Appetite

Appetite is the body's desire for food. Appetite differs from hunger in that it is a psychological reaction to food rather than a biological one. While hunger induces chemical changes in the body that inform the brain that food is needed to survive, appetite causes people to eat food for enjoyment, even when they are not truly hungry. Hunger, for example, drives people to eat a satisfying meal, while appetite might cause them to continue eating after becoming full simply because the food tastes good.

Hunger is caused by the interaction of the hormones insulin, ghrelin, and leptin in the body. Eating foods high in simple carbohydrates such as sugar raises insulin in the blood, which allows the sugar to enter the body's cells. This makes people crave more food even if they know they are not hungry. The cravings are the result of improperly raised ghrelin, which grows one's appetite. The hormone leptin, meanwhile, would have kept the appetite low after a healthy meal. A number of physical and mental conditions can cause people to experience a decreased appetite or loss of appetite. Loss of appetite can be a symptom of a more serious health condition.

Background

The terms appetite and hunger are frequently used interchangeably, but they are not synonyms. Hunger refers collectively to the biological reactions that arise in people when their bodies require food to continue functioning properly. Hunger activates chemical changes in the body. The amount of the hormone ghrelin begins to rise with the increase in the length of time since a person last ate. When the amount of ghrelin in the body is high, a person will feel extremely hungry. At this point, leptin, a hunger-lowering hormone, is low. As a person eats, ghrelin decreases while leptin increases. This makes people feel full after eating.

Most people feel hunger as an empty feeling in their stomach. The stomach itself may issue an audible rumbling sound known as a hunger pang. These sounds result from normal muscle contractions in the digestive tract. After a person has eaten, the contractions move the food through the tract. If the person has not eaten, the contractions simply squeeze air and make the rumbling sounds.

Appetite, meanwhile, is a person's desire, rather than need, for food. It is more of a psychological or sensory reaction to food than a biological one. Nonetheless, appetite can still activate biological reactions such as salivation and stomach contractions. Appetite is a learned response to food, meaning appetites differ in people based on personal taste in food. People may eat one of a particular food item because they are hungry but then eat several more because they have an appetite for that food. This can be called eating for pleasure.

Overview

Health science has shown that yielding to one's own appetite for certain foods, beyond an amount that will satisfy basic hunger, can be unhealthy. Unhealthy food ingredients such as salt and sugar can interact with chemicals in the body to make the brain want more food. This is generally not true of healthy foods, such as those containing fiber or lean protein, as these tend to keep hunger satisfied over longer periods.

The hunger hormones of insulin, ghrelin, and leptin play important roles in the formation of one's appetite. The pancreas makes the hormone insulin, which is used to help cells absorb glucose, or sugar, from the blood and use it as fuel. Eating foods high in simple carbohydrates—such as those found in white bread, white pasta, candy, and other sugary items—can cause some people's bodies to produce more insulin than needed. This insulin imbalance may make people feel a ravenous desire to continue eating even if they are no longer biologically hungry.

Consuming simple carbohydrates regularly and in high amounts may stimulate people to develop insatiable appetites for those same carbohydrates. These foods taste good, and this leads the person to associate the food with pleasure. Succumbing to a voracious appetite for unhealthy food, however, can led to numerous problems. In addition to possibly gaining weight from eating this way, people may also feel tired all day due to the energy fluctuation occurring in their bodies. Their energy rises and falls irregularly because the body uses simple carbohydrates for energy before it uses calories from healthy food sources, such as protein and fiber. The unhealthy sugar from candy will fuel the body for a short time but will soon be used up, causing the person to feel fatigued and hungry once again. Instead of carbohydrates, people should eat proteins and fiber to suppress their appetite. Protein and fiber lower ghrelin and raise leptin, making people feel full for longer.

Just as an insatiable appetite can eventually lead to health problems, so can a chronically diminished appetite. Loss of appetite is a medical condition known as anorexia. This is distinct from the psychological disorder anorexia nervosa, which refers to a person's compulsive desire to lose weight by not eating. Anorexia is a problem unto itself, since the body is not receiving the nutrients it needs from food. However, a severe loss of appetite can be a symptom of several other medical problems.

For example, appetite loss can result from a viral infection such as influenza, or the flu. The appetite should return once the flu goes away. Serious conditions that can cause loss of appetite include chronic liver disease or kidney disease, heart failure, hepatitis, dementia, or cancer of the colon, stomach, pancreas, or ovaries. A person's appetite may also decrease in response to certain drugs. These include prescription medications such as antibiotics and illegal substances such as amphetamines. Psychological causes of appetite loss include depression, anxiety, and grief.

If anorexia is a symptom of another problem, then a person's appetite should return on its own once the base problem is resolved. People who have decreased appetites due to serious illnesses such as cancer or kidney or liver disease may struggle to want to eat again. Attempting to eat one's favorite foods, eating with family members or friends, and eating in restaurants rather than at home may all help a person with a decreased appetite desire food again.

Individuals who have anorexia but do not know why should consult their doctors. Tests to find the cause of the decreased appetite include a complete blood count; an ultrasound of the abdomen; tests of the liver, thyroid, and kidneys; and X-rays of the esophagus, stomach, and intestines.

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