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Appetite

life science Maturity 11-13 Next article →

Appetite is the biological desire to consume food. It exists in all higher life-forms to regulate energy intake. This process ensures that an organism meets its specific metabolic needs. While we usually associate appetite with hunger, it is actually a distinct feeling. Appealing foods can stimulate appetite even when a person is not hungry.

Piece of chocolate cake on a white plate decorated with chocolate sauce
Piece of chocolate cake on a white plate decorated with chocolate sauce

Conversely, the feeling of satiety, or being full, can greatly reduce appetite.

Appetite is managed by a complex interplay between the brain, the digestive tract, and adipose tissue. Adipose tissue is the body fat used for energy storage. Two primary hormones drive this communication through the bloodstream. Ghrelin is an orexigenic hormone released from the stomach. It stimulates feelings of hunger in the brain. Leptin is a hormone released from adipose cells. It stimulates feelings of satisfaction after eating. The balance of these two signals is vital for maintaining healthy energy levels.

Sometimes, this hormonal balance becomes disrupted. In cases of obesity, a person may develop resistance to leptin. This occurs when body fat accumulates and causes an overproduction of leptin. The hypothalamus, a part of the brain, stops responding to the hormone. Once this happens, ghrelin production can cause an insatiable appetite. Other physiological issues can affect appetite without involving genes. For example, dyspepsia, or indigestion, can make a person feel overly full very quickly. Changes in taste or smell, known as dysgeusia, can also lower the desire to eat.

Genetic factors play a significant role in how appetite is regulated. In the 1950s, researchers discovered Prader–Willi syndrome. This is a type of obesity caused by specific chromosomal alterations. This discovery proved that appetite can be linked to our DNA. Some research suggests a link between the X-chromosome and certain eating disorders. This is because anorexia nervosa and bulimia nervosa are more common in females. Additionally, some forms of obesity are traced to defects in hypothalamic signaling. These defects involve receptors like the leptin receptor or the MC-4 receptor.

Dysregulation of appetite can lead to serious eating disorders. Anorexia nervosa is a mental disorder marked by severe dietary restriction. People with this condition often have an intense fear of weight gain. They may also engage in ritualistic exercise. Interestingly, those with anorexia often have high levels of ghrelin. Their bodies are trying to cause hunger, but the person suppresses the urge to eat. Binge eating disorder, or BED, involves eating uncontrollably during specific intervals. BED is most common in adults, and its heritability is approximately 50%.

Appetite can also be influenced by external and developmental factors. About 25% of children experience "picky eating." This number may be higher in children with developmental disorders. In those cases, sensory processing disorders regarding smells or tastes may be the cause. Stress can also cause appetite levels to increase, leading to more food intake. On the other hand, some diseases cause cachexia, which is a significant loss of appetite and weight. This shows that appetite is not just a feeling, but a complex biological response to many different systems.

Medical science uses various methods to manipulate appetite for treatment. Some drugs are designed to suppress appetite for weight loss. Early examples included fenfluramine and phentermine. Other drugs like sibutramine were withdrawn because they posed cardiovascular risks. Rimonabant was also removed from the market due to links with depression. For those needing to increase appetite, the United States approves three agents. These include megestrol acetate, oxandrolone, and dronabinol. Scientists are also researching ghrelin and the Japanese medicine Rikkunshito to help stimulate appetite.

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