suggests that it is a mechanism in its own right. It is likely that it arose during evolution to protect organisms from poison and spoiled food.
Poison and spoiled food do not make someone sick within seconds. This generally takes several minutes to hours, because the substance has only then been absorbed by the digestive system. This is consistent with the conditions for learning food aversion.
A second indication is that only the smell or taste of food can cause a learned aversion. This also makes sense if it is a mechanism that protects us from spoiled food. After all, a spoiled food often looks the same as a healthy one.
Unlearn aversion
The only way to get rid of a food aversion is to eat the food in question often despite the aversion. As the body finds that it can eat the food over and over again without getting sick, the aversion slowly but surely decreases until it is eventually no longer present.